Automatic Rectification of Images through Scale Independent Targets

In the paper, a procedure for the automatic rectification of images is described. The procedure uses some targets fixed to the vertices of a 2 m x 2 m square frame. The frame is positioned on the surveyed surface (e.g. a building facade or a road where an accident occurred). The position of the target vertices is obtained through a correlation between the image we should rectify, and the image of the target. The design of the targets has been made in order to obtain a scale independent correlation; for this reason, the correlation is influenced by a rotation. The target in the stored image, and in the image to be rectified, has different orientations. For this reason an error in the determination of the vertex position occurs. The rough position values of the targets vertices can be used to obtain transformed target images which allow a fine correlation. The description of the procedure and the results of a test are reported. A different colour coded target has been studied and tested, with good results.