> ----- Original Message ----- > From: "Lee Elliott" <[EMAIL PROTECTED]> > To: "FlightGear developers discussions" > <flightgear-devel@lists.sourceforge.net> > Subject: Re: [Flightgear-devel] obj->ac conversion question... > Date: Tue, 19 Sep 2006 20:40:36 +0100 > > > On Tuesday 19 September 2006 14:10, Jeff Koppe wrote: > > Hi All, > > > > I've been making/texturing a aircraft model in Wings3d, > > exporting to .obj and using Blender to convert to .ac. But > > since either the Blender .obj import or .ac export is not > > perfect, this workflow requires some tweaking of the final .ac > > file. So I figured I'd cut out the middleman and write a Ruby > > script to convert .obj to .ac. > > > > Now the question: neither .obj nor .ac formats specify three > > or four sided polygons. Does FlightGear? Blender does > > (imperfectly) triangulate/quadrangulate the model but I'm not > > sure why--I imagine it's a holdover from .3ds format. If > > FlightGear does not _require_ triangulation, then is it more > > efficient? > > > > Thanks, > > > > --jeff > > Heh:) I cobbled together a rough C prog to convert .obj geometry > in to .ac format but I didn't look into the texturing aspects > because all I wanted was the geometry. It became redundant when > I got the .obj importer for ac3d. > > Afaik both .obj and .ac formats support n-sided polys whereas I > believe that the .3ds format only uses triangles. Everything > I've ever exported in .3ds format has been converted to tris. > > I don't know if using polys with > 3 sides is more efficient but > the most important consideration is that a triangle will always > be perfectly flat whereas polys with > 3 sides may not be > because all the points don't have to be in the same plane. > > The renderer that FG uses actually converts all polys into tris > and this means that a curved poly, where the points are not all > in the same plane, can be interpreted, or split into two tris, > in two different ways, producing entirely different surface > shapes. > > Imagine a four-sided poly with it's vertices at: > > (hope this looks ok) > > (A)0,0,0 (D)1,0,0 > > > (B)0,1,0 (C)1,1,1 > > > If this poly was split into two tris by adding an edge between B > and D the path between them would be straight but the path > between A and C would be curved. However, if you put the edge > between A and C instead then the path between B and D would be > curved instead, changing the shape of the poly completely. > > Afaik the renderer decides on how to split n-sided polys into > tris is based on the vertex order and this can sometimes > produces rendering glitches where it curves a poly in the wrong > direction (or at least not the direction intended by the > modeller). > > Ways around this are to either re-order the vertices or manually > split the poly into tris. > > LeeE > > > ------------------------------------------------------------------------- > Take Surveys. Earn Cash. Influence the Future of IT > Join SourceForge.net's Techsay panel and you'll get the chance to share your > opinions on IT & business topics through brief surveys -- and earn cash > http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV > _______________________________________________ > Flightgear-devel mailing list > Flightgear-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/flightgear-devel
> Thanks LeeE. Since FG splits the geometry into triangles anyway, I'm probably better off using Wings' tesselate command to help it out. Though I might do some experiments to see how well FG tesselates on its own. It's been my experience that this is often best done when modelling rather than rendering. But I might be in for a nice surprise... --jeff -- _______________________________________________ Surf the Web in a faster, safer and easier way: Download Opera 9 at http://www.opera.com Powered by Outblaze ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
