You will not be surprised to learn that my problems with Map resulted from an oversight. Because I wasn't careful with my coordinates, I was actually mapping elevations from an area outside my data region (which doesn't fill the rectangle), therefore the 0 values were correct. Sorry to waste bandwidth.
But wait, there's more! I am now rendering my image with the TIFF painted on the rubbersheeted surface. To recap, I first create a grid with the same connectivity as the TIFF, but with positions in the frame of reference of the elevation data. I then Replace the colors in this field with the TIFF colors. At this stage I have a nice looking image. Meanwhile I have Imported the elevation data (which when Rubbersheeted produces a nice surface). I then use Map to put elevations into the object with the TIFF colors. If I render at this point it still looks fine. The final step is to Rubbersheet the field. The image produced does not look nice. The elevations are correct, and the colors are roughly right, but there is an ugly graininess. Zooming in shows that something bad has happened, an odd effect that is hard to describe but looks a lot like a bug. I have found that the image is cleaned up if I Collect it with an AmbientLight. Since AmbientLight removes the default lighting, which is ambient [0.2 0.2 0.2] plus a distant light, I'm guessing that the problem is related to what happens to the image lighting/colors when Rubbersheet is applied. Anyway, I now have something useable, and have learned a lot through all this. Thanks to all who offered help. Gib > NOTICE - This e-mail is only intended to be read by the named recipient. It may contain information which is confidential, proprietary or the subject of legal privilege. If you are not the intended recipient please notify the sender immediately and delete this e-mail. You may not use any information contained in it. Legal privilege is not waived because you have read this e-mail. For further information on the Beca Group of Companies, visit our web page http://www.beca.co.nz
