Posthole

Posthole is a program for detecting rectangular structures in scanned excavation plans, digitizer output, or in imported co-ordinate lists of holes and other features. You can use the normal Mark, the Enlarge+Mark, or the Zoom + Mark menu options to mark individual postholes. Move the mouse cursor to hole and when the cross-hair is over the centre of the hole, left click.

You must mark at least one hole and expand or contract the little circle so that it is completely surrounded by some white space. You may have to experiment with the amount of white space used to get the best results by selecting and running the option again.

When you finish selecting holes, press either Alt-O or click again on the Holes menu item. Then, the AutoMark menu option will be activated, and you can click on it to start computation.