[gdal-dev] Converting USGSDEM into GTOP30 DEM or DTED

[Even Rouault]

Yes, this is possible but you need to adhere strictfully to the DTED 
specification. A DTED tile covers exactly a 1 degree x 1 degree area and the 
corners coordinates must be aligned on integer. As far as I remember, DTED0 
has a 30 second x 30 second resolution below latitude 50°, 60'' x 30'' 
between 50 and 70, 90'' x 30'' between 70 and 75, etc (read the spec). 

So you will have to produce several DTED files if your input area is over 
several 1° x 1° square. You should use the -prjwin to just select the right 
area for each tile, like :
gdal_translate -of DTED input.dem n40e2.dt0 -prjwin 41 2 40 3
gdal_translate -of DTED input.dem n40e3.dt0 -prjwin 41 3 40 4
etc..

With a little of scripting (Python for examle), you could automate that by 
reading the extent of the source .

You must be sure that your source input has the same resolution as the 
produced DTED, otherwise you'll need to adjust it by specifying the right 
destination size with -outsize 1201 1201 (below 50° latitude).

I see in GDAL source tree that there's a (not compiled) utility that seems to 
do you want. The main file is frmts/dted/dted_test.c, but it relies on the 
other C files of the DTED driver. You would need to fiddle a bit with the 
makefiles and the header to compile it (I see that some necessary symbols 
might not be exported). It is moderately involved provided that you have some 
experience with C.

But if your third-party app supports 16bit GeoTIFF as a possible source for 
DEM, it would be easier to translate to GeoTIFF.

Also by reading the documentation of the EHdr driver, I see GDAL can read 
GTOPO30 through the EHdr driver. So it could be possible to take the output 
of the EHdr driver as a GTOPO30 data (no guarantee ...), but we only output 
one kind of EHdr data which is maybe not the layout of GTOPO30. You would 
need checking the GTOPO30 spec too.

Even

Le Friday 13 March 2009 12:38:20 İsmail Dönmez, vous avez écrit :
> Hi all;
>
> I have a rather big (3.1G) USGSDEM file. I need to convert it to
> GTOP30 DEM format or to a series of DTED files to be read by a 3rd
> party library which does not support USGSDEM files. I looked around
> and apparently gdal does not support exporting to GTOP30 DEM format.
> So I wonder if there is a way to convert USGSDEM file into a DTED file
> which will cover _all_ area, ie.
>
> gdal_translate -of DTED input.dem out.dt0
>
> just creates a one point with 1201x1201 area.
>
> Any help is appreciated. Regards.