On Nov 9, 2007 9:21 AM, Frederic Bouvier <> wrote:
> > Is there still any work on FGSD? I think it could be a
> > wonderful alternative to terragear, platform
> > independant and userfriendly when removing the bugs...
>
> I definitively need help for that. FGSD falls on numerical errors in the
> underlying geometry.
>
This problem continually plagues the terragear project as well. When you
combine real world data (i.e. any and every worst case situation possible)
with the limits of numerical accuracy, all kinds of problems can develop.
The terragear project has code sprinkled all over that tests for all kinds
of degeneracy and problems that emerge.
For instance, the polygon clipping library can produce edges that form zero
area peninsulas (double back on themselves.) Extremely thin slices can
emerge. You end up with triangles so small that numerically their area
evaluates to zero. It's possible that features and edges are created that
will crash or hang the delauney triangulator. There's always a possibility
of a real bug, but 99.9% of the the time when I investigate these issues
down to the deepest level, it turns out to be some sort of
numerical/floating point degeneracy that leads to some nonsensical
structure, and the actual algorithms are solild and robust and trying to do
their best.
For what it's worth, terragear has earned the nickname "terror gear", but
seriously, this stuff is 10x harder than any other code I've been involved
with. It's very difficult stuff. I'm sure I've put at least as much
personal effort into the terragear tools over the last 10 years as I have
into the rest of FlightGear combined. That's not to say they are perfect or
don't have plenty of limitations. And I have a set of patches I still need
to look at incorporating. TerraGear has served a purpose, and maybe it's
meant to go on for years to come, but if someone came along and gave us a
next-gen scenery engine, I'd love it!
Regards,
Curt.
--
Curtis Olson: http://baron.flightgear.org/~curt/
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