These function are used to create "contour" lines around the TAG values on the 2D frames.
A contour is composed of a series of points on the frames and a series of "connectivity" informations that tell how the points are linked to create the contours loops.
The following functions are used to create, update and delete the contours.
The following functions are used to get access to the contour information.
The following functions are used to draw the contours.