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 tohttp://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.