We have developed the extraction software in C on a Unix and X windows platform, as part of a system which provides a wide variety of tools for curvilinear feature extraction. When applying the minimum cost path algorithm, the user defines the search area and selects the start and end points with a mouse. The relative weighting between the terms that are used to calculate the cost may be adjusted and the resulting minimum cost path is shown highlighted and superimposed on the original image as shown in figure 5.
An alternative tracking tool has also been implemented in which the user may provide rough digitising points along the path of the curvilinear feature. The software tracks the rough points by applying a search window around adjacent pairs of specified points and performing a global search within the moving window using the extended d'Esopo algorithm. In order to allow for the roughness of the digitising the start point in all but the first window is chosen a few points back along the minimum path found in the previous window. This allows the user to be less accurate without affecting the integrity of the final path.