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View Full Version : DEM Files? Converters? What?


mdunakin
07-14-2005, 05:15 AM
Just curious, but how do you get a DEM file?
I have always wanted to look at DEM files, ever since I've owned LW, but yet, whenever I
go to one of those sites that I hear so many people always refering people to, all I ever see
are files that are NOT DEM files, but some other weird file name, and I have never been able to figure out how you actually GET a DEM file?

Like at this site:
http://data.geocomm.com/catalog/US/61069/2381/group4-3.html
It "says" DEM, but in reality, they're something else.
And when you decompress them, their something else, like a "bunch" of files.
But none of them say DEM on them, so what do you do to convert these into DEMs?

I was hoping that I could just go to USGS or something and
download away and then load up some DEMs and render away!

Anyway, trying to figure out, from all the zillions of programs they show at that site I
have listed above, if any of them will create DEMs for me so i can load them into Vue?

So far, I have no clue what I'm looking for LOL

Anyway, thanx............md :)

royboy
07-14-2005, 06:00 AM
Unfortunetly DEM files dont seem to be standard, the two common ones are SDTS & USGS. I know vue can only read one type correctly - think it was the USGS. Ive had good success using geotiff or hieght field bitmaps, but the z value is based on a greyscale value btwn 1-256 so the hieght value sometimes has to be tweaked. www.vterrain.org (http://www.vterrain.org) has some good advice..

BernieS
07-14-2005, 06:16 AM
DEM files are a standard for geological data files, and I have imported them directly into V5I without too many problems.

As for where they may be found, here is a selection of sites to get you going ... ...

Go here:

http://www.visualizationsoftware.com/3dem/downloads.html

for an extremely useful & free utility for converting files to dem format. The site also contains links to sites where dem files may be found.

Go here:

http://members.fortunecity.com/eco4/giseco/id8.html

for a site containing links to other dem sites.

Go here for the USGS dems:

http://edc.usgs.gov/geodata/

Go here:

http://duff.geology.washington.edu/data/index.html

for the University of Washington digital file library.

Go here:

http://www.reo.gov/dem/

for dem files covering Oregon & Washington state. Note that the files are listed by goegraphical co-ordinates, not name, so it may take a bit of work if you're looking for something specific!!

Have fun!

Bernie

mdunakin
07-14-2005, 09:09 PM
I "did" manage to get one DEM into Vue and it was really no problem, other then me trying to figure out how to make the actual DEM from whatever those files were that it originated from, with the extention of .ddf, which originatd from a compressed file that looked like this:

1662394.DEM.SDTS.TAR.GZ

And then that file made a ton of smaller files with the .ddf extention and a text file.
I ended up using this command prompt app to convert all of this into a DEM,
called, sdts2dem.exe which actually worked, though the DEMs end up with
like a wall around parts of it that I don't know how to get rid of?

Anyway, thanx for those links and I'm going to check them out right now.
I'm mainly looking for our local deserts and such, like from the Anza Borego Desert.
And other deserts in the south west end of the states, Navada, Arizona and California.

thanx again and this is fun!....................md :)

royboy
07-15-2005, 12:54 PM
To get rid of the walls around, you can save the grey scale bitmap from the terrain editor & edit with photoshop. The walls will be a light grey to white around the boundary. Create a black border over this which will to set the height to 0 around the edges. Probably easier than trying to edit dem files..

mdunakin
07-15-2005, 04:41 PM
Oh, OK, thanx!

I didn't even know I could send out a grey scale from the terrain
editor yet, as I haven't gotten that far into the program yet.
There is loads to learn, that's for sure :)
I'll check that and see how it works?
Thanx!............md :)

kivanc_k
07-22-2005, 12:19 AM
Lord Wexford posted a great reply, thanks for the effort.
More or less I`d say the same. Just a couple of rephrase with his permission :

1. Yes, SDTS and USGS dem has versions also, converters are lifesavers.
2. .tar.gz is a native, couple of compression extensions for Unix clones (including Linux -my lovely penguin-), which you can open with WinRar on "M$ : Win-those".
3. Read Lord Wexford`s posting at least twice and follow all the links (nvm some 404s).
4. There are 2 more very useful links of dem data I used and I wanted to post here but I couldn`t find my memory stick and I`m unable to reach my other machines at the moment, tomorrow (in 10 hours after this posting) I`ll send them here.

Thanks Wexford

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