Hi,
DEM's cover entire landscape areas, often thousands of square miles. Towns are a few square miles, and even most cities only a few dozen. The biggest problem is actually locating where towns/cities ARE on the DEM because there's no aerial imagery to guide you!
To get the imagery (raster maps) for a particular town, you need to know WHERE the town is to start with. OK, you can use Map Tile Servers or Web Mapping Services to do that, but it's slow and you have to download a LOT of raster maps in stages to follow the route using the Simple Route Editor. You can use a route as a mapping path for rasters, but TransDEM fails on that if the route is too complex.
I've figured out a much easier way to do things...
The latest version of TransDEM (v2.1.2) supports import of Google Earth KML/KMZ files as vector data. This means you can draw paths accurately following railway tracks in Google Earth (GE), where you're working with aerial photography already and can fly around plus zoom/in out very easily.
Once you're done, you can export the complex path (usually a whole GE folder containing multiple paths) as KMZ, and that's now the "full" route you'll use in TransDEM. But it's usually too complex. There's a way around that as well...
Just draw a simple "mapping" path in GE roughly following your complex path (using as few paths and points as possible), export that to KMZ as well, import into TransDEM and use IT along with the "obtain images along path" feature to obtain ALL your raster maps in one fell swoop. If you want images further from the route, draw parallel paths either side in GE before exporting. You'll have to experiment with separation distances, to avoid obtaining too many raster maps.
Once you have your raster maps in place, close the "mapping" route and import your "full" route. If you drew the "mapping" route correctly, the "full" route should lie completely within the raster-mapped area. You're now ready to select a rectangular area and export DEM data, vector data or UTM tiles to Trainz.
And all that without ever touching TransDEM's Simple Route Editor! That's because the beauty of Google Earth is that it can be used as an Advanced Route Editor complete with fast-streaming aerial imagery!
There's a slight problem, though. I organise routes by folders in GE and TransDEM will sometimes unexpectedly terminate to the desktop without error on importing a particular KMZ (or KML) file. I'm then forced to re-run it then re-open my DEM and raster maps again, etc. But every time I try to import the KMZ/KML file, TransDEM bombs out again.
I'm still trying to figure out exactly what's causing this "bug", but I strongly suspect it's to do with TransDEM exceeding a limit on how far down it can parse nested folders in a KML/KMZ file, and having no error trapping in place to handle it. If I flatten (simplify) the folder structure in GE so the exported KMZ/KML is no more than about 3 or 4 folders deep, TransDEM doesn't bomb out on importing. This behaviour is causing problems because my GE folder structure IS a complex nested one, which I'm now having to completely restructure so TransDEM will remain stable.
Maybe geophil can shed some light on this?
Hope this helps you all create better routes more quickly.
