Overview

Pexel control points define how a triangulation is texture mapped by an image.

Pexel control points consist of two components; first a real world coordinate specifying its location on the triangulation and secondly a normalised image coordinate specifying its location on the image, i.e. X and Y values are in the 0-1 range. The lower left hand corner of the image is (0, 0) and the upper right hand corner is (1, 1). Co-ordinates in the image are a fraction of the width and height. For example, if the image was 400 by 300, then the point (200, 100) would be (0.5, 0.3333) in normalised coordinates.

Control points allow all or part of an image to be draped over all or part of a triangulation. At least three control points are required to handle the draping of an image over a triangulation. If no control points are specified, then the image is draped over the entire triangulation. How accurately the image maps onto the triangulation depends upon the number of control points, mapping mode used and how accurately the control points are registered.

For example, consider a triangulation with world coordinates that span from (10, 10, 10) in the lower left to (40, 40, 40) in the upper right and an image with dimensions 1-480 in the X direction and 1-300 in the Y direction. A control point with world location (10, 10, 10) and normalised image location of ( 0, 0), would link the lower left corner of the image to the lower left corner of the triangulation. Similarly, a control point with world location (40, 40, 40) and normalised image location (1, 1) would link the upper right corner of the image to the upper right corner of the triangulation.

The image and its associated control points are stored in a pexel file (<name>.pexel). Images that are a CompuServe GIF or Silicon Graphics Industry (SGI) RGB file can be converted to.pexel files through the options under the File > Convert submenu. If the source image is not a CompuServe GIF or SGI RGB file, then there are many third-party and shareware programs available that can convert the image to one of these formats.

Pexel control files, which are binary files, can be exported to an ASCII file through running the script pcrdump