[Freegis-list] 3CD or 3TX data

Davide Borelli emo.da at jumpy.it
Fri Mar 10 15:05:04 CET 2006

I think INM gives an overflow error 'cause 15 3tx files are really too many!
For my study I used 2 of them, and in INM's example study there's only one of them!
As you can see in INM's manual, a .3tx file contains terrain elevations covering a one-by-one degree area. 
Below there's a description of the .3tx format.

The .3tx ASCII text format:

Lat Long

-Lat    is the latitude of SW corner (integer degrees)
-Long  is the longitude of SW corner (integer degrees)
-elevation is terrain elevation MSL (integer meters)

The first line in the file defines the southwest corner of the one-by-one degree area.
North latitude and east longitude are positive integers; south latitude and west longitude are negative integers. The SW corner must be on integer degrees.
There must be exactly 1201*1201=1442401 lines following the first line. Each line contains one number - the elevation, in integer meters, of the terrain
above mean sea level. The elevation of the SW corner is the first integer, the elevation that is 3 arc-seconds to the north is the next integer, and
so on until the top edge (integer degree latitude) is reached. Then move 3 arc-seconds to the east, start at the bottom edge, put in another 1201 elevations while moving north, and so on until the file is finished.
The binary format (.3cd) is sold by Micropath for U.S. regions; non U.S. users must manually write their .3tx ASCII text file, which INM software reads and converts in a .3cd binary one, where the name is given by the Lat/Long specified at the first line of the .3tx file.

After that, INM converts ALSO the .3cd file into a "terrain.bin" one, so with all these conversions is easy to have an overflow!

One important thing is to export in the right way filling unknown areas in the elevation data, to do so follow these steps (I used the "Europe" data at http://www.ngdc.noaa.gov/seg/fliers/se-1104.shtml):
-drag Europe.hdr in VTBuilder window;
-Click in "Area Tool"--> "Numeric values" and fill "Origin and
Size" with, for example (12,00000000, 57,00000000), (1,00000000, 1,00000000), then click "ok"
-Go to  "area tool"-->"Merge & Resample Elevation", select "Output"-->"To File" and give as name N57E012 and desktop as destination folder; then put in "Sampling"-->Grid Size" put 1201 in both fields and press again "ok"; you'll find on the desktop two files: N57E012.bt and N57E012.prj
-Close VTBuilder;
-open it again and drag inside the windowi N57E012.bt;
-Click on  "Elevation"-->"Fill in Unknown Areas" (this is very important!)
-At last: "Elevation"-->Export to..."--> 3TX

Now try to import this file in INM, then do the same with every 3tx you need, changing the coordinates, of course!
INM should give no problems this way (I hope...!). 


  ----- Original Message ----- 
  From: Michael 
  To: Davide Borelli 
  Sent: Friday, March 10, 2006 2:09 PM
  Subject: Re: [Freegis-list] 3CD or 3TX data

  Hej Davide!

  Thanks for the links, I downloaded some files covering the surrounding 
  of my airport. You were right about FAA's INM that's exactly the tool I 
  am working with! And you said I could ask you if I got any questions... 
  In fact I got some. I have a total of 15 3TX files generated with 
  VTBuilder (http://vterrain.org/Doc/VTBuilder/overview.html) from the 
  downloaded data and wanted to import them into my INM study. I just put 
  them into a directory and imported them, but doing it this way all parts 
  will be in the same small rectangle and I got 15 layers one on the 
  other. Then I tried to enlarge the rectangle, according to the 
  dimensions I got. 3 rows with 5 squares each and each tile one by one 
  degree gives a rectangle of about 286km x 337km, with a offset for the 
  lower left corner according to my coordinate references. However doing 
  it like this INM always crashes due to an overflow...
  Do you got any idea what I am doing wrong or how to do it??? I would be 
  very happy about any information you can give me. Do you perhaps know 
  some tutorials or workshops which are available on the web for INM? I 
  didn't find anything useful...

  Thanks in advance!

  Cheers and Greetings from Stockholm!

  -------- Original-Nachricht --------
  Von: "Davide Borelli" <emo.da at jumpy.it>
  An: freegis-list at intevation.de
  Betreff: Re:[Freegis-list] 3CD or 3TX data
  Datum: 09.03.2006 09:51

  > Hi!
  > I suppose you're using FAA's INM, isn't it?
  > I've just finished my bachelor thesis on it and HNM!
  > For the data, you can try ftp://e0srp01u.ecs.nasa.gov/srtm/version2/Eurasia
  > these are SRTM files and you can learn about them at 
  > http://www2.jpl.nasa.gov/srtm/
  > I see there's not much Sweden data, so maybe, if you don't find what you 
  > need, you can use the "Europe" data at 
  > http://www.ngdc.noaa.gov/seg/fliers/se-1104.shtml and obtain 3tx files 
  > from it!
  > Write if you have problems
  > Davide
  >     ----- Original Message -----
  >     *From:* Michael <mailto:geckonews at web.de>
  >     *To:* freegis-list at intevation.de <mailto:freegis-list at intevation.de>
  >     *Sent:* Wednesday, March 08, 2006 11:04 PM
  >     *Subject:* Re: [Freegis-list] 3CD or 3TX data
  >     Hej Ben!
  >     Thanks a lot for the link! Now I just need the data...
  >     /Michael
  >     P.S.
  >     Sorry for the quite weird sender. I usually don't send e-mail from
  >     this address but only receive. Now I changed it to something useful.
  >     -------- Original-Nachricht --------
  >     Von: "Ben Discoe" <ben at vterrain.org <mailto:ben at vterrain.org>>
  >     An: freegis-list at intevation.de <mailto:freegis-list at intevation.de>
  >     Betreff: Re:[Freegis-list] 3CD or 3TX data
  >     Datum: 08.03.2006 21:37
  >      > Michael,
  >      >
  >      > The free software VTBuilder can read elevation data from any
  >     format and
  >      > export it to 3TX.  Therefore, you should not have to worry about file
  >      > format, as you look for data.
  >      > http://vterrain.org/Doc/VTBuilder/overview.html
  >      >
  >      > -Ben
  >      > http://vterrain.org/
  >      >
  >      >> -----Original Message-----
  >      >> From: Gecko's News Adresse
  >      >> Sent: Wednesday, March 08, 2006 5:34 AM
  >      >>
  >      >> As an input for
  >      >> the simulation program I have to use, I need topographical
  >      >> data. Therefore I am searching for a source of such data for
  >      >> Sweden, which is provided or can be converted into the 3CD or
  >      >> 3TX format.
  >      >> Does anybody of you know where I can find such data?
  >      >
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  >      > Freegis-list mailing list
  >      > Freegis-list at intevation.de <mailto:Freegis-list at intevation.de>
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