Harald JOHNSEN wrote:
Alberico, James F wrote:
Hi,
I have been tracking down the cause of an FGFS access violation that
occurs when attempting to use 1-arcsec scenery data for a tile generated
in TerraGear to have 40000 nodes. Granted, this may be extremely
ambitious from a performance standpoint, and may prove to be completely
infeasible. However, I am very interested in knowing the current limits
and pushing hard on them.
Hi Jim,
It good to see some big names showing up on the list. This might give
the project a boost to get to the next level.
What I think I've learned so far from debugging:
1.) The FGFS FGBinObj reads with no errors.
2.) The access violation occurs during leaf generation.
3.) The breakage occurs shortly after the texture coordinate index
exceeds the max value of a short (32767) and goes negative.
4.) The symbols (e.g., tris_tc) that carry the read-in indices are of
type int
5.) Examination of the TerraGear bin writes, and the FGFS reads reveal
the indices are stored as short types.
6.) So, my conclusion is the scenery of the 1-arcsec tile is limited
to 32767 nodes. (or maybe polygons?) And, TerraGear will truncate any
index above that when writing to the binary
file.
I'm a newbie to TerraGear/FGFS details, so please correct me if I'm
wrong about any of this.
At this point Curtis is the one who is most involved in these things. He
is attending the MathWorks International Aerospace and Defense
Conference 2005 and will be back tomorrow. It might be best to send him
a private copy of your mail also.
I would appreciate any comments on what mess might result from any
attempt to store/read ints, rather than shorts, to expand the scenery
resolution. From a performance standpoint, the capacity of the short
type may far exceed anything practical at the present time. Comments on
that aspect are welcome, too.
I think that the only side effect will be that your new binary will be
incompatible with current scenario files,
perhaps that changing short to unsigned short could be enought.
Curtis already mentioned he wanted to change the layout of the tiles
which probably breaks backward compatibility. So if it would be
necessary this change could be adopted as well.
Erik
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