Understanding texture coordinates

Hello,

please have a look at the following files:

  • toto.skp contains just a textured rectangle in a XZ plane.

  • model.jpg shows what toto.skp looks like in SketchUp. I name the 4 extremity points of the rectangle “0”, “x”, “z” and “xz”.

  • texture.jpg is the image used to texture the front face of the rectangle. I reported the 4 extremity points of the rectangle in this image.

  • params.xlsx and params.jpg show the different coordinates of the 4 rectangle vertices and the parameters given by SUTextureGetDimensions.
    The x,z (and y) coordinates are given by SUVertexGetPosition.
    The u,v,q ones are given by SUUVHelperGetFrontUVQ.
    The s,t ones are the coordinates in the texture image I estimated by watching the rendering in SketchUp.

Please what is the relation between these coordinates and parameters ?

Thank you.

attachment.zip (400.5 KB)