USGS Mapping Software: DLGV32
A few years ago, after I bought my GPS, I got into map making and map software. There’s a lot of data available for free from the USGS. They don’t make it easy to find, but it’s out there if you look hard enough.
One of the free viewers of USGS data that was available when I was doing this years ago was DLGV32. DLGV32 was originally written by a USGS employee in the mid-90s. This employee then left the USGS and started selling DLGV32 “Pro” himself. You can find his commercial version of the program online for $219 at GlobalMapper.com.
Since I was last making maps, something must have happened with DLGV32. The “Pro” version is now available from the USGS (link above), along with the source code. I’ve since become interested in mapping again so I thought I’d try out the source code.
Impressions of the source code:
- The DLGV32Pro source is dated March 2005 but is built using MSVC++ 6. ???
- Here’s something I’ve never seen before: debug symbols were explicitly turned off on key files. It took me a while to figure this out.
- The shipping source available on their website won’t compile, it contains trivial typos that prevent it from compiling.
It’s as if they want to discourage you from compiling and exploring the source code. Hmm.. could that be because there’s a former USGS employee trying to sell a commercial version of the same program??
There are libraries available to parse USGS map data, like data in the STDS format. One of these is the stds++ library but it’s built to compile on the MSVC++ 6 version of STL, which is a mess. I don’t feel like bringing it up to VS.NET2003.
The USGS Seamless Data Distribution website is a good place to get vector data, like roads, railroads in DLG and SDTS formats.
MapMart.com has 7.5 minute super high resolution elevation maps available in SDTS format.
The EROS Data Center keeps on their ftp site 1:250,000 scale digital elevation map (DEM) files. 7.5 Minute data is also available, but I can’t find a user-friendly index so you have to guess from the file names. DEM is by far the easiest file format to deal with. I’ve managed to figure out the format myself, but I’m still looking for a good tutorial on how you’re officially supposed to deal with the file format. The official specification is amazing verbose while still lacking the essentials necessary to get started parsing the format. A grammar would be a nice start.