2007 September 07
A free Canada-wide 1:50,000 elevation model.
This project was in preparation of sending a Canada-wide elevation model to Google Earth and NASA World Wind. It was completed a couple of years ago, although the data is not yet generally available through those tools — thus the reason for hosting it here:http://sydney.freeearthfoundation.com/mattwilkie/draft/canada_50k_dem
(thank you Adam Nowaki and the Free Earth Foundation!).
note: hostname has changed to http://s1.static.tileservice.net/mattwilkie/draft/canada_50k_dem/
The data are marked draft because only a very preliminary review of the resulting mosaick has been done. There is no guarantee the data is complete or faithfully represents it’s source. I am interested feedback on the product and it’s utility but I make no promises that any problems identified will ever be rectified. Of course I will happily post your fixes here, should there be any!
Process used to create this version of the Canada 50k DEM:
1. Download 1:50,000 Digital Elevation Models for all of Canada from Geobase.ca. Some of that process is described here at the YukonGIS.ca wiki, basically a lot of:
wget –continue –recursive –level=2 –no-host-directories –cut-dirs=3 \ ftp://ftp.cits.rncan.gc.ca/pub/geobase/1129608060/cded1/
2. Unpack the dems and mosaick into larger more manageable chunks (unzip_dems.bat, dem2tif.bat). Essentially:
:: Unpack
for %%a in (%tiles%) do ( unzip -d %%a %%a/\*.zip \*.dem )
:: Mosaick
gdalwarp -srcnodata -32767 -dstnodata -32767 \
-co compress=lzw -wm 1024 -rc -wo init_dest=no_data -multi \
-t_srs nad83 %srcdir%\*.dem output.tif
3. Using gdalwarp like this builds a much larger file than needed, so we compact down to more optimal size with:
for /r %%a in (*.tif) gdal_translate -co compress=lzw %%a d:\packed\%%~nxa
And that’s about it. Some fifteen thousand ittty bitty elevation models are now in only 71 larger files.