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Guest cbuchner1

Going from USGS Seamless Server to BGL format. Any tutorials?

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Would there there be any tutorials available how to process elevation data (e.g. NED 1/3 arc second) downloaded from USGS seamless servers into BGLs for use in Flight Simulator?For the output format I selected:Output Format: BILNAD 83 GeographicX cell Size: 00.00009 DegreesY cell Size: 00.00009 DegreesI suppose NAD 83 format requires some reprojetion to WGS 84. I could also have selected GeoTiff or GridFloat format, all of which are in floating point. Now the big question is which free software could I use for reprojection...For the moment, I am just trying to get a Bryce Canyon at 10m resolution. But maybe later I want to cover larger areas and figure out how to make evelation meshes streamable in tileproxy... umm...Any pointers in the right direction would be helpful.Christian

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Hi Christian,old thread but still valid: http://forums.avsim.net/dcboard.php?az=sho...ing_type=searchFor 10-m data you may want to work with the FractionBits parameter to get sub-meter vertical resolution and avoid terracing effects; see the Terrain SDK. General background on FS mesh design (some of it has changed for FSX) available at Steve Greenwood's old site: http://home.earthlink.net/~smgreenwood/welcome.shtmlCheers, Holger

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Excellent.NAD83 is essentially WGS84 with very minor (neglectable?) differences according to this: http://www.mentorsoftwareinc.com/resource/Nad83.htmSo a reprojection does not appear to be necessary. In essence a download from the Seamless server can be turned into a BGL very easily and quickly. I supposed this could also be done by Tileproxy in an automated way, except that the terms of use of the Seamless server may not allow scripted access.

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lol, I just searched on Google for "usgs seamless terms of use" and the FIRST hit was this very thread which I started not an hour ago.Blast, Google is QUICK.

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>Excellent.>>NAD83 is essentially WGS84 with very minor (neglectable?)>differences according to this:>http://www.mentorsoftwareinc.com/resource/Nad83.htm>>So a reprojection does not appear to be necessary. In essence>a download from the Seamless server can be turned into a BGL>very easily and quickly. I supposed this could also be done by>Tileproxy in an automated way, except that the terms of use of>the Seamless server may not allow scripted access.>>Not so fast, my friend.... Learn from my efforts of a few weeks back, you do need to reproject as even with no significant variance between NAD83 and WGS84, there's this very picky program called Resample which must, I repeat must be fed only WGS84 - Geographic files.The other particular thing to be careful of, OK, two things, first is the fractional bits setting, which samples or smoothes the terraced look of mesh. A setting of greater than 2 will run you out of elevation data ranges if you're not careful. I used a FB setting of 3 and found some "holes" in my mesh at the top of two mountains. The setting of 3 gives you -4096m to +4096m and my two little mountains just happen to be just above 4,096m. Resample gave me two 27,000 holes where the mountain peaks were suppose to be....The other comment I would make is use the compression setting. IIRC, mine is at 85% and the file size savings is significant.And a freeware tool to look at the GeoTiffs and reproject that I've used is called MapWindow; http://www.mapwindow.com/

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I suppose I can tweak RESAMLE.EXE into accepting the BIL file directly, as it is just 2 byte integer variables in little endian order. I remember seing an INF file for RESAMPLE in some forums that could directly accept the BIL file as input.I have no intention to provide a GeoTiff to RESAMPLE.

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It`s the download size. BIL format is about twice as efficient as any floating point based format. So I can get all of USA quicker ;) Will still be around 90 GB or so. Ouch.I will just have to interpolate out the terracing effect that I get from vertical sampling at integer 1 meters in the BIL source data.Christian

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