Register Image Caveats
Affine image registration directions.
||Full TM scene. The swath width is about 185 km, and the orbit
is broken in scenes that are approximately square.
arrow shows the satellite's path, which is a "polar" orbit with small
The UTM map projection keeps the scene geometry, but it is rotated
and there are triangular voids on all sides.
||If you had the original imagery, with respect to the satellite, the
scenes would be square, but would not line up with the UTM grid.
Airplanes could fly in any direction, so that in general you cannot
expect north to be at the top of the image, except in a very general
sense. The same applies to a map that you would scan; unless you
were very lucky, scanning would introduce an angular rotation because
you would most likely not be able to place the map in the scanner
Caveats on image registration, which might work if the simple
World file options will not:
- The MICRODEM image registration provides a "quick
and dirty" result. It should only be used
carefully, and as a last resort.
- If your image has geometric distortions, or relief displacement, the simple
affine transformation used cannot work well.
- This should only be used for a large scale imagery of a
- If your image has an inappropriate projection, the simple
affine transformation used cannot work well. The
smaller the scale of the image (the larger the area
covered), the greater the chance that this will not work.
- If you scan an image, you almost certainly have to use
this method (or rotate the image), because other
alternatives (like world files)
assume that the map's grid is oriented north-south and it
is impossible to get that in a scan.
- The following will limit the effectiveness of this
- Camera lens distortion (poor optics).
- Off-nadir viewing geometry.
- Terrain displacement in steep areas.
- Scanner imperfections and distortions.
- If at all possible, let a professional handle this.
In addition to errors that you might make, your data may
not be possible to register using this simple technique.
World file and grid types.
Delaunay triangulation registration
is valid in a wider range of cases.
Last revision 12/3/2017