Does size of mesh bgl files matter?

[Holger 0]

Hi all:I'm working on a LOD8 replacement terrain mesh for a large area, about 1 million square miles. The resulting bgl files will be about 120MB unzipped; however, I believe that the download will be worth it!My question is, is there a good rule of thumb to split up the entire mesh area into smaller tiles? I am not referring to the LOD quadrant system; I'll be carving the tiles to fit the LOD 8 quadrants. I wonder about the best pick of tile size somewhere between a single LOD 8 tile (about 40km x 40km) and the whole area (1000km x 1000km). Currently, I have 9 files, each about 10-20 MB in size. I noticed, however, that if I move quickly between tiles, it takes my aging system (P3 750, 256MB, Radeon 8500) quite awhile to move down the LOD hierarchy to the LOD 8 level. I assume that FS will load the terrain bgl files into RAM as required, one at a time. If that's true, then smaller bgl files should be better. The downside is that I would spend a lot of time carving tiles and each tile would have to have some overlap to fit in with the LOD hierarchy, increasing the total download size.Before I embark on lenghty experiments - has anyone out there knowledge about this matter?Cheers, Holger

[Guest sgreenwood]

Hi Holger,I do not believe bgl file size will affect performance much; the sim only reads as much of these files as it needs at any one time. Convenient construction and/or downloading are more important considerations.The performance issue you refer to is due to the LOD you are using. Have you tried comparing it with LOD7 mesh? Increasing LOD ("oversampling") can add more detail, but it seems to reduce accuracy. You might try comparing both with some more accurate higher resolution mesh for the same area if possible. If you are interested in learning (much!) more about FS2002 file use, you might find this utility entertaining.Filemon v4.34: "This monitoring tool lets you see all file system activity in real-time. Versions exist for all versions of WinNT/2K, Windows 9x/Me, Windows XP 64-bit Edition, and Linux."available at: http://www.sysinternals.com/win9x/98utilities.shtml(Regmon v4.35: provides similar information regarding Registry access.)For example, when my confguration of FS2002 starts, it accesses the file system over 45,000 times before giving me control. I decided that adding or removing a couple of files was not going to make much difference in my startup time. :(Running the sim in window mode with this running along side will show you exactly what areas of your bgl files are being accessed, and how often. Very impressive.Regards,Stevewww.fs-traveler.com

[Holger 0]

Hi Steve:thanks for the feedback, and thanks for the highly useful mesh information on your web pages, which helped me a lot to get my head around mesh design!I'll try LOD7 and I'll try a comparison with a subregion, for which I have a 50-m DEM (the larger region baseline data is a 250-m DEM, so LOD7 (~300m) might be better anyway. I have done a comparison of the 50-m DEM (resampled to LOD9) with LOD10 and 11 resamples of a 25-m DEM for the same area; the higher res LODs look better only in close-up screenshots and most of the gain in detail is masked by the salt-and-pepper appearance of the surface textures (in this case forest). My conclusion in that case, which has been echoed somewhere else in this forum, was that LOD9 is the better choice for high-res meshes, both economically and with respect to in-flight appearance. I'll definitely check out the FileMon utility: 45,000 times - ouch! No wonder FS2002 puts more strain on my system than any of my statistics packages.Cheers, Holger