Control Points

When running AT using control points there are 2 options. The manual says:

  • Use control points for adjustment (need a valid control point set): The block is accurately adjusted to control points (advised when control points accuracy is consistent with the resolution of input photos).
  • Use control points for rigid registration (need a valid control point set): The block is rigidly registered to control points without handling long range geometric distortion (advised for inaccurate control points).

What is the difference between accurately adjusted and  rigidly registered and when would you use one or the other? 

Parents
  • Use control points for adjustment - This is used with accurate survey control, when used it weights the positions of the photos where the control is marked positioning them exactly at this control location.

    Use control points for rigid registration - This is used when the control is not survey accurate, i.e. if control coordinates are extracted from lower resolution scene to position (spatially reference) imagery captured from the ground. When used the photos exterior orientation is first computed then the block is positioned over the control using a network least square adjustment distributing the error across all the controls

    Michael Barkasi

    Application Engineer 

    Reality Modeling



Reply
  • Use control points for adjustment - This is used with accurate survey control, when used it weights the positions of the photos where the control is marked positioning them exactly at this control location.

    Use control points for rigid registration - This is used when the control is not survey accurate, i.e. if control coordinates are extracted from lower resolution scene to position (spatially reference) imagery captured from the ground. When used the photos exterior orientation is first computed then the block is positioned over the control using a network least square adjustment distributing the error across all the controls

    Michael Barkasi

    Application Engineer 

    Reality Modeling



Children
  • That was my initial thoughts as I have worked with other photogrammetric software which have similar approaches.  However I recently ran AT independently on two sets of photos (no control) and the relative orientation results were acceptable;  when I combined the photos into one block the results were very poor.  I used Google to get a few control points ( in-accurate) and added them to the two sets of photos.  I reran AT using  the 'control points for adjustment' and the 'rigid registration' options and the results were completely different.  The 'control points for adjustment' (accurate) worked but the 'rigid registration (in-accurate) was very bad. I thought it would be the reverse seeing as how the control was in-accurate, hence my question.  I have always used control points from ground survey in previous projects so I have never used the 'rigid registration' option.  I will do some additional tests

    Farouk Rohoman