I'm posting here to the general devel list in hopes that someone here can help me with a nurbs problem.

First a little background. FlightGear has non-flat airport surfaces. Unfortunately DEM data is *way* too noisy and has too much potential for odd artifacts to use directly. What I have done is to take a coarse grid of points over the surface of an airport ... sample the raw dem data and come up with an average elevation for each grid point. Then I fit a nurbs surface through this coarse grid and drapped the airport over the nurbs surface. The nurbs surface gives "natural" elevation changes, covers the entire area smoothly, and allows me to filter out all the DEM noise and artifacts.

I have been using nurbs++ (libnurbs.sf.net) as my nurbs library to do this. However, the 3d support of nurbs++ seems to be problematic and buggy. I can't reach the author for help, and the 3d portions of the lib are absolutely not documented.

I find that when I try to interpolate a nurbs surface through the grid points, the resulting surface misses many/most of the points, which is not what I expected. I also tried a least squares fit which actually I *really* like, however, I'm finding that the least squares fit blows up on some data sets for no apparent reason ... there's nothing ill defined about the data sets it is blowing up on.

This is a major headache for me since I'd like to rebuild all the airports and the world scenery *NOW*.

Does anyone have any experience with nurbs++ or any other nurbs library who could help me out here? I'm *not* looking for people who can help me google. I'm looking for people with actual experience and who know something about nurbs who can either help me debug the problem with nurbs++, or who can suggest an alternate and more robust library. I don't need an all encompassing nurbs library, I just need something that can fit a nurbs surface to a set of data points.

Thanks in advance, I'd really like to get the next world rebuild moving again here.


Curtis Olson        http://www.flightgear.org/~curt
HumanFIRST Program  http://www.humanfirst.umn.edu/
FlightGear Project  http://www.flightgear.org
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