The science of making measurements from aerial photography. Determine non-distorted coordinates, horizontal ground distance and angles from measurements on a single vertical photo. Determination of object height from relief displacement. Determine heights from image parallax measurements. Use the PP as the origin.
X axis is taken to be the fiducial axis.
Y axis is 90 counterclockwise from the X. Coordinates have positive and negative values. Points are shifted radially to or from nadir depending on their elevation. So angles and distances are distorted on aerial photos taken in areas of great relief. Measure the photo coordinates. Convert photocoordinates to datum-level ground coordinates.