Control points are 3d points with known values and they can be expensive or difficult to obtain, so often we try to minimize how many are used. This section describes the scenarios and background for use of a minimal number of control points.
The minimum number of control points for successful processing depends on how the control points are marked / assigned, and a Preference setting. Below is a short summary of the requirements, and then sections on common scenarios of control setup and additional background information are presented.
Control Setup Summary
If Control Points have been assigned to objects (points or camera stations), certain minimums must be met for processing to continue:
• There must be at least 4 control assignments total in the project (to points, camera stations or a mixture).
• If any control are assigned to points on photos then:
• Every active photo in the project should have 4 or more control points marked, or
• No active photo in the project has 4 or more control points marked, and there are 4 or more control points, anywhere in project, marked on 2 or more active photographs each, or
• There is at least 1 active photo with 4 or more control points marked (P4), there are 4 or more control points, anywhere in project, marked on 2 or more active photos each, and all other active photos share enough points with P4 to orient (or share points with an active photo that shares points with P4 recursively).
• In addition, if Inverse Camera is being solved, the minimums above might be higher than 4, depending on the number of parameters being solved. Note, an ‘active’ photo is one not set to ‘do not use’, and that is oriented (or can be oriented).