All that weird stuff is quite easy to explain.  The binary .btg scenery
format uses 16 bit integers as indices for the vertex, normal, texture
coordinate lists.  At one point we were using signed 16 bit integers, but
I'm pretty sure we sneakily changed the flightgear btg loader to use
unsigned 16 bit ints.  So this changed the original limitation of a max of
32,768 vertices/texture coords/normals, etc. up to 65,535.  However, I don't
know if the terragear-cs tools ever got this fix on the scene generation
side.  So if your scenery exceeds these limits, this is exactly what you
will see.

The ultimate solution will be to expand the btg format to 3 or 4 byte
integers -- but that will again require changes in the terragear-cs tools as
well as changes in the flightgear btg loader.  Conveniently we have a
versioning system in the btg format so we can extend the format and maintain
backwards compatibility if we want.

The downside is that this index is used so much in the scenery files that
going to a larger int size will have an immediate corresponding proportional
impact on the btg sizes of all the files.

There may be other ways to tackle this problem too ... maybe the btg format
emitter could detect if the size exceeds the threshold of the current format
and output just the tiles that require the extended format in the extend
format.  (Sorry it's late friday, I hope that makes sense.) :-)

Curt.


On Fri, Sep 30, 2011 at 8:54 AM, James Turner <zakalawe@mac....> wrote:

>
> On 30 Sep 2011, at 11:56, Martin Spott wrote:
>
> > Hah, I managed to find the web page I've been searching
> > for weeks, Bruce did a pretty nice writeup of the problem:
> >
> > http://www.cullam.com/flightgear.htm
>
> A very useful description, yes!
>
> James
>
>
>
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--
Curtis Olson:
http://www.atiak.com - http://aem.umn.edu/~uav/
http://www.flightgear.org - http://gallinazo.flightgear.org