Although the photogrammetry equipment the photogrammetric cameras and lenses used in the photogrammetry V-STARS system are of the highest quality, they must still be precisely calibrated to remove errors that are present in the system. Some of these calibration error terms of this photogrammetry equipment can be described in terms of their physical cause while others are more empirically derived. 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 photogrammetry orientation (position and aiming angles) of each picture in a process called the Bundle Adjustment.
This ability to calibrate the photogrammetry equipment the photogrammetric camera as a byproduct of the measurement is called Self-calibration and it means the camera used for photogrammetry will be calibrated at the time of measurement, and under the environmental conditions that exist (temperature, humidity, etc.) at the time of measurement. This is far superior to relying on an old and possibly outdated laboratory calibration that may have been done under dramatically different conditions than existed at the time of measurement.
There are certain requirements that must be met in order to self-calibrate the photogrammetry equipment the photogrammetric camera, but they are usually easy to do. 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.
Although you will get better photogrammetry results if you take about half of your shots one way and half the other, this is not critical. What is critical is that you must have at least one picture that is rolled approximately 90° differently than the others. If you do not, you cannot self-calibrate the photogrammetry equipment the photogrammetric camera. Instead, you will have to rely on a pre-existing calibration that is less reliable and less accurate.
A second requirement for using self-calibrate the main photogrammetry equipment the photogrammetric camera is that you must measure a minimum number of photographs taken from a minimum number of different locations. 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 threedimensional.
Also, the photographs should be taken from at least three different locations. Since most jobs will take at least this many photographs there is usually no reason not to self-calibrate the photogrammetry equipment the photogrammetric camera. 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. A final photogrammetric requirement is that you must have a minimum number of welldistributed points on each photograph and for the entire measurement.
Specifically, you should have at least twelve well-distributed points on each photograph, and at least twenty points for the entire measurement. Well-distributed means the points are distributed fairly evenly throughout the photograph captured by photogrammetry equipment camera. 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.
Posts
