TransDEM Forum

:?: Dear Roland

I have been importing DEMs from a Norwegian site as follows:

http://data.kartverket.no/download/content/velkommen

I get the dowloads OK (in zip files) but when I try to open the DEMs in TransDem (64) I get the error "Error reading DEM!"

Is this likely to be a similar problem that the post "TransDEM has problem with some Canadian DEMs" showed in February this year? Or something else entirely?

Grateful for any answer you can give..

Thanks
pdw

Well, that's easy to explain. The only zip format TransDEM can read as DEM is SRTM. And the only file types supported with the .dem extension are either MicroDEM .dem (default in TransDEM) or Canadian CDED. The kartverket.no DEMs appear to be zipped files of an ASCII type .dem, which does not resemble any of the formats TransDEM supports so far.

I have a few language problems with the kartverket.no website, but the resolution of those DEMs looks very promising. However, I need more information on the file format to be able to implement it in the next version of TransDEM, preferably in English.

I did some investigation. The clue was "Format: USGS DEM". This did not ring any bell at first. When I started working on TransDEM in 2003, USGS had its cumbersome file format "SDTS" which they later retired and replaced with more middle-of-the-road industry standards for NED. But then I remembered that the Canadian CDED specs had mentioned that their format was based on an earlier USGS file format and I used these specs to compare the individual fields with the actual data in the Norwegian DEM. The Canadians have made some minor amendments and small changes to the original USGS format and the TransDEM implementation is based on the CDED specs. CDED DEMs are always in geographic coordinates but the original format allowed for UTM projected coordinates as well, northern hemisphere only and North American or WGS84 datums only, but that would do to be able to read the Norwegian DEM.

Here it is now, a small section of the Bergen Line, near Bolstadøyri.

DEM alone:



DEM with 1:25,000 topo map, acquired via WMS:




The enhanced CDED DEM interpretation will be available in the next version of TransDEM, most probably as an update to 2.5.

I am working on expanding some Norwegian routes now, using this WMS service. Do you remember how you managed to acquire the 1:25,000 topo map, acquired via WMS? There are many data sets on the web site..

Thanks pdw

I just checked. Apparently that clipping is not 1:25,000 but rather 1:50,000 and it most probably came from this WMS:
http://openwms.statkart.no/skwms1/wms.toporaster2

Norwegian DEM's still don't work for me, even with the latest version. Would love if someone could look into it.