CAPA Camera constant and principal-point position
Columns | format | contents/explanation | |
|---|---|---|---|
1-4 | A4 | CAPA | |
5-7 | I3 | Code which indicates the values to be introduced as unknowns blank :none 1 :camera constant c' 2 :principal point PPA xH', yH' 3 :all three values c', xH', yH' | |
8-23 | A16 | Camera name | |
24-33 | F10.0 | Camera constant c' | |
34-43 | F10.0 | xH' principal-point position (principal point of auto collimation PPA | |
54-62 | F9.0 | sc' | corresponding empirical standard deviations |
81-83 | I3 | Groups of cameras with special standard deviations of their photo measurements. Use an empty field for the common group. Three special groups are possible. (Digits 1 to 3) | |
This input statement is necessary for each camera in use, and must contain at least the camera name and the camera constant.
The photo coordinates shall be related to the principal point of symmetry PPS. If the principal point of auto collimation PPA differs from PPS, it has to be indicated here.
A code in columns 5-7 means that for this camera either camera constant or principal-point position or both are carried in the adjustment as unknowns. If there is no such code, then camera constant and principal point are treated as fixed values, which is reasonable for those cases where an object has been photographed only from above and has no depth. For all other cases, it is recommended to set the code to 3 and to give appropriate values for the standard deviations in columns 54-80. Thus camera constant and principal point are introduced to the adjustment as observed unknowns.
There are no default values for the standard deviations. Values from any preceding CAPA statement will not be transferred to a next one. Values of 0.005 mm to 0.050 mm are recommended for the standard deviations, depending on the accuracy of the predefined camera data. When using amateur cameras larger standard deviations must be assumed.
If a focusable camera is used, then for each principal distance used a separate camera must be defined.
For cameras providing a different standard deviation for the image measurements, groups of cameras can be created. In the subsequent GRUP statement a factor can be defined.
Attention:
When no a priori standard deviation is defined for an unknown camera parameter, no observation equation will be established for this observation. An appropriate warning is displayed. Those unknowns are treated as free unknowns.
A standard deviation will be ignored, if no code is defined in column 6.