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Holger

A Question abot TMF Files?

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SRTM Data around large cities messed up. (Maybe due to "Skyscrapers")

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Hi there:could you be a little less specific, or is this meant to be a riddle? ;-)Q1: no, you can't edit .tmf files, though you can use MicroDEM and other GIS software to (hand-) edit the SRTM source data (.hgt format).Q2: indeed, tall buildings introduce 'noise' in the radar signal, depending on the angle of 'illumination' (by the radar beam) and whether it's a single structure or an entire downtown core. Also, if the radar beam hits a smooth surface it might get deflected in different directions rather than reflected back to the emitter (the satellite). Below is an SRTM 1-arcsec image of Chicago (N41W088.hgt) I loaded with MicroDEM and then enhanced in Photoshop. Notice the elevated Interstates radiating from the downtown core. The core itself is largely missing, probably due to the backscatter I mentioned above. Lower buildings and smaller clusters or individual structures can be spotted as reddish 'bumps'. Pretty interesting but not very desirable for FS mesh making ;-)Of course, for the US the work-around is to cut out the offending area and to merge in USGS DEM data; for other countries without alternative high-res elevation data I'd suggest DTED0 or GTOPO30 data for merging. In the specific case of Chicago it's probably fine to compile the SRTM data as is and then place a flatten switch on top of the entire city area.Hope I managed to answer your questions!?!Cheers, Holgerhttp://forums.avsim.net/user_files/36788.jpg

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Okay, Thank you! One more question, is it possible to get the MicroDEM *.DEM back into SRTM *.hgt format?

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nope, not that I know of. MicroDEM has limited export functionality, though for processing with the MS Terrain SDK utilites the .DEM files can be processed with John Childs' bigbsq.exe utility or (in the latest version) directly saved in the 16-bit BSQ format that resample.exe requires. If you use Steve Greenwood's LOD calculator it's quite straightforward to come up with the correct parameters for the .inf file.Cheers, Holger

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