ÇáãÓÍ ÇáÊÕæíÑí Basics of Photogrammetry
ÃÓÇÓíÇÊ ÇáÊÕæíÑí Before describing the operation of the V-STARS system, a brief introduction to photogrammetry is provided for those who are unfamiliar with the technology.
ÞÈá Çä íÕÝ ÊØÈíÞ äÙÇã ÓÊÇÑÒ ÇáÎÇãÓ ¡ ÚÑÖÇ ãæÌÒÇ ááãÓÍ ÇáÊÕæíÑí æÊÞÏã áåÄáÇÁ ÇáÐíä áã íÚÊÇÏæÇ Úáì åÐå ÇáÊßäæáæÌíÇ. Photogrammetry, as its name implies, is a 3-dimensional coordinate measuring technique that uses photographs as the fundamental medium for metrology (or measurement).
æÇáÊÕæíÑ ÇáÌæí ¡ ßãÇ íÏá Úáì Ðáß ÇÓãå ¡ åæ 3 ÊäÓíÞ ÇáÃÈÚÇÏ ÇáÊÞäíÉ ÇáÊí ÊÓÊÎÏã áÞíÇÓ ÇáÕæÑ ÇáÝæÊæÛÑÇÝíÉ ÇáãÊæÓØÉ ÇáÃÓÇÓíÉ áÚáã ÇáÞíÇÓ (Ãæ ÇáÞíÇÓ). The fundamental principle used by photogrammetry is triangulation.
ÇáãÈÏà ÇáÃÓÇÓí ÇáÐí ÊÓÊÎÏãå ÇáãÓÍ ÇáÊÕæíÑí åæ ÇáãËáËÇÊ. By taking photographs from at least two different locations, so-called "lines of sight" can be developed from each camera to points on the object.
ÈÃÎÐ ÕæÑ ãä ÇËäíä Úáì ÇáÃÞá ãä ãæÇÞÚ ãÎÊáÝÉ ¡ ãÇ íÓãì È "ÎØ ÇáÃÝÞ" íãßä æÖÚåÇ ãä ßá äÞØÉ Úáì ÇáßÇãíÑÇ Úáì æÌæå. These lines of sight (sometimes called rays owing to their optical nature) are mathematically intersected to produce the 3-dimensional coordinates of the points of interest.
åÐå ÇáÎØæØ ÇáÈÕÑ (ÇáÊí ÊÓãì ÃÍíÇäÇ ÇáÃÔÚÉ ÇáÖæÆíÉ äÙÑÇ áØÈíÚÉ) ÑíÇÖíÇ ÊÊÏÇÎá áÇäÊÇÌ 3 ÇáÃÈÚÇÏ ÅÍÏÇËíÇÊ äÞÇØ. Triangulation is also the principle used by theodolites for coordinate measurement.
ÇáãËáËÇÊ ÃíÖÇ ãÈÏà ÊÓÊÎÏãå theodolites áÊäÓíÞ ÇáÞíÇÓ. If you are familiar with these instruments, you will find many similarities (and some differences) between photogrammetry and theodolites.
ÅÐÇ ßäÊ ãÚÊÇÏÇ Úáì åÐå ÇáÕßæß ¡ æÓæÝ ÊÌÏ ÇáÚÏíÏ ãä ÃæÌå ÇáÊÔÇÈå) æÈÚÖ ÇáÎáÇÝÇÊ Èíä ÇáãÓÍ ÇáÊÕæíÑí ætheodolites. Even closer to home, triangulation is also the way your two eyes work together to gauge distance (called depth perception).
Èá ÃÞÑÈ Åáì ÇáæØä ¡ æÇáãËáËÇÊ ÃíÖÇ ÇáØÑíÞÉ ÇáÎÇÕÉ Èß Úíäíå ÇáÚãá ãÚÇ áÞíÇÓ ÇáãÓÇÝÉ (íÓãì ÚãÞ ÇáÊÕæÑ).
This primer is separated into two parts.
åÐÇ ÇáÊãåíÏí íäÞÓã Çáì ÌÒÆíä. Photography describes the photographic principles involved in photogrammetry, while Metrology describes the techniques for producing 3-dimensional coordinates from two-dimensional photographs.
ÇáÊÕæíÑ ÇáÝæÊæÛÑÇÝí æíÕÝ ÇáãÈÇÏÆ ÇáÊí íäØæí ÚáíåÇ æÇáÊÕæíÑ ÇáÌæí ¡ Ýí
Ííä Ãä ÇáÞíÇÓ íÕÝ ÊÞäíÇÊ áÅäÊÇÌ 3 ÇáÃÈÚÇÏ ÈÊäÓíÞ ãä ÇáÕæÑ ËäÇÆíÉ ÇáÃÈÚÇÏ.
Photography
ÇáÊÕæíÑ ÇáÝæÊæÛÑÇÝí Photography - The First Part of Photogrammetry
ÇáÊÕæíÑ ÇáÝæÊæÛÑÇÝí -- ÇáÌÒÁ ÇáÃæá ãä ÇáÊÕæíÑí Taking photographs is, of course, essential for making a photogrammetric measurement.
ÇáÊÞÇØ ÇáÕæÑ ¡ ÈØÈíÚÉ ÇáÍÇá
¡ ãä ÇáÖÑæÑí ÅÌÑÇÁ ÇáãÓÍ ÇáÊÕæíÑí ÇáÞíÇÓ. To obtain the high accuracy, reliability and automation the system is capable of, photographs must be of the highest quality.
ááÍÕæá Úáì ÏÑÌÉ ÚÇáíÉ ãä ÇáÏÞÉ æÇáãæËæÞíÉ æÇáÊÔÛíá ÇáÂáí ááäÙÇã ÞÇÏÑ ¡ æíÌÈ Ãä Êßæä ÇáÕæÑ ãä ÃÚáì ãÓÊæíÇÊ ÇáÌæÏÉ. Fortunately, because of the design of the system, photography with V-STARS is actually simpler than film photography.
áÍÓä ÇáÍÙ ¡ æÈÓÈÈ ÊÕãíã åÐÇ ÇáäÙÇã ¡ æÇáÊÕæíÑ ÇáÝæÊæÛÑÇÝí ãÚ ÇáÎÇãÓ ÓÊÇÑÒ Ýí ÇáæÇÞÚ ÃÈÓØ ãä ÊÕæíÑ ÇáÝíáã. The three main considerations for good photography are:
ÇáÑÆíÓíÉ ÇáËáÇËÉ áÇÚÊÈÇÑÇÊ ÍÓä ÇáÊÕæíÑ :
1.
1. Field of View
ãÌÇá ÇáÑÄíÉ Field of View
ãÌÇá ÇáÑÄíÉ The camera's field of view defines how much it sees and is a function of the focal length of the lens and the size (often called the format) of the digital sensor.
ÇáßÇãíÑÇ ãÌÇá ÇáÑÄíÉ æíÚÑÝ ãÏì ãÇ ÊÑÇå åí æÙíÝÉ ãä æÙÇÆÝ ÇáÇÊÕÇá Øæá ÇáÚÏÓÉ æÍÌã (ÛÇáÈÇ ãÇ íØáÞ Úáì ÇáÔßá) ááÇÓÊÔÚÇÑ ÑÞãíÉ. For a given lens, a larger format sensor has a larger field of view.
äÙÑÇ áÚÏÓÉ ¡ ÃßÈÑ ÌåÇÒ ÇáÇÓÊÔÚÇÑ áÞÏ Ôßá ÃæÓÚ ãÌÇá ÇáÑÄíÉ. Similarly, for a given size sensor, a shorter focal length lens has a wider field of view.
æÈÇáãËá ¡ ÈÇáäÓÈÉ áÍÌã ãÚíä ÇáÇÓÊÔÚÇÑ ¡ æÃÞÕÑ ãÏÉ ÊÑßíÒ ÇáÚÏÓÉ æÞÏ ÃæÓÚ ãÌÇá ÇáÑÄíÉ. The relationship between format size, lens focal length and field of view is shown below:
ÇáÚáÇÞÉ Èíä Ôßá æÍÌã ÇáØæá ÇáÈÄÑí ááÚÏÓÉ æãÌÇá ÇáÑÄíÉ ÇáãÈíä ÃÏäÇå :
The standard lenses available with V-STARS are so-called medium angle lenses and have about 50° wide fields of view.
ÇáÚÏÓÇÊ ÇáÞíÇÓíÉ ÇáãÊæÝÑÉ Ýí ÇáÎÇãÓ ÇáäÌæã íÓãì ÒÇæíÉ ÇáÚÏÓÇÊ ÇáãÊæÓØÉ æäÍæ 50 ° ãÌÇáÇÊ æÇÓÚÉ Ýí ÇáÑÃí. The wider the field of view, the more you see from a given location.
Úáì äØÇÞ ÃæÓÚ ãÌÇá ááÑÃí ¡ æÑÃíÊ ÃßËÑ ãä ãæÞÚ ãÚíä. For a medium angle lens, a convenient rule of thumb is that you will generally need to get back as far from the object as the size of the object.
áÒÇæíÉ ÇáÚÏÓÉ ÇáãÊæÓØÉ ¡ æãÑíÍÉ æÈÍßã ÇáÊÌÑÈÉ åí Ãäß ÚãæãÇ ÈÍÇÌÉ Åáì ÇáÚæÏÉ Åáì ÃÞÕì ÍÏ ãä æÌæå ÍíË ÍÌã ÇáÌÓã. For example, you will get about three meters (ten feet) back to see a three-meter (ten foot) object.
Úáì ÓÈíá ÇáãËÇá ¡ ÓÊÍÕá Úáì
ËáÇËÉ ÇãÊÇÑ (ÚÔÑÉ ÃÞÏÇã) ÇäÙÑ Çáì ËáÇËÉ ÇãÊÇÑ (ÚÔÑÉ ÇáÞÏã (æÌæå. In general, there is a tradeoff between the field of view of a lens and accuracy.
ÈÕÝÉ ÚÇãÉ ¡ ËãÉ ãÌÇá ÇáãÞÇíÖÉ Èíä æÌåÇÊ ÇáäÙÑ ãä ãäÙÇÑ æÇáÏÞÉ. Although wider-angle lenses need less room around the object, they also tend to be less accurate.
æÅä ßÇä Úáì äØÇÞ ÃæÓÚ ÇáÒÇæíÉ ÇáÚÏÓÇÊ ÊÍÊÇÌ ÃÞá ÛÑÝÉ Ýí ÌãíÚ ÃäÍÇÁ ÇáÌÓã ¡ ßãÇ ÃäåÇ Êãíá Åáì Ãä Êßæä ÃÞá ÏÞÉ. (The reasons for this are beyond the scope of this introduction.) Thus, you generally want to use the longest focal length lens you can.
(æÃÓÈÇÈ Ðáß íÎÑÌ Úä äØÇÞ åÐÇ ÇáÊÚÑíÝ.) æåßÐÇ ¡ ßäÊ ÊÑÛÈ Ýí ÇÓÊÎÏÇã ÚãæãÇ ÃØæá ãÏÉ ÇáÇÊÕÇá íãßäß ÇáÚÏÓÉ. The medium angle lenses provided with V-STARS represent a good compromise between field of view and accuracy.
ÒÇæíÉ ÇáãÊæÓØ ÇáÚÏÓÇÊ ÊÒæíÏ ÇáÎÇãÓ ÓÊÇÑÒ ÊãËá ÍáÇ æÓØÇ ÌíÏÇ Èíä ãÌÇá ÇáÑÄíÉ æÇáÏÞÉ. Focusing
ÇáÊÑßíÒ One consideration for normal photography is, of course, focusing the lens so the image is sharp.
æÇÍÏÉ ááäÙÑ Ýí ÇáÊÕæíÑ ÇáÚÇÏí ¡ ÈØÈíÚÉ ÇáÍÇá
¡ ÈÍíË ÊÑßÒ ÇáÚÏÓÉ ÇáÕæÑÉ ÊãÇãÇ. The range of acceptable sharpness is called the depth of focus.
ãÌãæÚÉ ãÞÈæáÉ ãä ÍÏÉ ÊÓãì ÚãÞ ÇáÊÑßíÒ. The depth of focus of a lens is a function of many factors, including: the focal length of the lens, the format size, the distance from the camera to the object, the size of the object, and the f-number of the lens.
ÚãÞ ÈÄÑÉ ÚÏÓÉ ÊÊæÞÝ Úáì ÚæÇãá ßËíÑÉ ¡ ãäåÇ : ÇáÇÊÕÇá Øæá ÇáÚÏÓÉ ¡ æÔßá æÍÌã ÇáãÓÇÝÉ ãä ÇáßÇãíÑÇ Åáì æÌæå ¡ æÍÌã ÇáÌÓã ¡ ææ Èíä
ÚÏÏ ãä ÇáÚÏÓÇÊ . As you can appreciate from all the factors listed above, the depth of focus can be a complex function.
ßãÇ íãßäß Ãä äÞÏÑ ãä ßá ÇáÚæÇãá ÇáãÐßæÑÉ ÃÚáÇå ¡ Úáì ÚãÞ ÇáÊÑßíÒ æíãßä Ãä íßæä ãåãÉ ãÚÞÏÉ. V-STARS has been designed so that images will be in acceptable focus for points between 0.5 meters (20 inches) and 60 meters (200 feet) from the camera.
ÇáÎÇãÓ ÓÊÇÑÒ æÞÏ Õãã ÈÍíË íßæä Ýí ÕæÑÉ ãÞÈæáÉ ááäÞÇØ ÇáÊÑßíÒ Èíä 0.5 ãÊÑ (20 ÈæÕÉ) æ 60 ãÊÑÇ (200 ÞÏãÇ) ãä ÇáßÇãíÑÇ. Fixing the focus effectively eliminates the depth of focus problem.
ÊÍÏíÏ ÇáÊÑßíÒ ÈÔßá ÝÚÇá íÞÖí Úáì ÇáÊÑßíÒ Úáì ÚãÞ ÇáãÔßáÉ.
Exposure
ÇáÊÚÑÖ Camera Exposure
ÊÚÑÖ ÇáßÇãíÑÇ For photogrammetry purposes, it is desirable to set the targets bright and the background dim.
áÃÛÑÇÖ ÇáãÓÍ ÇáÊÕæíÑí ¡ ãä
ÇáãÓÊÍÓä Ãä ÊÍÏÏ ÇáÃåÏÇÝ æãÔÑÞ ÎáÝíÉ ÞÇÊãÉ. When retro-reflective targeting is used, the target and background exposures are almost completely independent of each other.
ÚäÏãÇ ÚÇßÓÉ ÊÓÊåÏÝ ÇÓÊÎÏÇã ÇáåÏÝ æÇáÎáÝíÉ ÇáÊÚÑÖ ÔÈå ãÓÊÞáÉ ÊãÇãÇ Úä ÈÚÖåÇ ÇáÈÚÖ. The target exposure is completely determined by the flash power while the background exposure is determined by the ambient illumination. The amount of background exposure is controlled by the shutter time.
ÇáåÏÝ åæ ÇáÊÚÑÖ ÊÍÏÏåÇ ÇáÓáØÉ ÝáÇÔ Ííä ÇáÊÚÑÖ ááãÕãã ÇáÅÖÇÁÉ ÇáãÍíØÉ ÈåÇ. ãÞÏÇÑ ÇáÊÚÑÖ ÊÓíØÑ ÚáíåÇ ãÕÑÇÚ ÇáæÞÊ.
Eliminating the background exposure makes the targets easier to find and measure.
ÇáÞÖÇÁ Úáì ÎáÝíÉ ÇáÊÚÑÖ íÌÚá ãä ÇáÃÓåá ÇáÚËæÑ Úáì ÃåÏÇÝ æÇáÊÏÈíÑ. However, if there is no background image whatsoever, trying to figure out which target is which can be difficult.
æãÚ Ðáß ¡ ÅÐÇ áã Êßä åäÇß ÕæÑÉ ÎáÝíÉ Úáì ÇáÇØáÇÞ ¡ Ýí ãÍÇæáÉ áãÚÑÝÉ ÇáåÏÝ ÇáÐí íãßä Ãä íßæä ÕÚÈÇ. Usually, a compromise is reached and the background exposure is set so the object is dim enough to not interfere with target measurement, but still bright enough that it can be seen when enhanced.
ÚÇÏÉ ¡ íÊã ÇáÊæÕá Åáì Íá æÓØ æÎáÝíÉ Ðáß æãä ÇáãÞÑÑ Çä ÊÚÑÖ ÇáÌÓã ÞÇÊãÉ ÈãÇ íßÝí áÚÏã ÇáÊÏÎá Ýí ÞíÇÓ ÇáåÏÝ ¡ áßäåÇ ãÇ ÒÇáÊ ãÔÑÞÉ íßÝí Ãäå íãßä ãáÇÍÙÉ ÚäÏãÇ ÊÚÒíÒåÇ. Background Exposure
ÎáÝíÉ ÇáÊÚÑÖ The shutter time is used to control the background exposure.
ÝÅä ÇáæÞÊ ãÕÑÇÚ ÊÓÊÎÏã ááÓíØÑÉ Úáì ÎáÝíÉ ÇáÊÚÑÖ. When the camera is off-line, the shutter time is selected using the mode switches that are located on the top of the camera next to the display.
ÚäÏãÇ Êßæä ÇáßÇãíÑÇ ÎÇÑÌ ÇáÔÈßÉ ¡ æãÕÑÇÚ ÇáßÇãíÑÇ ÇáÊí ÊÓÊÎÏã ãÑÉ æíÊã ÇÎÊíÇÑ ØÑíÞÉ ÇáãÝÇÊíÍ ÇáÊí ÊÞÚ Úáì ÑÃÓ ÇáßÇãíÑÇ Çáì ÇáÔÇÔÉ. The available shutter times on an INCA2 range from 8 milliseconds to 8 seconds.
ãÕÑÇÚ ÇáãÊÇÍÉ INCA2 ãÑÇÊ Úáì ãÏì ÇáÝÊÑÉ ãä 8 Åáì 8 ãáí ËÇäíÉ.
The INCA2 camera has an AUTO Exposure feature that can be used to automatically set the shutter speed.
ÝÅä ÇáßÇãíÑÇ INCA2 ÇáÊÚÑÖ áåÇ ÓãÉ ÇáÓíÇÑÇÊ ÇáÊí íãßä ÇÓÊÎÏÇãåÇ áÊáÞÇÆíÇ ÍÏÏ ÓÑÚÉ ãÕÑÇÚ ÇáßÇãíÑÇ. The default setting is to use the AUTO Exposure.
ÇáÅÚÏÇÏ ÇáÇÝÊÑÇÖí åæ ÇÓÊÎÏÇã ÇáÓíÇÑÇÊ ÇáÊÚÑÖ. If AUTO Exposure is selected, the shutter exposure is set automatically the first time you take a picture on a job.
ÅÐÇ ßÇä ÇáÊÚÑÖ ááÓíÇÑÇÊ ÇÎÊíÇÑ ¡ æãä ÇáãÞÑÑ Ãä ÊÚÑÖ ãÕÑÇÚ ÊáÞÇÆíÇ Ãæá ãÑÉ ÊÊÎÐ ÕæÑÉ Úä æÙíÝÉ. Target Exposure
ÇáåÏÝ ÇáÊÚÑÖ The flash power setting for the target exposure depends on the distance from the camera to the targets, and the target size.
ÇáÚÇÌá áæÖÚ ÇáÓáØÉ åÏÝÇ ÇáÊÚÑÖ íÊæÞÝ Úáì ãÓÇÝÉ æÇÍÏÉ ãä ÇáßÇãíÑÇ Çáì ÇåÏÇÝ ¡ æÍÌã ÇáåÏÝ.
The following diagram gives recommended flash power settings at varying distances.
æÝíãÇ íáí ÑÓã ÈíÇäí íÚØí ÝáÇÔ ÃæÕÊ ÓáØÉ ÇáÖÈØ Úáì ãÓÇÝÇÊ ãÊÝÇæÊÉ. If you are shooting the object in sections, use the size of the sections.
ÅÐÇ ßäÊ åÏÝÇ áÇØáÇÞ ÇáäÇÑ Ýí ÇáÝÑæÚ ¡ æÇÓÊÎÏÇã ÍÌã ÇáÝÑæÚ. The tables assume the recommended target size (which is also listed) is used.
ÇáÌÏÇæá ÊÍãá ÃæÕÊ ÍÌã ÇáåÏÝ (ÇáÐí åæ ÇíÖÇ) íÓÊÎÏã. If the targets are smaller than this, you may want to increase the flash power setting one step to help compensate.
ÅÐÇ ßÇäÊ ÇáÃåÏÇÝ åí ÃÕÛÑ ãä Ðáß ¡ ÞÏ ÊÑÛÈ Ýí ÒíÇÏÉ ÇáØÇÞÉ æÖÚ ÇáÝáÇÔ ÎØæÉ æÇÍÏÉ ááãÓÇÚÏÉ Ýí ÊÚæíÖ åÐÇ ÇáäÞÕ. The tables assume the default lens f-number of F11 is used with an INCA.
ÌÏÇæá ÊÍãá ÇáÇÝÊÑÇÖí ÚÏÓÉ æ Èíä
ÚÏÏ ãä F11 íÓÊÎÏã ãÚ ÇáÅäßÇ. It is important to check the lens and make sure it is set to f11, the default setting for the lens.
æãä Çáãåã ÇáÊÃßÏ ãä ÇáÚÏÓÇÊ æÇáÊÃßÏ ãä Ãäå ãä ÇáãÞÑÑ Ãä F11 ¡ ÇáÅÚÏÇÏ ÇáÇÝÊÑÇÖí ááÚÏÓÉ. Metrology
ÇáÞíÇÓ Metrology - The Second Part of Photogrammetry
ÇáÞíÇÓ -- ÇáÌÒÁ ÇáËÇäí ãä ÇáÊÕæíÑí Photography in its broadest sense is a process that converts the real 3-dimensional world into flat 2-dimensional images. The camera is the device that makes this transformation or mapping from 3 dimensions to 2 dimensions.
ÇáÊÕæíÑ ÇáÝæÊæÛÑÇÝí Ýí ÃæÓÚ ãÚÇäíåÇ åí ÚãáíÉ ÊÍæíá ÇáÍÞíÞí 3 ÇáÃÈÚÇÏ ÇáÚÇáã Ýí ÔÞÉ 2 ÕæÑ ãÌÓãÉ. ÇáßÇãíÑÇ ÇáÌåÇÒ ÇáÐí íÌÚá åÐÇ ÇáÊÍæá ¡
Ãæ ÑÓã ÇáÎÑÇÆØ Ýí ÇáÝÊÑÉ ãä 3 Åáì 2 ÇáÃÈÚÇÏ ÇáÃÈÚÇÏ. Unfortunately, we cannot map the 3-dimensional world onto two dimensions completely so some information is lost (primarily the depth).
áÓæÁ ÇáÍÙ ¡ áÇ íãßääÇ ÑÓã ÎÑíØÉ ÇáÚÇáã (3) ÇáÃÈÚÇÏ Úáì ÈÚÏíä ÊãÇãÇ ÍÊì ÈÚÖ ÇáãÚáæãÇÊ ÇáãÝÞæÏÉ (Ýí ÇáãÞÇã ÇáÃæá Úáì ÚãÞ).
Photogrammetry in its broadest sense reverses the photographic process described above.
ÇáãÓÍ ÇáÊÕæíÑí Ýí ÃæÓÚ ãÚÇäíåÇ íÚßÓ ÇáÝæÊæÛÑÇÝíÉ ÇáÚãáíÉ ÇáãæÕæÝÉ ÃÚáÇå. It converts or maps the flat 2-dimensional images back into the real 3-dimensional world.
æåæ íÍæá ÎÑÇÆØ Ãæ ÇáÔÞÉ ÕæÑ ãÌÓãÉ 2 Çáì 3 ÇáÃÈÚÇÏ ÇáÍÞíÞíÉ ÇáÚÇáã. However, since information is lost in the photographic process, we cannot reconstruct the 3-dimensional world completely with just one photograph.
æáßä ÈãÇ Ãä ÇáãÚáæãÇÊ ÇáãÝÞæÏÉ Ýí ÚãáíÉ ÇáÊÕæíÑ ¡ áÇ íãßä ÅÚÇÏÉ ÈäÇÁ ÇáÚÇáã 3 ÇáÃÈÚÇÏ ÊãÇãÇ ãÚ ÕæÑÉ æÇÍÏÉ ÝÞØ. As a minimum, we require two different photographs to reconstruct the 3-dimensional world.
ßÍÏ ÃÏäì ¡ äØáÈ
ÕæÑ ãÎÊáÝÉ áÅÚÇÏÉ ÈäÇÁ 3 ÇáÃÈÚÇÏ ÇáÚÇáã. If this process was perfect, the two photographs are more than enough information to perfectly reconstruct the 3-dimensional world they represent.
ÅÐÇ ÃÑíÏ áåÐå ÇáÚãáíÉ åæ ãËÇáí ¡ æåãÇ ÃßËÑ ãä ÇáÕæÑ ãÚáæãÇÊ ßÇÝíÉ ÊãÇãÇ áÅÚÇÏÉ ÈäÇÁ ÇáÚÇáã 3 ÇáÃÈÚÇÏ ÇáÊí ÊãËáåÇ. Unfortunately, the photography and measuring process is not perfect so the reconstruction of the 3-dimensional world is also imperfect.
æããÇ íÄÓÝ áå
¡ æÇáÊÕæíÑ ÇáÝæÊæÛÑÇÝí æÞíÇÓ ÚãáíÉ áíÓÊ ßÇãáÉ ÍÊì ÅÚÇÏÉ ÈäÇÁ 3 ÇáÃÈÚÇÏ ÇáÚÇáã ÃíÖÇ ÇáßãÇá. However, we can take more photographs and use the extra information in them to improve the process.
æãÚ Ðáß ¡ ÝÅääÇ íãßä Ãä ÊÊÎÐ ÇáãÒíÏ ãä ÇáÕæÑ æÇáãÚáæãÇÊ ÇáÇÖÇÝíÉ ÇáÊí ÊÓÊÎÏã ÝíåÇ áÊÍÓíä åÐå ÇáÚãáíÉ. The 3-dimensional coordinates we produce from the measurements of multiple photographs are the end result of photogrammetry.
3 ÇáÃÈÚÇÏ ÇáÅÍÏÇËíÇÊ ÇáÊí ääÊÌåÇ ãä ÞíÇÓÇÊ ãÊÚÏÏÉ ÇáÕæÑ ÇáÝæÊæÛÑÇÝíÉ åí ÇáäÊíÌÉ ÇáäåÇÆíÉ ááãÓÍ ÇáÊÕæíÑí. Photogrammetry uses the basic principle of Triangulation, whereby intersecting lines in space are used to compute the location of a point in all three dimensions.
æÇáÊÕæíÑ ÇáÌæí æíÓÊÎÏã ÇáãÈÏà ÇáÃÓÇÓí ááÊæÌíå ¡ ÍíË ÇáÎØæØ ÇáãÊÏÇÎáÉ Ýí ÇáÝÖÇÁ ÇáãÓÊÎÏãÉ áãæÞÚ äÞØÉ Ýí ÌãíÚ ÇáÃÈÚÇÏ ÇáËáÇËÉ. However, in order to triangulate a set of points one must also know the camera position and aiming angles (together called the orientation) for all the pictures in the set.
æãÚ Ðáß ¡ ãä
ÃÌá ãÌãæÚÉ ãä ËáË äÞØÉ æÇÍÏÉ íÌÈ ÇíÖÇ Çä äÚÑÝ ãæÞÝ ÇáßÇãíÑÇ æÇáÒæÇíÇ ÇáÊí ÊåÏÝ (Åáì ÌÇäÈ æÕÝ ÇáÊæÌå áÌãíÚ ÇáÕæÑ Ýí ÇáãÌãæÚÉ. A process called Resection does this.
ÚãáíÉ ÇáÇÓÊÆÕÇá ÇáÌÒÆí áÇ íÓãì Ðáß. Finally, because the V-STARS camera is a precision measuring instrument, it must be calibrated so its errors can be defined and removed.
æÃÎíÑÇ ¡ áÃä ãä ÇáÎÇãÓ ÓÊÇÑÒ ÇáßÇãíÑÇ åí ÃÏÇÉ áÞíÇÓ ÇáÏÞÉ ¡ áÇ
ÈÏ ãä ÃÎØÇÆå ãÍÓæÈÉ ÈÍíË íãßä ÊÚÑíÝåÇ æÅÒÇáÊåÇ. One of the most powerful features of V-STARS is its ability to produce this camera calibration as a byproduct of the measurement in a process called Self-calibration.
æÇÍÏÉ ãä ÃÞæì ÇáÓãÇÊ ÇáÎÇãÓ ÓÊÇÑÒ åí ÞÏÑÊåÇ Úáì ÅäÊÇÌ åÐå ÇáßÇãíÑÇ ÇáãÚÇíÑÉ ÈÇÚÊÈÇÑåÇ äÊíÌÉ ËÇäæíÉ ááÞíÇÓ Ýí ÚãáíÉ ÊÓãì ÇáÐÇÊí ÇáãÚÇíÑÉ. Although each of these techniques is best described separately, they are actually all performed simultaneously in a process called the Bundle Adjustment.
Úáì ÇáÑÛã ãä ßá åÐå ÇáÊÞäíÇÊ åæ ÃÝÖá æÕÝ Úáì ÍÏÉ ¡ Ýåí
Ýí ÇáæÇÞÚ ÇáÞíÇã Ýí æÞÊ æÇÍÏ Ýí ßá ÚãáíÉ ÊÓãì ÇáÊßíÝ ÇáÍÒãÉ.
Triangulation
ÇáãËáËÇÊ Triangulation is the principle used by both photogrammetry and theodolites to produce 3-dimensional point measurements.
ÇáãËáËÇÊ åæ ãÈÏà íÓÊÎÏãåÇ ßá ãä ÇáãÓÍ ÇáÊÕæíÑí ætheodolites áÇäÊÇÌ 3 äÞØÉ ÞíÇÓ ÇáÃÈÚÇÏ. By mathematically intersecting converging lines in space, the precise location of the point can be determined.
ÑíÇÖíÇ Èå ÊÊáÇÞì ÇáÎØæØ ÇáãÊÏÇÎáÉ Ýí ÇáÝÖÇÁ ¡ æÊÍÏíÏ ÇáãæÞÚ ÇáÏÞíÞ ááíãßä ÊÍÏíÏ äÞØÉ. However, unlike theodolites, photogrammetry can measure multiple points at a time with virtually no limit on the number of simultaneously triangulated points.
æáßä ¡ ÎáÇÝÇ theodolites ¡ æÇáÊÕæíÑ æíãßä ÞíÇÓ ÚÏÉ äÞÇØ Ýí ÇáæÞÊ ÇáÐí íßÇÏ íÎáæ ãä Ãí ÊÍÏíÏ áÚÏÏ ãä ÇáäÞÇØ Ýí æÞÊ æÇÍÏ ãËáË.
In the case of theodolites, two angles are measured to generate a line from each theodolite.
Ýí ÍÇáÉ theodolites ÇËäíä ÞíÇÓ ÇáÒæÇíÇ áÊæáíÏ ÎØ ãä ßá ÇáãÒæÇÉ ÌåÇÒ ÞíÇÓ ÇáÒæÇíÇ. In the case of photogrammetry, it is the two-dimensional (x, y) location of the target on the image that is measured to produce this line.
Ýí ÍÇáÉ ÇáãÓÍ ÇáÊÕæíÑí ¡ Èá
åí ËäÇÆíÉ ÇáÃÈÚÇÏ (Î ¡ Ð) ãæÞÚ ÇáãÓÊåÏÝ Úáì ÇáÕæÑÉ ÇáÊí ÊÞÇÓ Úáì ÅäÊÇÌ åÐÇ ÇáÎØ. By taking pictures from at least two different locations and measuring the same target in each picture a "line of sight" is developed from each camera location to the target.
ÇáÊÞÇØ ÇáÕæÑ ãä ÞÈá ÇËäíä Úáì ÇáÃÞá ãä ãæÇÞÚ ãÎÊáÝÉ æÞíÇÓ ÇáåÏÝ äÝÓå Ýí ßá ÕæÑÉ "ÎØ ÇáÑÄíÉ" æÖÚÊ ÇáßÇãíÑÇ ãä ßá ãßÇä áåÐÇ ÇáåÏÝ. If the camera location and aiming direction are known (we describe how this is done in Resection), the lines can be mathematically intersected to produce the XYZ coordinates of each targeted point.
ÅÐÇ ßÇäÊ ßÇãíÑÇ ãæÞÚ æíåÏÝ ÇáÇÊÌÇå ÇáãÚÑæÝ (æÕÝ ßíÝ íÊã Ðáß Ýí ÇáÇÓÊÆÕÇá ÇáÌÒÆí) ¡ æÝÞÇ áãÇ íãßä Ãä íßæä ÑíÇÖíÇ ÊÊÏÇÎá áÇäÊÇÌ XYZ íäÓÞ ßá ÇÓÊåÏÝÊ äÞØÉ. Resection
ÈÊÑ Resection is the procedure used to determine the final position and aiming (called the orientation) of the camera when a picture is taken. Typically all the points that are seen and known in XYZ in the image are used to determine this orientation.
ÈÊÑ åí ÇáÅÌÑÇÁÇÊ ÇáãÓÊÎÏãÉ áÊÍÏíÏ ÇáæÖÚ ÇáäåÇÆí æÇáÊí ÊåÏÝ (íÓãì ÇáÊæÌå) ãä ÇáßÇãíÑÇ ÚäÏãÇ ÃÎÐ ÕæÑÉ. ÚÇÏÉ ÌãíÚ ÇáäÞÇØ ÇáÊí ÊÚÊÈÑ æãÚÑæÝ Ýí XYZ Ýí ÕæÑÉ ÊÓÊÎÏã áÊÍÏíÏ ãÇ ÇÐÇ ßÇä åÐÇ ÇáÊæÌå. V-STARS uses the AutoStart or SuperStart operation to get the preliminary camera orientation. This orientation is based on the AutoBar or any known coded targets.
ÇáÎÇãÓ ÓÊÇÑÒ íÓÊÎÏã ÊÔÛíá ÊáÞÇÆí Ãæ SuperStart ÇáÊÔÛíá ÇáÃæáíÉ ááÍÕæá Úáì ÇáßÇãíÑÇ ÇáÊæÌå æåÐÇ ÇáÊæÌå íÓÊäÏ AutoBar Ãæ ÑãæÒÇ ãÚÑæÝÉ ÇáÃåÏÇÝ. For a strong resection, you should have at least twelve well-distributed points in each photograph. If your measurement does not have this many points, or they are not well distributed, it is recommendable to add points.
áÈÊÑ ÞæíÉ ¡ íÌÈ Ãä áÇ íÞá Úä ÇËäí ÚÔÑ äÞÇØ ãæÒÚÉ ÈÔßá ÌíÏ Ýí ßá ÕæÑÉ. ÇáÞíÇÓ ÅÐÇ ßÇä áÇ íãáß ÇáßËíÑ ãä åÐå ÇáäÞÇØ ¡ Ãæ ÃäåÇ áíÓÊ ãæÒÚÉ ÈÔßá ÌíÏ ¡ æãä ÇáãÝÖá Ãä ÃÖíÝ äÞØÉ. Points that are added to strengthen the solution are called "fill-in" points.
ãä ÇáäÞÇØ ÇáÊí ÃÖíÝÊ áÊÚÒíÒ ÇáÍá íØáÞ Úáíåã ÇÓã "ÇáÔåÇÏÉ". If the XYZ coordinates of the points on the object are known (we describe in Triangulation how this is done), we can compute the camera's orientation.
ÅÐÇ XYZ ÅÍÏÇËíÇÊ ÇáäÞÇØ Úáì æÌæå ãÚÑæÝÉ (Ýí ÊæÌíå æÕÝ ßíÝ íÊã Ðáß) ¡ æíãßääÇ Ãä ÊÍÓÈ ÇáßÇãíÑÇ ÇáÊæÌå. It is important to realize that both the position and aiming direction of the camera are needed.
æãä Çáãåã Ãä äÏÑß Ãä ßáÇ ãä ãäÕÈ æÊåÏÝ ÇÊÌÇå ÇáßÇãíÑÇ ÇáãØáæÈÉ. It is not sufficient to know only the camera's position since the camera could be located in the same place but be aimed in any direction.
ÇäåÇ áíÓÊ ßÇÝíÉ æÍÏåÇ áãÚÑÝÉ ãæÞÝ ÇáßÇãíÑÇ áÃä ÇáßÇãíÑÇ íãßä Ãä ÊÞÚ Ýí äÝÓ ÇáãßÇä æáßä ãä ÃÌá Ãä íßæä Ýí Ãí ÇÊÌÇå. Consequently, we must know the camera's position which is defined by three coordinates, and where it is aimed which is defined by three angles.
æÈÇáÊÇáí ¡ íÌÈ ÚáíäÇ Ãä äÚÑÝ ãæÞÝ ÇáßÇãíÑÇ ÇáÊí ÊÍÏÏåÇ ËáÇËÉ ÅÍÏÇËíÇÊ ¡ æÍíËãÇ ßÇä Ðáß åæ ÇáåÏÝ ÇáÐí ÍÏÏÊå ËáÇË ÒæÇíÇ. Thus, although three values are needed to define a target point (three coordinates for its position), we need six values to define a picture (three coordinates for
æåßÐÇ ¡ Úáì
ÇáÑÛã ãä ÇáÞíã ÇáËáÇË åäÇß ÍÇÌÉ áÊÍÏíÏ åÏÝ äÞØÉ (ËáÇËÉ ÊäÓÞ ãæÞÝåÇ) ¡ ÝÅääÇ ÈÍÇÌÉ Åáì ÊÍÏíÏ ÇáÞíã ÓÊÉ ÕæÑÉ) ËáÇËÉ ÅÍÏÇËíÇÊ position, and three angles for the aiming direction).
ÇáãæÞÝ ¡ æËáÇË ÒæÇíÇ ááÈåÏÝ ÇáÇÊÌÇå). Self-Calibration
ãÚÇíÑÉ ÇáÐÇÊí Although the cameras and lenses used in the V-STARS system are of the highest quality, they must still be precisely calibrated to remove errors that are present in the system.
æÑÛã Ãä ÚÏÓÇÊ ÇáßÇãíÑÇÊ ÇáãÓÊÎÏãÉ Ýí ÇáÎÇãÓ ãä äÙÇã ÓÊÇÑÒ ÃÚáì ãÓÊæì ãä ÇáÌæÏÉ ¡ íÌÈ Ãä Êßæä ãÍÓæÈÉ ÈÏÞÉ áÅÒÇáÉ ÇáÃÎØÇÁ ÇáãæÌæÏÉ Ýí ÇáäÙÇã. Some of these error terms can be described in terms of their physical cause while others are more empirically derived.
ÈÚÖ åÐå ÇáÃÎØÇÁ ÍíË íãßä æÕÝåÇ ãä ÍíË äÊÇÆÌåÇ ÇáãÇÏíÉ ÓÈÈÇ Ýí Ííä Ãä ÇáÈÚÖ ÇáÂÎÑ ÃßËÑ ÊÌÑíÈíÉ ÇáãÔÊÞÉ. In any case, all of these error terms are automatically solved for by V-STARS along with the XYZ coordinates of the target points and the orientation (position and aiming angles) of each picture in a process called the Bundle Adjustment.
Úáì ÃíÉ ÍÇá ¡ ßá åÐå ÇáÃÎØÇÁ ãä ÍíË ÊÍá ÊáÞÇÆíÇ ãä ÎáÇá áÇáÎÇãÓ ÓÊÇÑÒ ãÚ XYZ ÅÍÏÇËíÇÊ ÇáåÏÝ æÇáÊæÌå äÞØÉ) æíåÏÝ ãæÞÚ ÒæÇíÇ) áßá ÕæÑÉ Ýí ÚãáíÉ ÊÓãì ÇáÊßíÝ ÇáÍÒãÉ. This ability to calibrate the camera as a byproduct of the measurement is called Self-calibration and it means the camera will be calibrated at the time of measurement, and under the environmental conditions that exist (temperature, humidity, etc.) at the time of measurement.
åÐå ÇáÞÏÑÉ Úáì ãÚÇíÑÉ ÇáßÇãíÑÇ ÈÇÚÊÈÇÑåÇ ãäÊÌÇ ËÇäæíÇ ááÞíÇÓ æÇáãÚÇíÑÉ æÏÚÇ ÇáÐÇÊí.. æåæ ãÇ íÚäí ÇáßÇãíÑÇ ÓÊßæä ãÍÓæÈÉ Ýí æÞÊ ÇáÞíÇÓ ¡ æÊÍÊ ÇáÙÑæÝ ÇáÈíÆíÉ ÇáÞÇÆãÉ (ÇáÍÑÇÑÉ æÇáÑØæÈÉ ¡ æÛíÑ Ðáß) Ýí æÞÊ ÇáÞíÇÓ. This is far superior to relying on an old and possibly outdated laboratory calibration that may have been done under dramatically different conditions than existed at the time of measurement.
æåÐÇ ÃÚáì ÈßËíÑ ÇáÇÚÊãÇÏ Úáì ÇáÞÏíã ¡
æÑÈãÇ ÝÇÊ ÃæÇäåÇ ãÎÊÈÑ ÇáãÚÇíÑÉ ÇáÊí íãßä Ãä íÊã Ðáß Ýí Ùá ÙÑæÝ ãÎÊáÝÉ ÈÔßá ßÈíÑ ÚãÇ ßÇäÊ ãæÌæÏÉ æÞÊ ÇáÞíÇÓ. There are certain requirements that must be met in order to self-calibrate a camera, but they are usually easy to do.
åäÇß ÈÚÖ ÇáãÊØáÈÇÊ ÇáÊí íÌÈ ÇáæÝÇÁ ÈåÇ ãä ÃÌá ÊÞÑíÑ ÇáãÕíÑ ¡
ãÚÇíÑÉ ÇáßÇãíÑÇ ¡ áßäåÇ Êßæä ÚÇÏÉ ãä ÇáÓåá ÇáÞíÇã Èå. First, the measurement must have what is called roll diversity. This usually means you must take some photographs with the camera horizontal and some photographs with the camera vertical.
ÃæáÇ ¡ íÌÈ Ãä íßæä ÞíÇÓ ãÇ íÓãì ÞÇÆãÉ Úáì ÇáÊäæÚ æåÐÇ íÚäí ÚÇÏÉ ¡
íÌÈ Çä ÊÃÎÐ ÈÚÖ ÇáÕæÑ ãÚ ÇáßÇãíÑÇ ÇáÃÝÞíÉ æÈÚÖ ÇáÕæÑ ÇáÝæÊæÛÑÇÝíÉ ãÚ ÇáßÇãíÑÇ ÇáÑÃÓí. Although you will get better results if you take about half of your shots one-way and half the other, this is not critical.
æÑÛã Ãä ÊÍÕá Úáì äÊÇÆÌ ÃÝÖá ÅÐÇ ßäÊ ÊÃÎÐ ãÇ íÞÑÈ ãä äÕÝ ÇáØáÞÇÊ ÇáÎÇÕÉ Èß Ýí ÇÊÌÇå æÇÍÏ ¡
æÇáäÕÝ ÇáÂÎÑ ¡ æåÐå áíÓÊ ÍÑÌÉ. What is critical is that you must have at least one picture that is rolled approximately 90° differently than the others.
ãÇ åæ ÈÇáÛ ÇáÃåãíÉ åæ Ãäå íÌÈ Ãä íßæä áÏíß ÕæÑÉ æÇÍÏÉ Úáì ÇáÃÞá åÐÇ åæ ãÇ íÞÑÈ ãä 90 ÏÑÌÉ ÇáãÏáÝä ãÎÊáÝ Úä ÇáÂÎÑíä. If you do not, you cannot self-calibrate the camera.
ÅÐÇ ßäÊ áÇ ¡ áÇ íãßäß ÇáÐÇÊí ãÚÇíÑÉ ÇáßÇãíÑÇ. Instead, you will have to rely on a pre-existing calibration that is less reliable and less accurate.
æÈÏáÇ ãä Ðáß ¡ åá Óíßæä ÇáÇÚÊãÇÏ Úáì ÇáÞÇÆãÉ ãä ÞÈá ÇáãÚÇíÑÉ åí ÃÞá ãæËæÞíÉ æÃÞá ÏÞÉ. A second requirement is that you must measure a minimum number of photographs taken from a minimum number of different locations.
æÇáãØáÈ ÇáËÇäí åæ Ãäå íÌÈ Úáíß ÞíÇÓ ÚÏÏ ÃÏäì ãä ÇáÕæÑ ÇáÝæÊæÛÑÇÝíÉ ÇáÊí ÇáÊÞØÊ ãä ÇáÍÏ ÇáÃÏäì áÚÏÏ ãä ãæÇÞÚ ãÎÊáÝÉ. You should measure at least six photographs if the object is two-dimensional (the object is essentially flat) or four photographs if the object is three-dimensional.
íÌÈ Úáíß ÞíÇÓ áÇ íÞá Úä ÓÊÉ ÕæÑ ÝæÊæÛÑÇÝíÉ ÅÐÇ ßÇä ÇáÌÓã ËäÇÆíÉ ÇáÃÈÚÇÏ (ãæÖæÚ ÃÓÇÓÇ ÔÞÉ) Ãæ ÃÑÈÚ ÕæÑ ÝæÊæÛÑÇÝíÉ ÅÐÇ ßÇä ÇáÌÓã ËáÇËíÉ ÇáÃÈÚÇÏ. Also, the photographs should be taken from at least three different locations.
ßÐáß ¡ íäÈÛí Ãä Êßæä ÇáÕæÑ ãÃÎæÐÉ ãä ËáÇËÉ Úáì ÇáÃÞá ãä ãæÇÞÚ ãÎÊáÝÉ. Since most jobs will take at least this many photographs there is usually no reason not to self-calibrate the camera.
æÈãÇ Ãä ãÚÙã ÇáæÙÇÆÝ ÓíÓÊÛÑÞ Úáì ÇáÇÞá åÐÇ åäÇß ÇáÚÏíÏ ãä ÇáÕæÑ ÚÇÏÉ Ãí ÓÈÈ áÚÏã ÇáÐÇÊí ãÚÇíÑÉ ÇáßÇãíÑÇ. In fact, we strongly recommend that you always take enough photographs to self-calibrate the camera because it is so quick and easy to take and measure extra photographs.
Ýí æÇÞÚ ÇáÃãÑ
¡ ÝÅääÇ äæÕí ÈÞæÉ ÈÃä ÊÊÎÐ áß ÏÇÆãÇ ãÇ íßÝí ãä ÕæÑ ÇáÐÇÊ ãÚÇíÑÉ ÇáßÇãíÑÇ áÃäå ÓÑíÚ æÓåá Ðáß áÇÊÎÇÐ ÇáÇÌÑÇÁ ÇáÇÖÇÝí æÕæÑ ÝæÊæÛÑÇÝíÉ. A final requirement is that you must have a minimum number of well-distributed points on each photograph and for the entire measurement.
äåÇÆí íÊãËá ÇáãØáÈ íÌÈ Ãä íßæä áÏíß ÃÏäì ÚÏÏ ãä ÇáäÞÇØ ÇáÊí æÒÚÊ ÈÔßá ÌíÏ Ýí ßá ÕæÑÉ ¡
æáßá ÞíÇÓ. Specifically, you should have at least twelve well-distributed points on each photograph, and at least twenty points for the entire measurement.
æÊÍÏíÏÇ ¡ íÌÈ Úáì ÇáÃÞá ÇËäí ÚÔÑ äÞÇØ ÌíÏÉ æÒÚÊ Úáì ßá ÕæÑÉ ¡ æíÞá Úä ÚÔÑíä äÞØÉ áßá ÞíÇÓ. Well-distributed means the points are distributed fairly evenly throughout the photograph.
æÓíáÉ ÌíÏÉ æÒÚÊ ÇáäÞÇØ ãæÒÚÉ ÈÇáÊÓÇæí Ýí ÌãíÚ ÃäÍÇÁ ÇáÕæÑÉ. It is much better for example to have twelve points distributed evenly throughout the picture than to have fifty clustered together in one small area. If you do not happen to need this many points for the measurement or they are not well distributed, we recommend you add points to the measurement. As you will see, it is very quick and easy to add extra points to the measurement so feel free to do so.
æãä ÃÝÖá ÈßËíÑ Úáì ÓÈíá ÇáãËÇá áÇËäÊí ÚÔÑÉ äÞØÉ ÊæÒÚ ÈÇáÊÓÇæí Ýí ÌãíÚ ÃäÍÇÁ ÕæÑÉ ãä ÇáÏæÑÉ ÞÏ ÊÊÌãÚ ãÚÇ Ýí ãäØÞÉ æÇÍÏÉ ÕÛíÑÉ. æÅÐÇ áã íÍÏË åÐÇ Ýí ÍÇÌÉ Åáì ÇáßËíÑ ãä ÇáäÞÇØ áÞíÇÓ Ãæ ÃäåÇ áíÓÊ ãæÒÚÉ ÈÔßá ÌíÏ ¡ ääÕÍß ÈÃä
ÊÖíÝ æíáÝÊ ÇáäÙÑ Åáì ÇáÞíÇÓ. æßãÇ ÓÊÑæä ¡ ÓÑíÚÉ ÌÏÇ æÓåáÉ áÅÖÇÝÉ äÞÇØ ÅÖÇÝíÉ áÞíÇÓ Ðáß áÇ ÊÊÑÏÏ Ýí ÇáÞíÇã ÈÐáß.
Bundle Adjustment
ÊÚÏíá ÍÒãÉ The Bundle Adjustment is the program that processes the photographic measurements to produce the final XYZ coordinates of all the measured points.
ÝÅä ÇáÍÒãÉ ÇáÊßíÝ åæ ÈÑäÇãÌ ÇáÚãáíÇÊ ÇáÝæÊæÛÑÇÝíÉ ÞíÇÓÇÊ áÇäÊÇÌ ÇáäåÇÆí XYZ ÅÍÏÇËíÇÊ ßá äÞØÉ ÞíÇÓ. In order to do this, it must Triangulate the target points, Resect the pictures and Self-calibrate the camera.
æááÞíÇã ÈÐáß ¡ íÌÈ Ãä ËáË ÇáåÏÝ äÞØÉ ÅÓÊÃÕá ÇáÕæÑ ÇáÐÇÊí æãÚÇíÑÉ ÇáßÇãíÑÇ. The Bundle Adjustment program is called STAR, which stands for Self-Calibration, Triangulation and Resection.
ÝÅä ÇáÍÒãÉ ÊÚÏíá ÇáÈÑäÇãÌ ÇáãÓãì ÓÊÇÑ ÇáÐí íÞÝ ÇáÐÇÊí ááãÚÇíÑÉ ¡ æÇáÊËáíË ¡
æÇáÇÓÊÆÕÇá ÇáÌÒÆí.
The real power of the bundle adjustment is that it is able to do all three of these things simultaneously.
ÇáÞæÉ ÇáÍÞíÞíÉ ááÍÒãÉ ÇáÊÚÏíá Ãäå ÞÇÏÑ Úáì ÇáÞíÇã Èßá åÐå ÇáÇÔíÇÁ ÇáËáÇËÉ Ýí æÞÊ æÇÍÏ. If you review the descriptions of Triangulation and Resection, it appears there is a problem.
ÅÐÇ ßäÊ ÇÓÊÚÑÇÖ ÃæÕÇÝ ÇáÊËáíË æÇáÇÓÊÆÕÇá ÇáÌÒÆí ¡ íÈÏæ Ãä åäÇß ãÔßáÉ. In order to triangulate the measured points, we must know the orientation of the pictures.
áËáË ÇáãÞÇÓÉ äÞØÉ ¡ íÌÈ ÚáíäÇ Ãä äÚÑÝ æÌåÉ ÇáÕæÑ. However, in order to orient the pictures, we must know the coordinates of the measured points.
æãÚ Ðáß ¡ æÈÛíÉ ÊæÌíå åÐå ÇáÕæÑ ¡ áÇ
ÈÏ áäÇ ãä ãÚÑÝÉ ÇÍÏÇËíÇÊ äÞØÉ ááÞíÇÓ. How do we get started here- The answer is the bundle adjustment has the capability to figure them both out simultaneously and to self-calibrate the camera as well!
ßíÝ íãßääÇ Ãä äÈÏà åäÇ Èíä
ÇáÌæÇÈ åæ ÍÒãÉ ÇáÊßíÝ áÏíåÇ ÇáÞÏÑÉ Úáì ÇáÑÞã æÇÍÏ ãäåãÇ Ýí ÊÞÑíÑ ÇáãÕíÑ ¡
æãÚÇíÑÉ ÇáßÇãíÑÇ ÃíÖÇ! This is where the name bundle adjustment comes from because it bundles all these things together and solves them all at the same time.
åÐÇ åæ ÇÓã ÍÒãÉ ÇáÊÚÏíá áÃäå íÃÊí ãä ÍÒã ßá åÐå ÇáÃÔíÇÁ ãÚÇ ¡
æíÍá áåã ÌãíÚÇ Ýí æÞÊ æÇÍÏ.
The Bundle Adjustment does need a little help though.
ÝÅä ÍÒãÉ ÊÚÏíá ÈÍÇÌÉ ÞáíáÇ Úáì ÇáÑÛã ãä ãÓÇÚÏÉ. It must have the preliminary orientation for each photograph in order to get started.
íÌÈ Ãä íßæä ÇáÊæÌå ÇáÃæáí áßá ÕæÑÉ ãä ÃÌá ÇáÈÏÁ. This preliminary orientation is accomplished with the AutoStart or SuperStart procedures that are done for every photograph.
åÐÇ åæ ÇáÊæÌå ÇáÃæáí ÇáÐí ÃäÌÒ ãÚ ÊÔÛíá ÊáÞÇÆí Ãæ SuperStart ÇáÅÌÑÇÁÇÊ ÇáÊí ÊÊã Ýí ßá ÕæÑÉ. When STAR is finished it then produces the following:
ÚäÏãÇ ÇäÊåì ÇáäÌã Ëã íäÊÌ ãÇ íáí : 1.
1. XYZ coordinates (and accuracy estimates) for each point
XYZ ÈÊäÓíÞ (æÏÞÉ ÇáÊÞÏíÑÇÊ) áßá äÞØÉ
2.
2. The XYZ coordinates and 3 aiming angles (and accuracy estimates) for each picture.
ÝÅä XYZ ÈåÏÝ ÊäÓíÞ æÇáÒæÇíÇ 3) æÏÞÉ ÇáÊÞÏíÑÇÊ) áßá ÕæÑÉ.
3.
3. The camera calibration parameters (and their accuracy estimates).
ÇáßÇãíÑÇ ãÚÇííÑ æÇáãÚÇíÑÉ (æÏÞÉ ÇáÊÞÏíÑÇÊ). Measuring Accuracy
ÏÞÉ ÇáÞíÇÓ V-STARS in the single camera mode provides accuracies comparable to those achieved by other large volume, high accuracy coordinate measurement systems such as Digital Theodolites, Co-ordinate Measuring Machines (CMMs), and Laser Trackers.
äÌæã Ýí ÇáÎÇãÓ æÍíÏ íæÝÑ ÏÞÉ ÇáßÇãíÑÇ ØÑíÞÉ ããÇËáÉ áÊáß ÇáÊí ÍÞÞåÇ ÛíÑå ãä ÇáÍÌã ÇáßÈíÑ ¡ æÞÏÑ ßÈíÑ ãä ÇáÏÞÉ æÊäÓíÞ äÙã ÞíÇÓ ÑÞãíÉ ãËá Theodolites ¡ ÇáÅÍÏÇËí ÂáÇÊ ÞíÇÓ (CMMs) ¡ æÇááíÒÑ ÇáãÞÊÝæä. Typical accuracies are 25 to 50 microns (0.001" to 0.002") on a 3-meter (ten foot) object for the INCA2 and 50 to 100 microns (0.002" to 0.004") on a 3-meter (ten foot) object for the E3 system.
ÏÞÉ åí ÚÇÏÉ 25 Åáì 50 ãíßÑæä (0.001 "0.002") Úáì 3 ÇãÊÇÑ (ÚÔÑÉ ÇáÞÏã) åÏÝ áINCA2 æ 50 æ 100 ãíßÑæä (0.002 "0.004") Úáì 3 ÇãÊÇÑ (ÚÔÑÉ ÇáÞÏã) ááÌÓã E3 ÝÅä ÇáäÙÇã.
However, the accuracy of a photogrammetric measurement can vary significantly since accuracy depends on several inter-related factors.
æãÚ Ðáß ¡ ÝÅä ÏÞÉ ÇáãÓÍ ÇáÊÕæíÑí ááÞíÇÓ íãßä Ãä ÊÎÊáÝ ÇÎÊáÇÝÇ ßÈíÑÇ ãäÐ ÇáÏÞÉ íÊæÞÝ Úáì ÚÏÉ ÚæÇãá ãÊÑÇÈØÉ. The most important are:
ÃåãåÇ :
1.
1. The resolution (and quality) of the camera you are using,
ÇáÞÑÇÑ (æÇáÌæÏÉ) ááßÇãíÑÇ ßäÊ ÊÓÊÎÏã ¡ 2.
2. The size of the object you're measuring,
ÍÌã ÇáÌÓã ßäÊ ÞíÇÓ ¡ 3.
3. The number of photographs you're taking, and
ÚÏÏ ÇáÕæÑ ßäÊ ÃÎÐ æ
4.
4. The geometric layout of the pictures relative to the object and to each other.
ÇáÊÕãíã ÇáåäÏÓí ááÕæÑ ÈÇáäÓÈÉ ááãæÖæÚ æÈÚÖåÇ ÇáÈÚÖ.
The diagram below illustrates the effects of the four factors and their influence on accuracy.
æíæÖÍ ÇáÑÓã ÇáÈíÇäí ÃÏäÇå ÂËÇÑ ÇáÚæÇãá ÇáÃÑÈÚÉ æÊÃËíÑåÇ Úáì ÇáÏÞÉ.
The diagram represents a pyramid with the four factors at the base of the pyramid and high accuracy at the top of the pyramid.
ÇáÑÓã íãËá ÇáåÑã ãÚ ÇáÚæÇãá ÇáÃÑÈÚÉ Ýí ÞÇÚÏÉ ÇáåÑã æÇáÏÞÉ ÇáÚÇáíÉ Ýí ÃÚáì ÇáåÑã. To get higher accuracy ( a higher pyramid) you need more of the items shown on the lines of the pyramid (higher resolution, smaller size, more photos, and wider, but not too wide, geometry).
ááÍÕæá Úáì ÏÞÉ ÃÚáì (ÃÚáì ÇáåÑã) æÊÍÊÇÌ Åáì ãÒíÏ ãä ÇáÈäæÏ ÇáãÈíäÉ Úáì ÎØæØ ÇáåÑã (ÃÚáì ÇáÞÑÇÑ ¡ ÈÍÌã ÃÕÛÑ ¡ æÃßËÑ ãä ÇáÕæÑ ¡ æÚáì äØÇÞ ÃæÓÚ ¡ æáßä áíÓ Úáì äØÇÞ æÇÓÚ ÌÏÇ ¡ æÇáåäÏÓÉ). See Appendix A. - "How Accurate is V-STARS?"
ÇäÙÑ ÇáãáÍÞ Ã
-- "ãÏì ÏÞÉ åæ ÇáÎÇãÓ ÓÊÇÑÒ¿" Scaling Photogrammetry
ÍÌã ÇáÊÕæíÑí Photogrammetric measurements are inherently dimensionless.
ÇáãÓÍ ÇáÊÕæíÑí ÞíÇÓ ÃÈÚÇÏ åí ÈØÈíÚÊåÇ. An example of this is shown below.
ãËÇá Úáì Ðáß åæ ãÈíä ÃÏäÇå. The picture of the first car could be a picture of a full-size car or of a matchbox model; there is no way to tell. However, if we know the size of something that is also in the picture, we can now say something about the size of the car.
ÇáÕæÑÉ ÇáÃæáì ááÓíÇÑÉ íãßä Ãä íßæä ÕæÑÉ ßÇãáÉ ÈÍÌã ÓíÇÑÉ ¡
Ãæ ãä ÚáÈÉ ÇáËÞÇÈ ÇáäãæÐÌ æáíÓ åäÇß ãä ÓÈíá áãÚÑÝÉ æáßä ÅÐÇ ßÇä áäÇ Ãä äÚÑÝ ÍÌã ãÇ åæ ÃíÖÇ Ýí ÇáÕæÑÉ ¡ íãßääÇ
ÇáÂä Ãä ÃÞæá ÔíÆÇ Úä ÍÌã ÇáÓíÇÑÉ. (Theodolites are another inherently dimensionless technology).
(ÂÎÑ Theodolites ÈØÈíÚÊåÇ ÃÈÚÇÏ ÇáÊßäæáæÌíÇ). To scale a photogrammetric measurement, we must have at least one known distance. If we know the actual coordinates beforehand of some targeted points, we can compute the distances between these points and use these to scale the measurement.
æåæ ãÞíÇÓ áÞíÇÓ ÇáãÓÍ ÇáÊÕæíÑí ¡ æíÌÈ Ãä íßæä áÏíäÇ æÇÍÏÇ Úáì ÇáÇÞá íÚÑÝ ÈÚÏ. æÅÐÇ ßäÇ äÚÑÝ ãÓÈÞÇ ÇáÝÚáíÉ íäÓÞ ÈÚÖ ÇáäÞÇØ ÇáãÓÊåÏÝÉ ¡ íãßääÇ
ÈÍÓÇÈ ÇáãÓÇÝÇÊ Èíä åÐå ÇáäÞÇØ æÊæÓíÚ äØÇÞ ÇÓÊÎÏÇã åÐå ÇáÞíÇÓ. Another possibility is to use a fixture with targets on it and measure this along with the object.
æåäÇß ÅãßÇäíÉ ÃÎÑì ÊÊãËá Ýí ÇÓÊÎÏÇã áÇÚÈÇ ÇÓÇÓíÇ ãÚ ÇáÃåÏÇÝ æÞíÇÓ åÐÇ ÌäÈÇ Åáì ÌäÈ ãÚ æÌæå. The distance between the targets on the bar is known and can be used to scale the measurement. Such fixtures are commonly called scale bars.
ÇáãÓÇÝÉ Èíä ÇáÃåÏÇÝ Úáì ÔÑíØ ãÚÑæÝ æíãßä ÇÓÊÎÏÇãåÇ áÞíÇÓ ÍÌã åÐå ÇáÊÑßíÈÇÊ ÈÔßá ÔÇÆÚ Úáì äØÇÞ æÏÚÇ ÇáÞÖÈÇä. See also Attaching the Scale Bar (s), and the questions in Appendix A regarding scale.
ÇäÙÑ ÃíÖÇ ÇáÌÏæá Êæáì ÈÇÑ (Þ) ¡ æÇáÃÓÆáÉ ÇáæÇÑÏÉ Ýí ÇáÊÐííá ÃáÝ ÈÔÃä ÇáÌÏæá.
Multiple Scale Distances
ãÊÚÏÏÉ ÌÏæá ÇáãÓÇÝÇÊ Whenever possible, you should use more than one distance to scale the measurement.
ßáãÇ ßÇä Ðáß ããßäÇ ¡ íÌÈ ÇÓÊÎÏÇã ÃßËÑ ãä æÇÍÏ áãÓÇÝÉ äØÇÞ ÇáÞíÇÓ. V-STARS combines the individual scale measurements to provide higher scale accuracy.
ÇáÎÇãÓ ÓÊÇÑÒ íÌãÚ ÇáÝÑÏ ÞíÇÓÇÊ ÇáÍÌã áÊæÝíÑ ÃÚáì ÏÞÉ ÇáÍÌã. More importantly, this allows you to find scale errors.
æÇáÃåã ãä Ðáß ¡ íÓãÍ áß åÐÇ ÇáäØÇÞ ááÚËæÑ Úáì ÇáÃÎØÇÁ. This is important because when a single scale distance is used and it is in error, the entire measurement will be incorrectly scaled. On the other hand, if you have multiple scale distances, scale errors can be detected and removed.
æåÐÇ ÃãÑ ãåã áÇäå ÚäÏãÇ Êßæä Úáì ãÓÇÝÉ æÇÍÏÉ æíÓÊÎÏã Úáì äØÇÞ æÃäå ãä ÇáÎØà ¡ ßáå ÛíÑ ÕÍíÍ æÓíÊã ÞíÇÓ ãÓÊæì. æãä
ÌåÉ ÃÎÑì ¡ ÅÐÇ ßÇä áÏíß ãÞíÇÓ ãÓÇÝÇÊ ãÊÚÏÏÉ ¡ æÍÌã ÇáÃÎØÇÁ ÇáÊí íãßä Ãä ÊßÔÝ æÅÒÇáÊåÇ. With two known distances, if one is in error you will be able to detect a scale error but usually you cannot tell which one is in error.
ãÚ ÇËäíä ãä íÚÑÝ ÇáãÓÇÝÇÊ ¡ æÅÐÇ ãÇ ÇáÎØà ÓÊßæä ÞÇÏÑÇ Úáì ßÔÝ ÍÌã ÇáÎØà æáßä ÚÇÏÉ ãÇ áÇ ÊÓÊØíÚ Çä ÊÞæá ãä åæ ÇáÎØÃ. (Sometimes, though, you can tell by inspecting the scale points).
(æÝí ÈÚÖ ÇáÃÍíÇä ¡ æÅä ßÇä íãßäß ÇáÞæá Úä ØÑíÞ äÞØÉ ÊÝÊíÔ ÇáÌÏæá). With three known scale distances, you can usually detect if one of them is in error and remove it.
ãÚ ËáÇËÉ ãä ÇáãÚÑæÝ Úáì äØÇÞ ÇáãÓÇÝÇÊ ¡ íãßäß
ÚÇÏÉ ãÇ ÇÐÇ ßÇä ÇáßÔÝ Úä æÇÍÏ ãäåã Ýí ÇáÎØà æÇÒÇáÊå. When scale bars are used, one good technique is to use a bar that has more than two targets.
ÚäÏãÇ ÊÓÊÎÏã Úáì äØÇÞ æÇáÍÇäÇÊ ¡ æÇÍÏÉ ÌíÏÉ áÇÓÊÎÏÇã åÐå ÇáÊÞäíÉ ÍÇäÉ Ãä ÃßËÑ ãä åÏÝíä. Another technique is to use more than one scale bar.
ÃÓáæÈ ÂÎÑ íÊãËá Ýí ÇÓÊÎÏÇã ÃßËÑ ãä ÌÏæá äÞÇÈÉ ÇáãÍÇãíä. Alternatively, you can use both techniques.
ÈÏáÇ ãä Ðáß ¡ íãßäß ÇÓÊÎÏÇã ÇáÊÞäíÇÊ Úáì ÍÏ ÓæÇÁ. It is up to you, but, whenever possible, you should use multiple scale distances.
æÇáÃãÑ ãÊÑæß áßã ¡ æáßä ¡ ßáãÇ ßÇä Ðáß ããßäÇ ¡ íÌÈ Úáíß ÇÓÊÎÏÇã ãÞíÇÓ ãÓÇÝÇÊ ãÊÚÏÏÉ. Long Scale Distances
ÌÏæá ÇáãÓÇÝÇÊ ÇáØæíáÉ The scale distance(s) should be as long as practical because any inaccuracy in the scale distance(s) is magnified by the proportion of the size of the object to the scale distance.
ÍÌã ÇáãÓÇÝÉ (Þ) íäÈÛí Ãä Êßæä ãÇ ÏÇãÊ ÇáÚãáíÉ áÃä Ãí ÚÏã ÏÞÉ Ýí ÍÌã ÇáãÓÇÝÉ (Þ) ÊÊÖÎã ÈÝÚá äÓÈÉ ÍÌã ÇáÌÓã áÍÌã ÇáãÓÇÝÉ. For example, if a one meter (40") scale distance is used on a 10 meter (400") object, and the scale distance has 0.1 mm (0.004") of error, then the object will have ten times this error, or 1mm (0.040").
Úáì ÓÈíá ÇáãËÇá ¡ ÅÐÇ ßÇä ãÊÑ æÇÍÏ (40 ") Úáì äØÇÞ æíÓÊÎÏã Úáì ãÓÇÝÉ 10 ãÊÑÇ (400") æÌæå ¡ æÍÌã ÇáãÓÇÝÉ 0.1 ãáã (0.004 ") ááÎØà ¡ æÈÚÏ Ðáß Óíßæä ãæÖæÚ ÚÔÑÉ ÃÖÚÇÝ åÐÇ ÇáÎØà ¡ Ãæ 1mm (0.040 ").
In some cases, a measurement may not need to be precisely scaled.
Ýí ÈÚÖ ÇáÍÇáÇÊ ¡ áÇ íÌæÒ ÞíÇÓ ÊÍÊÇÌ Åáì ãÓÊæì ãä ÇáÏÞÉ. For example, some surface or shape measurements do not require accurate scale.
Úáì ÓÈíá ÇáãËÇá ¡ ÈÚÖ ÇáÞíÇÓÇÊ ÇáÓØÍíÉ Ãæ ÇáÔßá áÇ ÊÊØáÈ ÏÞÉ æÇÓÚ. In this case, you can use nominal distances to provide scale or you can use the AutoBar for scale. However, the AutoBar is too small to accurately scale a measurement.
Ýí åÐå ÇáÍÇáÉ ¡ íãßäß
ÇÓÊÎÏÇã ÇÓãí áÊæÝíÑ ãÞíÇÓ ÇáãÓÇÝÇÊ Ãæ íãßäß ÇÓÊÎÏÇã áAutoBar ÇÓÚ. æãÚ Ðáß ¡ ÝÅä AutoBar ÕÛíÑ ááÛÇíÉ áÞíÇÓ ÏÞíÞ ÇáÍÌã.
Measuring
ÞíÇÓ Measuring with V-STARS
ÞíÇÓ ÇáÎÇãÓ ãÚ ÇáäÌæã No matter what kind of measurement you are doing, measuring with V-STARS usually consists of the following steps.
ÈÛÖ ÇáäÙÑ Úä äæÚ ãä ÇáÞíÇÓ ÊÞæãæä Èå ¡ ãÚ ÞíÇÓ ÇáÎÇãÓ ÓÊÇÑÒ ÚÇÏÉ ãä ÇáÎØæÇÊ ÇáÊÇáíÉ. 1.
1. Planning the Measurement
ÇáÊÎØíØ ÈÞíÇÓ 2.
2. Targeting the Object
ÇÓÊåÏÇÝ ßÇÆä 3.
3. Taking Pictures
ÇáÊÞÇØ ÇáÕæÑ 4.
4. Measuring Pictures
ÞíÇÓ ÇáÕæÑ 5.
5. Processing Pictures (to get 3-dimensional coordinates)
ãÚÇáÌÉ ÇáÕæÑ (3) ááÍÕæá Úáì ÇáÃÈÚÇÏ æíäÓÞ) 6.
6. Analyzing the Results (manipulating the results to help check and visualize the results)
ÊÍáíá ÇáäÊÇÆÌ (ÇáÊáÇÚÈ Ýí ÇáäÊÇÆÌ ááãÓÇÚÏÉ Ýí ÇáÊÍÞÞ ãä ÇáäÊÇÆÌ æÊÕæÑ)
The list above is a general guide. However, every measurement project is different, and therefore the content and even sometimes the order of the steps given above may be different depending on the project requirements and sometimes operator preference. For example, on some projects, you will take all pictures first (to minimize time on-site typically) and then measure them, while on others you will measure each picture after it is taken.
ÇáÞÇÆãÉ ÃÚáÇå åæ ÇáãÑÔÏ ÇáÚÇã ¡ ÅáÇ Ãä ßá ãÔÑæÚ ÞíÇÓ ãÎÊáÝÉ ¡ æÈÇáÊÇáí ÝÅä ãÖãæä æÍÊì Ýí ÈÚÖ ÇáÃÍíÇä ÊÑÊíÈ ÇáÎØæÇÊ ÇáãÐßæÑÉ ÃÚáÇå ÞÏ Êßæä ãÎÊáÝÉ ÊÈÚÇ áÇÍÊíÇÌÇÊ ÇáãÔÑæÚ ¡
æÃÍíÇäÇ ÊÝÖíá ÇáãÔÛá ¡ ÝÚáì ÓÈíá
ÇáãËÇá ¡ Úáì ÈÚÖ ÇáãÔÇÑíÚ ¡ ÓæÝ ÊÊÎÐ ßÇÝÉ ÇáÕæÑ ÇáÃæáì (ááÊÞáíá ãä ÇáæÞÊ Úáì ÇáãæÞÚ ÚÇÏÉ) ¡ Ëã ÞíÇÓåÇ ¡ Ýí
Ííä Ãä ÇáÂÎÑíä ÓæÝ ÞíÇÓ ßá ÕæÑÉ æÈÚÏ Ãä ÇÊÎÐÊ. On other projects, you will take and measure some pictures, and then process them to get preliminary results so you can make measuring the remaining pictures easier.
Úáì ÛíÑåÇ ãä ÇáãÔÇÑíÚ ¡ ÓæÝ ÊÃÎÐ æÞíÇÓ ÈÚÖ ÇáÕæÑ ¡ Ëã ÊÌåíÒåÇ ááÍÕæá Úáì ÇáäÊÇÆÌ ÇáÃæáíÉ ÍÊì ÊÊãßä ãä ÊÞÏíã ãÇ ÊÈÞì ãä ÞíÇÓ ÇáÕæÑ ÃÓåá. Still, all the steps listed above are carried out in some fashion on every project.
æãÚ Ðáß ¡ ÌãíÚ ÇáÎØæÇÊ ÇáãÐßæÑÉ ÃÚáÇå æÊÌÑí Úáì äÍæ ãÇ Ýí ßá ãÔÑæÚ. Each of these steps is described in detail in the following chapters.
ßá ÎØæÉ ãä åÐå ÇáÎØæÇÊ ÈÇáÊÝÕíá Ýí ÇáÝÕæá ÇáÊÇáíÉ.
Planning the Measurement
ÇáÊÎØíØ ÈÞíÇÓ Proper planning is essential for making a successful measurement.
áÇ ÈÏ ãä ÇáÊÎØíØ ÇáÓáíã áÊÍÞíÞ ÇáäÌÇÍ Ýí ÇáÞíÇÓ. This is especially true if the measurement is complex or if it is the first time, you have done this particular type of measurement.
æíäØÈÞ Ðáß ÈÕÝÉ ÎÇÕÉ ÅÐÇ ßÇä ÞíÇÓ ãÚÞÏÉ ¡
Ãæ ÅÐÇ ßÇäÊ åÐå åí ÇáãÑÉ ÇáÃæáì ¡ æÇáÐí ÞãÊã Èå Ýí åÐÇ ÇáäæÚ ãä ÇáÞíÇÓ. To plan properly, you must have information about the measurement.
Úáì ÇáÊÎØíØ ÈÇáÔßá ÇáãäÇÓÈ ¡ æíÌÈ Ãä íßæä áÏíß ãÚáæãÇÊ Úä ÇáÞíÇÓ. Use the following list of questions to help you plan the measurement.
ÇÓÊÎÏÇã ÞÇÆãÉ ÇáãÓÇÆá ÇáÊÇáíÉ áãÓÇÚÏÊß Úáì ÎØÉ ÞíÇÓ. Questions You Should Ask: Remember "V-STARS"
ÇáÃÓÆáÉ ÇáÊí íÌÈ Úáíß Ãä ÊÓÃá : ÊÐßÑ "ãä ÇáÎÇãÓ ÓÊÇÑÒ" V isibility - Can the points of interest on the object be seen?
ÎÇãÓÇ isibility -- åá äÞÇØ ÇáÝÇÆÏÉ Úáì Ãä íäÙÑ Åáì æÌæå¿ Remember that V-STARS is a "line of sight" technology based on triangulation.
ÊÐßÑ Ãä ãä ÇáÎÇãÓ ÓÊÇÑÒ åæ "ÎØ ÇáÑÄíÉ" ÇáÞÇÆãÉ Úáì ÇáÊßäæáæÌíÇ ÇáãËáËÇÊ. That means the points must be seen from at least two different locations to be measured.
æåÐÇ íÚäí Çä äÞÇØ íÌÈ Ãä íäÙÑ Åáíå ãä ÇËäíä Úáì ÇáÃÞá ãä ãæÇÞÚ ãÎÊáÝÉ ááÞíÇÓ. For higher accuracy, the points should be seen from very different locations and from more than just two locations.
ÃÚáì ÏÞÉ ¡ æÇáäÞÇØ ÇáÊí íäÈÛí Ãä íäÙÑ ÅáíåÇ ãä ãæÇÞÚ ãÎÊáÝÉ ÌÏÇ æÃßËÑ ãä ãÌÑÏ ãæÞÚíä. (See Measuring Accuracy for more details on how geometry and the number of photos affect accuracy).
(ÇäÙÑ ÞíÇÓ ÏÞÉ áãÒíÏ ãä ÇáÊÝÇÕíá Íæá ßíÝíÉ ÇáåäÏÓÉ æÚÏÏ ãä ÇáÕæÑ íÄËÑ Úáì ÏÞÉ).
Also, remember that V-STARS never measures the points of interest directly.
ÃíÖÇ ¡ ÊÐßÑ Ãä ãä ÇáÎÇãÓ ÓÊÇÑÒ ÃÈÏÇ ÇáÊÏÇÈíÑ äÞÇØ ÇáÇåÊãÇã ÈÔßá ãÈÇÔÑ. Instead, V-STARS measures retro-reflective targets that are placed on, or in a known relationship to, the points of interest.
æÈÏáÇ ãä ÇáÎÇãÓ ÓÊÇÑÒ ÇáÊÏÇÈíÑ ÚÇßÓÉ ááÃåÏÇÝ ÇáÊí æÖÚÊ ¡ Ãæ Ýí ÚáÇÞÉ ãÚÑæÝÉ ¡ æÇáäÞÇØ ÇáãËíÑÉ ááÇåÊãÇã. If a point of interest cannot be seen directly, often some form of offset target can be devised to measure the point indirectly.
ÅÐÇ ßÇäÊ äÞØÉ ÇáÇåÊãÇã áÇ íãßä Ãä íäÙÑ Åáíå ãÈÇÔÑÉ ¡ æßËíÑÇ ãÇ Êßæä ÔßáÇ ãä ÃÔßÇá ÇáÊÚæíÖ Úä ÇáåÏÝ æíãßä æÖÚåÇ áÞíÇÓ ÏÑÌÉ ÛíÑ ãÈÇÔÑÉ.
S ize and Shape - What is the size and shape of the object?
ÏÅ ize æÇáÔßá -- ãÇ åæ ÍÌã ÇáÌÓã æÔßáå¿ The size and shape (convex, concave, single-sided, multiple sided, etc.) will determine how complex the measurement will be, how much room you will need around the object, and the level of accuracy you can obtain.
ÍÌã æÔßá (ãÍÏÈ ¡ ãÞÚÑ ¡ ãä
ÌÇäÈ æÇÍÏ ¡ ãä ÌÇäÈ æãÊÚÏÏÉ ¡ æÛíÑ Ðáß) æÓæÝ íÍÏÏ ßíÝíÉ ÞíÇÓ ãÚÞÏÉ Óíßæä ÍÌã ÇáÛÑÝÉ ÓæÝ ÊÍÊÇÌ Ýí ÌãíÚ ÃäÍÇÁ ÇáÌÓã ¡ æãÓÊæì ãä ÇáÏÞÉ íãßäß ÇáÍÕæá ÚáíåÇ. The size and shape will also determine what type and size of targets will be used.
ÍÌã æÔßá ÃíÖÇ ÊÍÏíÏ äæÚ æÍÌã ÇáÃåÏÇÝ ÇáÊí ÓæÝ ÊÓÊÎÏã.
T argeting - Can the points of interest on the object be targeted?
Êí argeting -- åá äÞÇØ ÇáÇåÊãÇã Úáì ãæÖæÚ ÇÓÊåÏÇÝ¿ If they cannot, you must use another method (V-STARS in the multiple camera mode using the touch probe for example, See the V-STARS/M manual for details). Targeting the object to obtain the measurements you desire can often be one of the most challenging and time consuming aspects of a project. See Targeting for more information.
ÅÐÇ áÇ íãßä ¡ íÌÈ ÇÓÊÎÏÇã ØÑíÞÉ ÃÎÑì (ÇáÎÇãÓ ÇáãÊÚÏÏÉ äÌæã Ýí ØÑíÞÉ ÇÓÊÎÏÇã ÇáßÇãíÑÇ áãÓÉ ÇáÊÍÞíÞ Úáì ÓÈíá ÇáãËÇá ¡ ÇäÙÑ ÇáÎÇãÓ ÓÊÇÑÒ / ã ÇáíÏæíÉ ááÍÕæá Úáì ÇáÊÝÇÕíá). ãæÖæÚ ÇáÇÓÊåÏÇÝ ááÍÕæá Úáì ÇáÞíÇÓÇÊ ÇáÊí ÊÑíÏåÇ íãßä Ýí ßËíÑ ãä ÇáÃÍíÇä æÇÍÏÉ ãä ÃÕÚÈ æÊÓÊÛÑÞ æÞÊÇ ØæíáÇ ãä ÌæÇäÈ ÇáãÔÑæÚ. ÇáÇÓÊåÏÇÝ ÇäÙÑ áãÒíÏ ãä ÇáãÚáæãÇÊ.
A ccuracy - What level of accuracy is desired or required?
æÞÇá ccuracy -- ãÇ åæ ãÓÊæì ãä ÇáÏÞÉ ÇáãäÔæÏ Ãæ ÇáãØáæÈ¿ Notice the terms desired and required are both used.
ÇáÅÔÚÇÑ ÇáãØáæÈ æÇáÔÑæØ ÇáãØáæÈÉ áßá ãä íÓÊÎÏã. It is important to distinguish what level of accuracy is wanted and what level of accuracy is acceptable.
ãä ÇáÃåãíÉ ÈãßÇä ÇáÊãííÒ Èíä ãÇ åæ ãÓÊæì ãä ÇáÏÞÉ æíÑíÏ Ãí ãÓÊæì ãÞÈæá ãä ÇáÏÞÉ. Taking more pictures can increase photogrammetric accuracy significantly.
æÇÊÎÇÐ ÇáãÒíÏ ãä ÇáÕæÑ íãßä Ãä íÒíÏ ÈÔßá ßÈíÑ ãä ÏÞÉ ÇáãÓÍ ÇáÊÕæíÑí. It is important to realize that this accuracy improvement will reach a diminishing point of return.
æãä Çáãåã Ãä äÏÑß Ãä åÐÇ ÇáÊÍÓä ÓæÝ ÊÕá ÏÞÊåÇ ÊÞáíÕ äÞØÉ ÇáÚæÏÉ. This tradeoff must be considered when deciding how many photographs to take.
åÐå ÇáãÞÇíÖÉ æíÌÈ ÇáäÙÑ ÝíåÇ ÚäÏ ÇáÈÊ Ýí ßíÝíÉ ÇÊÎÇÐ ÇáÚÏíÏ ãä ÇáÕæÑ ÇáÝæÊæÛÑÇÝíÉ. See Measuring Accuracy for more details on the factors (including the number of photographs) that affect accuracy.
ÞíÇÓ ÏÞÉ ÇäÙÑ áãÒíÏ ãä ÇáÊÝÇÕíá Úä ÇáÚæÇãá (ÈãÇ Ýí Ðáß ÚÏÏ ãä ÇáÕæÑ ÇáÝæÊæÛÑÇÝíÉ) ÇáÊí ÊÄËÑ Ýí ÏÞÉ.
It is also important to define the level of accuracy in a clear and unambiguous way.
æãä Çáãåã ÃíÖÇ áÊÍÏíÏ ãÓÊæì ÇáÏÞÉ Ýí æÇÖÍÉ áÇ áÈÓ ÝíåÇ. There are many ways of specifying accuracy.
åäÇß ØÑÞ ÚÏíÏÉ áÊÍÏíÏ ÇáÏÞÉ. For example, is the accuracy specified an absolute range (meaning no value should be outside the entire range) or is it an RMS value (meaning, on average, 67% of the values will be within plus or minus the accuracy specification).
Úáì ÓÈíá ÇáãËÇá ¡ ÊÍÏÏ ÈÏÞÉ ãØáÞÉ ãÌãæÚÉ (Çí áÇ íÌÈ Ãä Êßæä ÇáÞíãÉ ÎÇÑÌ ÇáãÌãæÚÉ ÇáßÇãáÉ) Ãã Ãäå äÙÇã ÅÏÇÑÉ ÇáãæÇÑÏ ÇáÞíãÉ (Ãí ¡ Ýí
ÇáãÊæÓØ ¡ 67 ٪
ãä ÇáÞíã ÇáÊí ÓÊßæä Ýí ÍÏæÏ ÒÇÆÏ Çæ äÇÞÕ ÏÞÉ ÇáãæÇÕÝÇÊ).
R oom - How much room is there around the object?
oom Ó -- ßíÝ Ãä åäÇß ãÌÇáÇ ßÈíÑÇ Ýí ÌãíÚ ÃäÍÇÁ ÇáÌÓã¿ This question relates to visibility again.
åÐÇ ÇáÓÄÇá íÊÚáÞ ÇáÑÄíÉ ãä ÌÏíÏ. The amount of room around the object will determine if the project is even feasible, and if it is, will determine to some extent the number of photographs you take.
ãÞÏÇÑ ÛÑÝÉ Ýí ÌãíÚ ÃäÍÇÁ ÇáÌÓã ÓæÝ ÊÍÏÏ ãÇ ÅÐÇ ßÇä ÇáãÔÑæÚ ÍÊì Ããßä ¡ æÅÐÇ ßÇä Ðáß ¡ æÓæÝ ÊÍÏÏ Åáì ÍÏ ãÇ ãä ÚÏÏ ÇáÕæÑ ÇáÊí ÊÃÎÐåÇ. Remember that for the standard medium angle lens provide with V-STARS, the rule of thumb is you will see about as much of the object as your distance back from the object. For example, if you are 3 meters from the object you can see about 3 meters of the object.
áäÊÐßÑ Ãä ÇáãÚíÇÑ ÇáãÊæÓØ ÒÇæíÉ ÇáÚÏÓÉ ÊÞÏíã ÇáÎÇãÓ ãÚ ÇáäÌæã ¡ æÈÍßã ÇáÊÌÑÈÉ åæ ÓÊÑæä Úä ÞÏÑ ãä ÃæÌå áßã ÇáãÓÇÝÉ ãä ÇáÌÓã ¡ ÝÚáì ÓÈíá
ÇáãËÇá ¡ ÅÐÇ ßäÊ 3 ÇãÊÇÑ ãä æÌæå ÊÑæä ÍæÇáí 3 ÃãÊÇÑ ãä ÇáÌÓã. If there is not enough room to see the entire object in the photograph, you can still measure the object by photographing it in overlapping sections (this technique is called mosaicing) but this makes the measurement more complicated.
ÅÐÇ áã Êßä åäÇß ãÓÇÍÉ ßÇÝíÉ áÑÄíÉ æÌæå ßÇãá Ýí ÇáÕæÑÉ ¡ áÇ íÒÇá ÈÅãßÇäß
ÞíÇÓ Ðáß Úä ØÑíÞ ÊÕæíÑ æÌæå ãÊÏÇÎáÉ Ýí ÇáÝÑæÚ (æÊÓãì åÐå ÇáÊÞäíÉ mosaicing) æáßä åÐÇ íÌÚá ÞíÇÓ ÃßËÑ ÊÚÞíÏÇ.
S cale - Will scale be used?
cale Ï Å -- åá ÊÓÊÎÏã Úáì äØÇÞ¿ If so, how will it be applied to the object?
ÅÐÇ ßÇä ÇáÃãÑ ßÐáß ¡ ÝßíÝ Óíßæä Úáíå Ãä íØÈÞ Úáì ãæÖæÚ¿ Although this may seem a bit trivial at first, figuring out where to put the scale bar(s) so they do not block targets or are themselves blocked can be one of the more challenging aspects of a measurement.
Úáì ÇáÑÛã ãä Ãä åÐÇ ÞÏ íÈÏæ ÊÇÝåÇ ÞáíáÇ Ýí ÇáÈÏÇíÉ ¡ ÍíË ßÔÝ áæÖÚ ÌÏæá ÇáÚÇÑÖÉ (Þ) ÍÊì áÇ íÓÊåÏÝ ÚÑÞáÉ Ãæ åí Ýí ÍÏ ÐÇÊåÇ íãßä Ãä Êßæä ãäÚÊ æÇÍÏÉ ãä ÃßËÑ ÊÍÏíÇ ÌæÇäÈ ÞíÇÓ. Add in the fact that it is desirable to have the scale bar be about the length of the object you are measuring, and that it must be rigidly attached to the object, and that if scale is important then we recommend using multiple scale distances, and this seemingly trivial task can sometimes be downright daunting.
ÃÖíÝ Ýí Ãä ãä ÇáãÓÊÍÓä Ãä íßæä ÍÌã ÔÑíØ íßæä Øæá ÇáÌÓã Çäß ÞíÇÓ ¡ æÇäåÇ íÌÈ Çä Êßæä ÕÇÑãÉ ÊÚáÞ Úáì æÌæå ¡ æÃäå ÅÐÇ ßÇä ãÞíÇÓ ãåã Ëã äæÕí ÈÇÓÊÎÏÇã ãÞíÇÓ ãÓÇÝÇÊ ãÊÚÏÏÉ ¡ åÐå ÇáãåãÉ ÇáÊí ÊÈÏæ ÊÇÝåÉ ÞÏ Êßæä ÃÍíÇäÇ ÈÕÑÇÍÉ ãÑæÚÉ. See Scaling Photogrammetry, and the questions on scale in Appendix A.
ÇäÙÑ ÇáÞíÇÓ ÇáÊÕæíÑí ¡ æÃÓÆáÉ Úä ÇáÍÌã Ýí ÇáÊÐííá ÃáÝ. Defining a Coordinate System
ÊÍÏíÏ ÊäÓíÞ äÙÇã All coordinate measurement systems must use some working coordinate system.
ÊäÓíÞ ÌãíÚ ÃäÙãÉ ÞíÇÓ æíÌÈ Ãä äÓÊÎÏã ÈÚÖ ÊäÓíÞ Úãá ÇáäÙÇã. V-STARS automatically defines a local coordinate system that uses the coordinate system defined by the first picture you measure. If the AutoBar is used, the V-STARS measurement is in the coordinate system defined by the AutoBar.
ÇáÎÇãÓ ÓÊÇÑÒ ÊáÞÇÆíÇ íÚÑÝ ÇáãÍáíÉ ÊäÓíÞ ÇáäÙÇã ÇáÐí íÓÊÎÏã äÙÇã ÊäÓíÞ ÍÏÏÊå Ãæá ÕæÑÉ áß ÞíÇÓ ÇÐÇ AutoBar íÓÊÎÏã ¡ ãä ÇáÎÇãÓ ÓÊÇÑÒ ÇáÞíÇÓ Ýí ÊäÓíÞ ÇáäÙÇã ÇáÐí ÍÏÏÊå AutoBar. This is shown in the adjacent image.
åÐÇ åæ ãÈíä Ýí ÇáÕæÑÉ ÇáãÌÇæÑÉ. If an AutoBar is not used, V-STARS uses the coordinates system on the driver file you have selected.
ÅÐÇ áã íÓÊÎÏã AutoBar ¡ ÇáÎÇãÓ ÓÊÇÑÒ íÓÊÎÏã äÙÇã ÇáÅÍÏÇËíÇÊ Úáì ÓÇÆÞ ÇáãáÝ ÇáÐí ÇÎÊÑÊå. In either case, all the images and measurements are then defined in the local coordinate system.
Ýí ßáÊÇ ÇáÍÇáÊíä ¡ ÝÅä ÌãíÚ ÇáÕæÑ æÇáÞíÇÓÇÊ Ëã ÇáãÍÏÏÉ Ýí äÙÇã ÊäÓíÞ ÇáãÍáíÉ. Typically, this local system is not usually the final coordinate system desired by the user.
æÚÇÏÉ ¡ ÝÅä
åÐÇ ÇáäÙÇã áíÓ ÇáãÍáíÉ ÚÇÏÉ ÊäÓíÞ ÇáäÙÇã ÇáäåÇÆí ÇáãäÔæÏ ãä ÞÈá ÇáãÓÊÎÏã. Your plan must include a way to define the user coordinate system you desire.
æíÌÈ Ãä ÊÔãá ÇáÎØÉ ÇáÎÇÕÉ Èß æÓíáÉ áÊÍÏíÏ æÊäÓíÞ äÙÇã ÇáãÓÊÎÏãíä ÇáÊí ÊÑíÏåÇ. In some cases, the local coordinate system defined by V-STARS is sufficient.
Ýí ÈÚÖ ÇáÍÇáÇÊ ¡ ÇáãÍáíÉ ÊäÓíÞ äÙÇã ÊÍÏÏå ÇáÎÇãÓ ÓÊÇÑÒ ßÇÝíÉ. In other cases, you must transform this local system into the desired user coordinate system.
æÝí ÍÇáÇÊ ÃÎÑì ¡ íÌÈ ÊÍæíá åÐÇ ÇáãÍáíÉ Åáì äÙÇã ÇáãÓÊÎÏã ÇáãØáæÈ ÊäÓíÞ ÇáäÙÇã. This transformation can be automatically done for you by V-STARS using design data, or you can use the WINTRANS program provided with V-STARS.
åÐÇ ÇáÊÍæá áÇ íãßä ÇáÞíÇã Èå ÊáÞÇÆíÇ áß ÞÈá ÇáÎÇãÓ ÓÊÇÑÒ ÈÇÓÊÎÏÇã ÈíÇäÇÊ ÇáÊÕãíã ¡ Ãæ íãßäß ÇÓÊÎÏÇã ÈÑäÇãÌ WINTRANS ÊÒæíÏ ÇáÎÇãÓ ÇáäÌæã. Often, the user coordinate system is defined by a subset of the measured points that have coordinates in the user's desired coordinate system.
Ýí ßËíÑ ãä ÇáÃÍíÇä ¡ ááãÓÊÎÏã ÊäÓíÞ äÙÇã ÊÍÏÏå ãÌãæÚÉ ÝÑÚíÉ ãä ÇáäÞÇØ ÇáÊí ÊÞÇÓ Ýí ÇáÅÍÏÇËíÇÊ ÇáãÓÊÎÏã ÇáãØáæÈ ÊäÓíÞ ÇáäÙÇã. These points may consist of precisely made tooling targets that are located in bushed holes, or they may be defined by features on the measured object (such as part edges, or hole locations or intersections of lines, planes, etc.) that are targeted in some way.
åÐå ÇáäÞÇØ íãßä Ãä ÊÊÃáÝ ãä ÇáÃåÏÇÝ ÈÏÞÉ ÊÞÏã ÇáÃÏæÇÊ ÇáÊí ÊæÌÏ Ýí ÝÊÍÇÊ ãÑåÞ ¡ Ãæ ÞÏ íÍÏÏ ãÚÇáã Úáì ÞíÇÓ ÇáÌÓã (ãËá ÌÒÁ ÇáÍæÇÝ ¡ Ãæ ÍÝÑÉ Ãæ ÇáÊÞÇØÚÇÊ ãæÇÞÚ ÇáÎØæØ æÇáØÇÆÑÇÊ ¡ æãÇ Åáì
Ðáß) æÇáÊí ÇÓÊåÏÝÊ ÈØÑíÞÉ ãÇ. In any case, it is important that the points representing the user-defined coordinate system be targeted precisely or else the accuracy of the transformation will be degraded.
Úáì ÃíÉ ÍÇá ¡ ãä Çáãåã Ãä íãËá äÞØÉ íÍÏÏåÇ ÇáãÓÊÚãá ÊäÓíÞ äÙÇã ÊÓÊåÏÝ Úáì æÌå ÇáÊÍÏíÏ Ãæ ÏÞÉ æÓíÊã ÊÍæíá ÇáãÊÏåæÑÉ. In fact, the accuracy of placing the targets precisely on the user coordinate system's defining features often is the determining factor in overall measurement accuracy.
æÝí ÇáæÇÞÚ ¡ ÝÅä ÏÞÉ æÖÚ ÇáÃåÏÇÝ ÈÏÞÉ Úáì ÇáÊäÓíÞ ÇáãÓÊÎÏã Ýí ÊÍÏíÏ ãáÇãÍ ÇáäÙÇã Ýí ßËíÑ ãä ÇáÃÍíÇä åæ ÇáÚÇãá ÇáÍÇÓã Ýí ãÌãá ÞíÇÓ ÇáÏÞÉ. Fortunately, many different Target Types are available to help with this.
áÍÓä ÇáÍÙ ¡ ÇáåÏÝ ÃäæÇÚ ãÎÊáÝÉ ßËíÑÉ ãÊÇÍÉ ááãÓÇÚÏÉ Ýí Ðáß. See the WINTRANS manual for details on performing coordinate transformations.
ÇäÙÑ WINTRANS ÇáíÏæíÉ ááÍÕæá Úáì ÊÝÇÕíá Íæá ÃÏÇÁ ÊäÓíÞ ÇáÊÍæáÇÊ.
Coordinate systems are also called axis systems since the coordinate system is often defined by aligning certain points to the coordinate axes.
ÊäÓíÞ ÇáäÙã æÏÚÇ ãÍæÑ äÙã ãäÐ ÊäÓíÞ ÇáäÙÇã æÛÇáÈÇ ãÇ íÚÑÝ Úä ØÑíÞ ãæÇÁãÉ ÈÚÖ ÇáäÞÇØ áÊäÓíÞ ãÍÇæÑ. In this document, coordinate system and axis system are used interchangeably and mean the same thing.
Ýí åÐå ÇáæËíÞÉ ¡ æäÙÇã ÊäÓíÞ ãÍæÑ ÇáäÙÇã íÓÊÚãá æÊÚäí ÇáÔíÁ äÝÓå. Measurements
ÇáÞíÇÓÇÊ Types of Measurements
ÃäæÇÚ ÇáãÞÇííÓ Photogrammetry is a versatile, powerful, and flexible measuring technology. Measurements have been done on land, sea (and undersea), and air, and even in outer space on objects smaller than a football to larger than a football field.
ÇáãÓÍ ÇáÊÕæíÑí åæ ÊäæÚÇ ¡ ÞæíÉ ¡ æãÑäÉ ÞíÇÓ ÇáÊßäæáæÌíÇ. ÞíÇÓÇÊ ÃÌÑíÊ Úáì ÇáÈÑ æÇáÈÍÑ (æÊÍÊ) ¡ æÇáåæÇÁ ¡ æÍÊì Ýí ÇáÝÖÇÁ ÇáÎÇÑÌí Úáì ÇáÃÌÓÇã ÇáÊí íÞá áßÑÉ ÇáÞÏã ÃßÈÑ ãä ãáÚÈ áßÑÉ ÇáÞÏã.
Photogrammetry is widely used in the aerospace, antenna, shipbuilding, construction, and automotive industries for a wide variety of measurement tasks.
ÇáãÓÍ ÇáÊÕæíÑí íÓÊÎÏã Úáì äØÇÞ æÇÓÚ Ýí ÇáÝÖÇÁ ¡ æÇáåæÇÆí ¡ æÈäÇÁ ÇáÓÝä ¡ æÇáÈäÇÁ ¡ æÕäÇÚÉ ÇáÓíÇÑÇÊ áãÌãæÚÉ æÇÓÚÉ ãä ÞíÇÓ ÇáãåÇã. Although every photogrammetric project is somewhat different, we have separated them into broad categories to help describe general approaches for performing a successful measurement.
Úáì ÇáÑÛã ãä ßá ãÔÑæÚ ÇáãÓÍ ÇáÊÕæíÑí ãÎÊáÝÉ äæÚÇ ãÇ ¡ ÚáíäÇ Ãä ÊÝÕá ÈíäåãÇ Ýí ÝÆÇÊ ÚÑíÖÉ ááãÓÇÚÏÉ Ýí æÕÝ äåÌ ÚÇãÉ áÞíÇÓ ÃÏÇÁ äÇÌÍÇ. Measurements can be classified as initial or repeat, and as completely overlapping or partially overlapping.
ÇáÞíÇÓÇÊ ÇáÊí íãßä ÊÕäíÝåÇ ÊÍÊ ÇáÃæáíÉ Ãæ ÊßÑÇÑ ¡ æãÊÏÇÎáÉ ÊãÇãÇ Ãæ ÌÒÆíÇ ÇáÊÏÇÎá. The two categories are not mutually exclusive; initial measurements can be completely overlapping or partially overlapping, and so can repeat measurements.
ÝÆÊí áÇ íÓÊÈÚÏ ÈÚÖåÇ ÈÚÖÇ º ÇáÞíÇÓÇÊ ÇáÃæáíÉ íãßä Ãä Êßæä ãÊÏÇÎáÉ ÊãÇãÇ Ãæ ÌÒÆíÇ ãÊÏÇÎáÉ ¡
æåßÐÇ íãßä ÊßÑÇÑ ÇáÞíÇÓÇÊ. In general, a completely overlapping, repeat measurement is the easiest type of measurement while an initial, partially overlapping measurement is the most difficult.
ÈÔßá ÚÇã ¡ ÊãÇãÇ ãÊÏÇÎáÉ ¡ æÊßÑÇÑ ÇáÞíÇÓ åæ ÃÓåá äæÚ ãä ÇáÞíÇÓ ÈíäãÇ ÃæáíÉ ¡ ÌÒÆíÇ ÞíÇÓ ÇáÊÏÇÎá åæ ÇáÃßËÑ ÕÚæÈÉ. Initial and Repeat Measurements
æßÑÑ Ãæáí ÇáãÞÇííÓ A repeat measurement is one in which approximate coordinates are available for all (or nearly all) of the target points, while for an initial measurement there are no approximate coordinates available.
æËãÉ ÊßÑÇÑ ÇáÞíÇÓ ÇáÐí åæ æÇÍÏ ÊÞÑíÈÇ ÊäÓÞ ãÊÇÍÉ ááÌãíÚ (Ãæ ÊÞÑíÈÇ ßá) ãä ÇáãÓÊåÏÝ äÞØÉ ¡ Ýí
Ííä áÝÊÑÉ ÃæáíÉ áÞíÇÓ æÌæÏ Ãí ÊäÓíÞ ÇáÊÞÑíÈíÉ ÇáãÊÇÍÉ. In general, these coordinates are available from an earlier measurement of the object (hence the name repeat measurement), but they can also be from a set of design coordinates. All that matters is that they are accurate enough to allow the software to correctly measure all the targets on each photograph.
ÈÔßá ÚÇã ¡ æÊÊæÝÑ åÐå ÇáÅÍÏÇËíÇÊ Ýí æÞÊ ÓÇÈÞ ãä ÞíÇÓ ÇáÌÓã (ÇáÇÓã ¡
æãä Ëã ÊßÑÇÑ ÇáÞíÇÓ) ¡ æáßäåÇ íãßä ÃíÖÇ Ãä Êßæä ãä ãÌãæÚÉ ãä ÊÕãíã æÊäÓíÞ ßá ãÇ íåã åæ Ãä Êßæä ÏÞíÞÉ ÈãÇ íßÝí ááÓãÇÍ ááÈÑÇãÌ áÞíÇÓ ÕÍíÍ ÌãíÚ ÇáÇåÏÇÝ Ýí ßá ÕæÑÉ. Then, after each photograph is oriented (using the AutoStart or SuperStart procedure), we can use a process called driveback to quickly and automatically find and measure all the visible points.
Ëã ¡ ÈÚÏ ßá ãæÌå ÇáÕæÑÉ (ÈÇÓÊÎÏÇã ÅÌÑÇÁÇÊ ÊÔÛíá ÊáÞÇÆí Ãæ SuperStart) ¡ íãßääÇ
ÇÓÊÎÏÇã ÚãáíÉ ÊÓãì driveback ÊáÞÇÆíÇ æÈÓÑÚÉ áÇíÌÇÏ æÞíÇÓ ßá äÞØÉ ãÑÆíÉ. To use driveback, the coordinates should be much more accurate than the closest target spacing.
ÇÓÊÎÏÇã driveback ¡ íäÈÛí Ãä ÊäÓÞ ÃßËÑ ÏÞÉ ãä ÃÞÑÈ åÏÝ ÇáãÈÇÚÏÉ. Therefore, if targets are 100mm (4 inches) apart, the coordinates' accuracy should be much better than this, say better than 25 mm (1 inch).
æáÐáß ¡ ÅÐÇ ÇáÃåÏÇÝ 100mm (4 ÈæÕÇÊ) ãÇ ÚÏÇ Ðáß
¡ íäÓÞ 'ÇáÏÞÉ æíäÈÛí Ãä íßæä ÃÝÖá ÈßËíÑ ãä åÐÇ ¡ æíÞæá ÃßËÑ ãä 25 ãã (1 ÈæÕÉ). The better the approximations are, the faster and easier the measurement will be.
ÃÝÖá åí ÊÞÑíÈíÉ ¡ æÃÓÑÚ æÃÓåá æÓíÊã ÞíÇÓ. If no approximate coordinates are available, you can use the AutoBar provided with the system to do an initial measurement.
ÅÐÇ áã ÊäÓÞ ÇáÊÞÑíÈíÉ ÇáãÊÇÍÉ ¡ íãßäß
ÇÓÊÎÏÇã AutoBar ÊÒæíÏ äÙÇã áÞíÇÓ ÃæáíÉ. With the AutoMeasure command, initial measurements are now nearly as fast and easy as repeat measurements.
ãÚ AutoMeasure ÇáÞíÇÏÉ ÇáÞíÇÓÇÊ ÇáÃæáíÉ ÇáÂä äÍæ ÃÓÑÚ æÃÓåá ãÇ ÊßÑÑ ÇáÞíÇÓÇÊ. Completely or Partially Overlapping Measurements
ßáíÇ Ãæ ÌÒÆíÇ ÊÏÇÎá ÇáãÞÇííÓ A completely overlapping measurement is one in which the entire object is seen in every photograph, while in a partially overlapping measurement, the object must be photographed in sections (because of space limitations or accuracy requirements or because of the complexity of the object). Partially overlapping measurements must have sufficient common coverage to hold (or "tie") the entire measurement together as a unified whole.
æËãÉ ÊÏÇÎá ÊãÇãÇ ÞíÇÓ æÇÍÏ Ýí ßÇãá ÇáÌÓã æíäÙÑ Ýí ßá ÕæÑÉ ¡ ÌÒÆíÇ ¡
Ýí Ííä Ãä ÞíÇÓ ÇáÊÏÇÎá ¡ æÇáÌÓã áÇ ÈÏ ãä ÊÕæíÑå Ýí ÇáÝÑæÚ (ÈÓÈÈ ÖíÞ ÇáãßÇä Ãæ ãÊØáÈÇÊ ÇáÏÞÉ Ãæ ÈÓÈÈ ÊÚÞíÏ ãæÖæÚ). ÌÒÆíÇ ÞíÇÓÇÊ ÇáÊÏÇÎá ÚÇã íÌÈ Ãä íßæä ßÇÝíÇ áÊÛØíÉ ÚÞÏ (Ãæ "ÇáÊÚÇÏá") ßÇãá ÞíÇÓ ãÚÇ ßßá ãæÍÏ. The need for common coverage among photographs is described with the help of the figures below.
ÇáÍÇÌÉ Åáì ÊÛØíÉ ÚÇã Èíä ÕæÑ æíÑÏ ÈÝÖá ÇáÃÑÞÇã ÃÏäÇå.
In the first figure, we have two completely independent measurements of two flat panels.
Ýí ÇáÑÞã ÇáÇæá ¡ áÏíäÇ ÏæáÊíä ãÓÊÞáÊíä ÊãÇãÇ ÞíÇÓÇÊ ÇËäíä æÍÇÊ ãÓØÍÉ. Each of the panels is very accurately measured, but since there is no common coverage, we can say nothing about the relationship between the two panels.
ßá ÝÑíÞ ãä ÇáÝÑíÞíä åæ ÞíÇÓ ÏÞíÞ ááÛÇíÉ ¡ æáßä äÙÑÇ áÚÏã æÌæÏ ÊÛØíÉ ÚÇã ¡ íãßääÇ
Ãä äÞæá ÔíÆÇ Úä ÇáÚáÇÞÉ Èíä ÝÑíÞíä.
For example, we cannot even say how far the panels are from each other or how they are oriented to each other.
Úáì ÓÈíá ÇáãËÇá ¡ áÇ íãßääÇ ÍÊì ÇáÞæá ãÏì ÇáÃÝÑÞÉ Úä ÈÚÖåÇ ÇáÈÚÖ ¡
æßíÝ ÃäåÇ ãæÌåÉ äÍæ ßá ãäåãÇ ááÂÎÑ.
If we now measure the panels with enough partial overlap that a line of points is seen in common between the two panels, we have now connected the two panels together but not with sufficient overlap to completely determine the relationship between the two panels.
ÅÐÇ ßäÇ ÇáÂä ãÚ ÝÑíÞí ÞíÇÓ ÇáÊÏÇÎá ÇáÌÒÆí íßÝí Ãä ÇáÎØ åæ äÞØÉ Ýí ÚÇã Èíä ÝÑíÞíä ¡ áÏíäÇ ÇáÂä ãÑÊÈØÉ ÇáÝÑíÞÇä ãÚÇ æáßä áíÓ ÈãÇ íßÝí ÊãÇãÇ áÊÏÇÎá ÊÍÏíÏ ÇáÚáÇÞÉ Èíä åÐíä ÇáÝÑíÞíä.
The common line only acts like a hinge, the two panels are connected there but they could be at any angle to each other that this "hinge" connection allows.
ÎØ ÇáãÔÊÑß ÅáÇ ÇáÃÝÚÇá æßÃäåÇ ÊÊæÞÝ ¡ ÝÑíÞÇä ÊÑÊÈØ åäÇß æáßäåÇ íãßä Ãä Êßæä Ýí Ãí ÒÇæíÉ ãä ÈÚÖåÇ ÇáÈÚÖ Çáì Çä åÐå "íÊæÞÝ" íÓãÍ ÇáÕÏÏ. Therefore, the overlap must be more than just a line of points; it must be at least two-dimensional.
æáÐáß ¡ ÝÅä ÇáÊÏÇÎá íÌÈ Ãä Êßæä ÃßËÑ ãä ãÌÑÏ ÎØ ãä ÇáäÞÇØ ¡ Èá
íÌÈ Çä Êßæä Úáì ÇáÇÞá ËäÇÆíÉ ÇáÃÈÚÇÏ. If we now add a third point in common between the two measurements that is away from the line (so the three points form a triangle), the "hinge" is now locked in place and the relationship between the two panels is established.
ÅÐÇ ßÇä áäÇ Ãä äÖíÝ ÇáÂä ÇáäÞØÉ ÇáËÇáËÉ Ýí ÚÇã ÇáÞíÇÓÇÊ Èíä ÇáÈáÏíä ÈÚíÏÇ Úä åÐÇ ÇáÎØ (ÍÊì ËáÇË äÞÇØ Úáì Ôßá ãËáË) ¡ "íÊæÞÝ" åæ ÇáÂä Ýí ãßÇä ãÛáÞ ¡
æÇáÚáÇÞÉ Èíä ÝÑíÞíä åæ. Therefore, as a minimum, there must be three points, forming a triangle that is seen in common between the two sets of photography.
æáÐáß ¡ ßÍÏ
ÃÏäì ¡ íÌÈ Ãä íßæä åäÇß ËáÇË äÞÇØ ¡ æÊÔßíá ãËáË Ãä íäÙÑ Ýí ÚÇã Èíä ãÌãæÚÊí ÇáÊÕæíÑ. Of course, by adding more points and more overlap the tie between the two panels is more strongly established.
æÈØÈíÚÉ ÇáÍÇá
¡ Úä ØÑíÞ ÅÖÇÝÉ ÇáãÒíÏ æÇáãÒíÏ ãä äÞÇØ ÇáÊÏÇÎá ÇáÊÚÇÏá Èíä ÝÑíÞíä ÃßËÑ ÈÔÏÉ. The strongest tie between the two panels is
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