Hello again! It seems that I finally have a somewhat dependable workaround for the TerraGear coastline bug reported shortly after the release of the 1.0.0 scenery.
I have reviewed the algorithm thoroughly - together with Martin - and checked some of the tiles reported as faulty beginning of this year and they seem to be generated correctly now. Martin and I plan to start a new generation job on the weekend of the 16th/17th of August. We would like to include the current state of the static scenery database with this release. In case anybody has any objects intended for submission but not yet submitted, this is the time to submit them to the database, if you want to have your contributions included in the new scenery. As this scenery is to replace the faulty scenery which was released together with FlightGear v1.0.0, we will have to use the airport database included with that release for consistency reasons. Updates as found in the apt.dat in CVS will therefore unfortunately not be included. (As a sidenote: This is one reason why the apt.dat or at least the parts thereof used for airport generation as well as the AI ground networks should reside with the scenery, not with the base package...) We intend to tag the generated scenery "unstable" for obvious reasons before making it an official release. While it seems to me that the workaround should work, due to previous experience with TerraGear and its subtleties I would not want to bet on it. As it seems, some mirror providers may not be able to carry the load of two scenery releases - the official one and the unstable version -, so we will not publish the alpha release via the normal distribution channels, where mirrors normally pick it up. Possibly, we will publish a location were interested mirror providers can also pick up the unstable version, and we would appreciate any support from mirror providers in that direction. I am not that much thrilled about the kind of solution I found as it doesn't solve the actual problem but rather "enhances" a perfectly working part of the code with some special cases. The actual problem lies within TriangleJRS, the triangulation code of TerraGear, which - as several checks have shown - is not as robust as advertised regarding computational geometry predicates. The "point-in-triangle"-detection-code does seem to have problems if the respective point is pretty near to the contour of the triangle. While the point is perfectly inside the triangle, TriangleJRS cannot detect that. The points are used to mark polygons and their associated triangles with associated attributes, including texture. As TriangleJRS does associate some of the points with adjacent triangles, texture attributes spill out into adjacent polygon areas. This is most noticeable in places where sea/ocean area is transferred into land this way. Fixing TriangleJRS was not possible for me as I am clearly not a computational geometry man. I will try to contact Jonathan R. Shewchuk on this issue, after some further analysis. The triangle package should be based on arbitrary precision predicates, as far as the documentation goes, but maybe I misunderstood what is meant by this ... or the predicates don't actually deliver to this promise. I have modified the algorithm to ensure that the selected points are at least a given distance away from the contours. Unfortunately, the new algorithm is less robust than the old one and might outright deny working on some specific valid, but degenerate polygons. Further, the distance used had to be selected arbitrarily according to the results of the scenery generation, but should be a safe estimate. The new algorithm has the advantage that instead of silently delivering points inside the polygon which TriangleJRS cannot handle, it will either deliver a "good" point or fail completely, resulting in an abnormal exit of the building process for the respective tile. I would appreciate if anybody wants to review my changes. The current version is available via git from http://mapserver.flightgear.org/git/terragear-cs/ Look into src/Lib/Geometry/poly_support.cxx, function calc_point_inside() (around line 447). Cheers, Ralf ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
