Holger and fellows

[Guest stentor]

Needing support: I have some simple questions about mesh terrainmanipulation data. Could you help me? Thanks by attentionCelso Junior - Brazil

[Holger 0]

Hi Celso:feel free to ask your questions whenever you're ready I'm sure someone here will try to answer them.Cheers, Holger

[Guest stentor]

Holger, hi again: The point is: INF file.1) SRTM.HGT, is it a RAW? Resample.exe doesn't manipulatea RAW directly. I suppose we must convert it to DEM.2) What format is a DEM?3) What is the difference between INF generate by Matthew's program (-32767)and the conventional (-9999).4) What -32767 really tell to Resample?5) What is the relation -9999 with ScaleInMeters?6) Why number of pixels+1 (1201)? And so on. Holger, the problem is: I dont't like do things ifI'm not understanding how it works. Microsoft explain such way only a wizard (they have THE POWER)can undestand. If you can help me, I'll be very grateful. Sorry by thebad english.Celsofrom Brazil

[Holger 0]

Hi Celso:I suggest you download an read Christian Stock's "Terra Model File Manual", tmf_manual.zip. It's a well written and concise summary of the different aspects of the surface features of FS.Regarding your specific questions:1. SRTM data have their own file format, called .hgt. Several utilities (MicroDEM, SRTM2BGL, 3DEM, etc.) have the required I/O (input/output) procedures to be able to read and/or write this format. 2. Not sure what you mean here, MicroDEM's internal .DEM format or digital elevation models in general?3 and 4. The NullCellValue parameter in the .inf file is meant to help Resample.exe deal with missing data in the source file. Missing data are typically set to a value that is unlikely to occur in the real world, such as -9999 or -32767. Obviously, your FS mesh should not have missing data; that's why it's important to make sure that MicroDEM, SRTM2BGL, or Blackart completely fill in/interpolate all holes in SRTM before using Resample.exe. However, if Resample does encounter the NullCellValue it will set this value to 0m, if I'm correct.5. Good question. It's possible that those values could be changed if you use bigbsq.exe (or Mdem6bsq.exe) with a ScaleInMeters value other than 1.0. Another reason not to submit files to Resample that have missing data.6. FS uses the mesh grid vertices (the nodes where the vertical and horizontal gridlines cross each other) to construct the visible surface, not the grid cells themselves. A single cell has two bounding vertical (and horizontal) gridlines, two cells have three bounding lines (left, center, and right), and 1200 cells have 1201 bounding gridlines. Hope this helps.Cheers, Holger

[Guest stentor]

Holger,hi: Thanks a lot by your explanations. Now I'm lessignorant about such format files. Some questions more:1) Why change HGT format to BSQ format?2) Matthew Styles's program generate a row of INF files. Is this INF configuration adequated for BSQ? The question about DEM format, yes should be about DEMgenerate by Microdem.So:3) Has a DEM a header? Sorry if I'm using too many your time. Thanks byattention.Cheers, Celso.

[Guest luissa]

> Holger,hi:>> Thanks a lot by your explanations. Now I'm less>ignorant about such format files.> Some questions more:>1) Why change HGT format to BSQ format?>2) Matthew Styles's program generate a row of INF files.> Is this INF configuration adequated for BSQ?>> The question about DEM format, yes should be about DEM>generate by Microdem.So:>>3) Has a DEM a header?>> Sorry if I'm using too many your time. Thanks by>attention.>>Cheers, Celso.>Celso,Here are 2 points on questions 1 and 3:1) I do not know what BSQ stands for (is it binary signed ... ?) but the "raw data file for the MS resampler" are a simple 2 dimensional array of altitudes in 16 bit (2 bytes) format. The points in the array (grid) should appear in the file from left to right (west to east) and from top to bottom (north to souht). HGT files are 1201 x 1201 x 2 bytes corresponding to the 1201 by 1201 spaced (by 3 seconds) altitudes that exist in a 1 degree square of latitude/longitude.So BSQ and HGT are similar. They can only differ in the meaning of the most significant byte. In order to use an HGT file as a raw file for the MS resampler you need to use:Type = ElevS16MSB in the INF file.3) I only know about the DTED2 DEM format. In this case there is a long header telling you a lot of information about the data. Even in this case the altitudes are coded in 2 byte numbers as in HGT. When I work with BSQs (converted to ElevS16LSB) I write at the end of the file the latitude and longitude of the NW corner and the number of columns and rows of the data. In that way I do not need to look to the name of the file (as in HGT) to know what data I am working with. And that makes the job of combining different files easier.Um abra

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[Guest luissa]

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