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analyzing dem bgl format

E

einsub

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southkorea
Hello.

I'm preparing develop scenery mesh tool and now analyzing demXXXX.bgl format to display default fsx mesh.
I could understand basic bgl format which is composite of header and several sections but actual data section is difficult to understand.
Another type of bgl format seem to be analyzed already, but I couldn't find any resources which explained this dem format.
If does anybody know the useful link, please inform me.
Sorry for poor English.

Your sincerely.
einsub.
 
Hi,

I think Jim Keir did some work on this in the past, but if I remember correctly he stopped on that. As far as I know no data on this is available.
 
einsub said:
Hello.

I'm preparing develop scenery mesh tool and now analyzing demXXXX.bgl format to display default fsx mesh.
I could understand basic bgl format which is composite of header and several sections but actual data section is difficult to understand.
Click to expand...

Yes, I suppose this will be VERY difficult to reverse engineer because the compression algorithms going into mesh compression are really state of the art:

Henrique Malvar developed some of these techniques used in FSX. That's serious engineering stuff at PhD level..

http://research.microsoft.com/~malvar/

So you may be able to figure out the structure of the container format (BGL), but the data portion will be hard to reverse engineer. Essentially you would have to rip out the entire decoding engine from FSX. Which might be legally dubious ;) You're likely dealing with a CODEC of similar complexity to JPEG 2000 ... frequency decomposition with techniques comparable to wavelets, probably multiresolution (hierarchical) coding, advanced entropy coding (e.g. arithmetic bitplane coding).

It might take weeks to come up with a working decoder even if you had a specification.
 
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