User Manual - pancroma

There are a few rules of thumb regarding selection of such points. They shouldbe clear, precise and preferably man-made. (Some natural features are clearand precise. However there is a possibility that they may shift position over time.Features such as river bends, edges of snow fields and the like may migrate overtime and yield errors. Features such as crossroads, buildings and bridges aregenerally more reliable.)IMPORTANT NOTE: Make sure that your points are NOT co-linear. This willlead to a singular matrix and a bad result. The points should be spaced as far aspossible apart as possible (for example two upper corners and the middle of thebottom edge) and preferably close to the edges of the image.Some control points that I used for an example registration are shown below.The first image shows a distinct crossroads. (The corner of the white lot or asmall building could have been used as well.) The second image shows somesmall islands that could serve as suitable control points. The third image showsthe intersection of a road and a dry wash. Although using the wash could bedangerous, inspection of the two images showed the signatures to be exactlyequal so I suspected that the location had not moved between the images.176