Metrology - The Second Part of Photogrammetry for better concept of photogrammetric camera

Metrology is the Second Part of Photogrammetry Photography in its broadest sense is a process that converts the real 3-dimensional world into flat 2-dimensional images. The photogrammetric camera is the device that makes this transformation or mapping from 3 dimensions to 2 dimensions. Unfortunately, we cannot map the 3-dimensional world onto two dimensions completely so some information is lost (primarily the depth).
Photogrammetry in its broadest sense reverses the photogrammetric camera process described above. It converts or maps the flat 2-dimensional images back into the real 3-dimensional world. However, since information is lost in the photogrammetric process, we cannot reconstruct the 3-dimensional world completely with just one photograph. As a minimum, we require two different photographs to reconstruct the 3-dimensional world. If this process was perfect, the two photographs are more than enough information to perfectly reconstruct the 3-dimensional world they represent. Unfortunately, the photogrammetry photography and measuring process is not perfect so the reconstruction of the 3-dimensional world is also imperfect.

However, we can take more photographs and use the extra information in them to improve the photogrammetric process. The 3-dimensional coordinates we Produce from the measurements of multiple photographs are the end result of photogrammetry.
Photogrammetry uses the basic principle of Aerial Triangulation, whereby intersecting lines in space are used to compute the location of a point in all three dimensions. However, in order to triangulate a set of points one must also know the photogrammetric camera position and aiming angles (together called the orientation) for all the pictures in the set. A process called Resection does this. Finally, because the V-STARS photogrammetric camera is a precision measuring instrument, it must be calibrated so its errors can be defined and removed. 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.

Although each of these photogrammetry techniques is best described separately, they are actually all performed simultaneously in a photogrammetric process called the Bundle Adjustment.