I am looking to tile large image documents don't necessarily have anything to do with the world coordinate system. For example, I have zoom level 1 at (768 x 768 pixels) or 3x3 tiles at 256by256px. Zoom level 2 at 1536 x 1536 pixels (or 6x6 tiles). However, the geographic coordinates cut off outer right and lower tiles (probably because of the way that the geographic coordinate system works).
Basically, I'd like to set the origin at (0,0) and then tile accordingly to (width, height) in pixels of the corresponding zoom level.