% Estimate lengths on an image by point-click.
% [lengths] = image_measure;
% This function prompts the user to select an image file to open, then
% opens and plots the image. The program waits for the user to resize the
% image if desired. The user then:
% 1.) left-clicks on the endpoints of a known dimension in the image to
% establish a reference length and then
% 2.) types the length of the reference in a dialog box,
% 3.) clicks on as many pairs of points as desired in the image to measure
% their separation distance relative to the reference.