http://www.tt-forums.net/viewtopic.php?f=29&t=27052
It's actually a link for a way to create maps for the game transport tycoon however i feel the bits at the begining of this guide could still be of use for some?
Well if you can make heightfields as it suggests then you can use it for Terragen 0.9 or 2.
Just been playing with it ; I'm not sure if the DEM's that come with Google Earth are detailed enough!?
Where can you download detailed DEM files?
Have you tried the one from Microsoft Virtual Earth?
Here's a few of my favourite free data sources. Resolution varies with high res data with many countries only being available at commercial rates. Canada and the US have the best data availability, although even Canada's varies from territory to territory.
Elevation:
US: http://seamless.usgs.gov/website/seamless/viewer.htm (http://seamless.usgs.gov/website/seamless/viewer.htm)
Canada: http://www.geobase.ca/ (http://www.geobase.ca/)
Global SRTM3 (Google Earth index): http://www.ambiotek.com/srtm (http://www.ambiotek.com/srtm)
Global Bathymetry: http://www.ngdc.noaa.gov/mgg/global/seltopo.html (http://www.ngdc.noaa.gov/mgg/global/seltopo.html)
Crater Lake Bathymetry: http://oregonexplorer.info/craterlake/bathymetry.html (http://oregonexplorer.info/craterlake/bathymetry.html)
Great Lakes Bathymetry: www.ngdc.noaa.gov/mgg/greatlakes/greatlakes.html (http://www.ngdc.noaa.gov/mgg/greatlakes/greatlakes.html)
Imagery:
Global Landsat: https://zulu.ssc.nasa.gov/mrsid/mrsid.pl (https://zulu.ssc.nasa.gov/mrsid/mrsid.pl)
Global Blue Marble: http://www.celestiamotherlode.net/catalog/earth.php (http://www.celestiamotherlode.net/catalog/earth.php)