KB10334 - I am working with scans of very old historical maps, with sometimes high distortion levels, covering a large part of the globe. The 1st, 2nd, and 3rd order polynomial rectification calculations do not seem eliminate enough of the distortion from these maps. Do you have any ideas?

When the multi-segment polynomial approximation method of rectification is introduced in a post 2.0 version of the AIC, this method will help greatly in such situations because it supports the use of a greater number of GCP points in the rectification calculation. The multi-segment method can use an unlimited number of GCPs in the rectification calculation.

Until support for the multi-segment method is added to the AIC, you can simulate the effect of the multi-segment method by loading a source map file into the Project Manager project list multiple times - perhaps four, six, or eight times – resulting in multiple incidences of the same map image in the project list. Then use the bounding polygon tool in the AIC Editor module to to reduce the active portion of each incidence of the file to an area that is only slightly larger than 1/4, 1/6, or 1/8 of the overall image. The active portions of each incidence of the map image should, when added together, cover the entire map coverage. The active areas should overlap by a small degree ensure that there are no gaps between the active areas. Then use the 3rd order polynomial approximation method to rectify each portion of the original map file and generate an output mosaic from the individual active portions. The result of using 10 GCPs to rectify each 1/4, 1/6, or 1/8 of the original map image is that a total of 4 x 10 = 40, or 6 x 10 = 60, or 8 x 10 = 80 GCPs are used to perform the rectification transformation. This results in a more intensively rectified output than if the source map image were simply rectified as a whole.