On Sunday 06 January 2008 21:05, Ralf Gerlich wrote: > Hi again! > > Ralf Gerlich wrote: > > This has to do mostly with the special cases introduced for > > rounding (regarding SG_EPSILON) and for covering the difference > > between (int) cast rounding towards zero and the desired > > behaviour more similar to a floor(). > > The problem only occurs for latitudes north of 83N or south of > 83S western longitudes. Only here the longitudinal span of > buckets is above 1.0 and always divisible by 2, so that the > center of a bucket always lies on an integral longitude. > > This leads to the fabs(diff)<SG_EPSILON condition in > newbucket.cxx:109 to evaluate to true and therefore activates the > wrong calculation. Casting to (int) always rounds towards zero, > which in this case leads to the base longitude being shifted > eastwards by one span. > > In case of latitudes north of 89N or south of 89S non-western > longitudes (>=0) will lead to a base longitude of 0, while > western longitudes will lead to a base longitude of -180. This > means that the single tiles surrounding the polar caps (width 360 > degree, height 1/8 degree) essentially have different tile > numbers depending on whether one is coming from an eastern or a > western latitude. > > This might also explain the "missing northpole"-problem reported > by Torsten Dreyer some time ago. Another possibility would be > that Curt's last build failed in a similar way as ours did and > there are not northpole tiles ;-) > > Cheers, > Ralf
I think I mentioned earlier, but first problem - there's no SRTM data for the poles. Second problem is that calculations that assume a quad (trapezoidal) area fail at the poles because they have to deal with a tri area and not a quad area. LeeE ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
