Here's one I found
1. Go to
http://seamless.usgs.gov/
2. Click on one of the viewers (US viewer for me).
3. Wait for interface to load and map to display (java script
security options for your browser must be set to allow image
changes).
4. On the right hand data selection options for Download Layers,select the data SRTM,NED etc, and clear all others. Of course, do play with the various data layer options. You may find them important and/or useful. Same for the Download Layers. You can get some useful info delivered to you as well.
5. Use the magnifier + tool to drag a zoom in box around the
geographical region of interest.
6.Use the Download rectangular selection tool to click and drag out a selection area (I settled on roughly 40 to 50 miles on aside as gaged by the legend scale). When the mouse button is released, an order request window appears.
7. Close the window if the size of the area results in a product that's over 100 MB as such can't be downloaded (mine were around 30 to 50 megs) and drag out a smaller selection box.
8. In the order request window, click on the 'modify data request'button and change the delivery format from the default ArcGrid to BIL, then click on Save Changes button (bottom of screen).
9. Back at the request screen, notice the much smaller estimated package size. Click on the download link and wait for the raster extraction and archive processing to work. When done, a Save As dialog box appears. Save the file where best for you on your hard drive. (the zip file makes the file size even smaller than the estimate).
10. Open the archive and extract the contents to the folder where resample.exe is located.
11. Load the BIL data into Microdem, Global Mapper, Grass, or other similar dem viewer/editor (you really only need just the files named with a number... *.bil, *.hdr, *.prj, *.blw)
12. Get the lat/lon coords for each corner and the number of
columns and rows (some of this will be in the HDR file contained in the archive). Some viewers will even show you the degrees per pixel value, otherwise compute them by (N lat - S lat) / rows and (W lon - E lon) / columns.
13. Write an INF file for Resample per SDK using the above coords and values. The Source file will be the BIL from the archive.The Destination can be whatever you want the BGL file to be named.
14. Run the INF thru Resample and toss the resulting BGL into yourFS Addon Scenerey/scenery folder.
15. That's it.
The hard part is writing the INF file and maybe getting the EXACT decimal coords and pixel aspect ratios, but I've noticed that my rather random drag and draw selection boxes all produced products that the USGS processed such that the degrees/pixel values were both 2.7777777778e-4. Oh, SRTM 30m is best resampled at LOD 10 (38.2m). LOD 11 (19.1m) just makes for a larger file without hardly any noticable mesh detail improvement because nearly all the fine detail is visually masked by the terrain textures and scenery objects anyway).
There is one big problem with this direct DEM to BGL approach...SRTM data has holes/missing data typically around water (radar must have issues with it). These will leave craters and pits as the lack of data is considered sea level. The only recourse is to touch up the data in your DEM editor and export or save in 2 byte signed binary format (Global Mapper can save BIL in various flavors. 2 byte signed integer is the correct one, not BIL or BSQ).
Hope this mini tutorial is helpful.
