How to calculate the number of observation values in the adjustment of beam method regional network in photogrammetry? How to calculate the necessary observation number?

The unknowns are the x, y, z of unknown horizontal height and the x, y (all geodetic coordinates) coordinates of elevation points, as well as the six external orientation elements of each photo.

The observed value is the X and Y measured value of each leveling control point, elevation control point and unknown leveling point in all the photos that have appeared (even in several photos).

The number of necessary observations is the minimum number of observations needed to solve equations, which is actually the number of unknowns, because each point can list two * * * line relationships, one X and one Y, but this concept is not commonly used in regional grid beam method leveling.