I'm spinning my wheels trying to find an existing, free source for TMS or WMS elevation data that doesn't involve a long-winded clickabout or an emailed url. This question has a similar purpose, but the answers offered aren't compatible with what I want to accomplish.
My goal isn't to show tiles in a map, rather I want to automatically calculate some details about a user-selected drainage corridor (stretches people want to canoe/float, to be specific). For example, once the user sets an area (+/- 10 miles ^2) and choses their endpoints, I'd like to derive information like drop in elevation between endpoints, overall slope of the run, and graph of the longitudinal profile for the reach would be a nice start. ..my thinking is, maybe I can implement difficulty metrics.
Ideal data traits:
- 30-meter pixels,
- png or tiff, tiles to mosaic or a custom BBox area is fine
- source offers full coverage of the US (at least the 48 contiguous)
- actual elevation values (i.e. I'm not looking for hillshades or textures.)
Example bounding area:
Alternatively, any approach conducive to auto-download of DEM tiles or clips based on a fixed grid or path/row combination would work, so long as there is either a preexisting grid to work with, or enough theory to pre-generate a grid. Of course, key to this is access to a repository of data that allows direct url or ftp access.
I'm very curious to see what people think. Thanks so much for any help or insights!
Edits and Followup:
USGS published a Landsat Path/Row shapefile ("ascending" means nighttime, and "descending" means daytime), this could be helpful...Landsat does not include DEM, I was confusing that with the panchrome band.. ::shakes head:: DEM Explorer may provide a solution. I conducted an area download while running Fiddler; the data requests is performed via HTTP Post, and it responded with some cool feedback. It's definitely readable and parseable, only I'm not sure (yet) if any cookies or session stuff would prevent me from automating it. Time will tell.Shucks.. it seems to require sessions.
http://geobrain.laits.gmu.edu/wcs4dem.htm It seems the makers of DEM Explorer (above) provide a WCS gateway that serves geotiff DEM clips for BBox regions. Thanks to @BradHards for finding this. Here's an example call to the WCS service against the example bounding region I noted above: