On return the variable parameters X and Y contain the position (in pixels) of the top left corner of the image. This position information can be used to stitch several images to a larger mosaic, where [X,Y] defines the position of the tile in the mosaic coordinate system. If the tile position is undefined both X and Y are set to -1.
The following figure shows the positions of several tiles. The coordinates returned by GetTilePos are indicated by red dots.