Re: [Flightgear-devel] Shader optimization

[Frederic B. <fre...@fr...>]

> De: "James Turner"
> 
> On 16 Oct 2012, at 13:38, Tim Moore wrote:
> 
> > The tile data on disk is actually stored in a
> > coordinate system that is aligned with the earth-centric system, so
> > Z
> > points to the north pole. We rotate the coordinates back to a local
> > coordinate system because that provides a much more useful bounding
> > box for intersection testing and culling... and also lets you
> > program
> > snow lines in shaders :)
> 
> Uh, are you sure about that? My understanding is that the BTG coords
> on the disk are in 'tile local' coords, i.e 'Z is up'

BTG are in cartesian coordinates and are rotated at load time here :
http://gitorious.org/fg/simgear/blobs/next/simgear/scene/tgdb/obj.cxx#line923

Regards,
-Fred