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Usage and Optimization Notes

Multiple images on a single map

You may have to transform or mosaic a number of images on a map to display the whole of a large site.  In this case, the images will usually overlap.

The programme adds colour to an image using the following rules:

The map is examined line by line of pixels from the top down. For each line starting at the left, the programme looks to see if a pixel is black, white or an intermeidate gray or colour value. If it's black, corresponding to a map feature, it is either left alone or converted to white depending on the line choice in Options.  If it's white, it's filled with the spectral colour corresponding to the interpolated height at that point on the map.  If it is an intermediate value, data has been reached and the scan from the left stops. The process is then repeated scanning from the right side of the image.  In this way the white areas of the map are coloured up to the boundaries of the transformed data.

In the case shown above, however some parts of the overlapping areas will not be coloured, because they are occluded by image data  encountered during the scan and the area beyond it remains uncoloured.

This problem can be overcome by rotating the map with the images in AirPhoto so that the scan from left to right and from right to left enters all areas without encountering image data.  You cant not use an image processing programme to perform the rotation, because the height data must also be rotated to precisely the same extent as the image data. The result of doing this in AirPhoto and then repeating the run with the programme is then: