BGLcomp SDK textureIndex... What?

Hi,I have been adding some buildings to home airpark and have all the textures in the SDK printed as pictures (maps) with their reference numbers. I get to the textures OK but having a time with textureIndex (s). I thought they specified the end of the map. Most are 128x128. For example I thought 127,127 would be the SE corner of the map. However the SDK examples go way out of the 128x128 range but they don't blow up. I have some luck moving the x,z to some point within the maps but also with 0,0 255,255, etc. How about the y reference used in the window texture maps (xyz there but not in roof, top, etc.)? I anyone out there can explain how these textureIndex (s) really mean I would appreciate it. I don't need code examples, just the meaning other than provided in the SDK. I assume that more than one of you has been playing with these and found out more than I have to now.Help,Larry Costa