The USGS Digital Elevation Model (DEM) data files are digital representations of cartographic information in a raster form. A DEM file consist of a sampled array of elevations for a number of ground positions at regularly spaced intervals.
DEM-tools consists of the following command line utilities:
dem2png- a utility for converting a DEM file to a PNG file
dem2dat- a utility for converting a DEM file to a DAT file
To install the DEM-tools, type the following (you may need superuser priveleges):
npm install -g demtools
dem2dat will now be available on the command line.
The DEM file format is not very efficient to work with, due to huge files. Converting the DEM files to more convenient formats makes very much sense. DEM-tools let you convert a DEM file into a PNG file, or a binary file.
dem2png utility takes a DEM file as its input, and creates a PNG file, where elevation in represented as a grayscale value between
0,0,0 represents the lowest elevation in the map, and
255,255,255 the highest.
dem2dat utility also takes a DEM file as its input, but creates a binary file, where each (unsigned) byte represents an elevation sample.
0x00 represents the lowest elevation in the map, and
0xff the highest.
dem2dat will also output a metadata file. An example of the contents of a metadata file:
z: 33 w: 5041 h: 5041 nw: 199800,6700200 ne: 250200,6700200 se: 250200,6649800 sw: 199800,6649800 min_ele: 13 max_ele: 1061 res_ew: 10 res_ew: 10 res_ele: 0.1
The metadata file contains the following information derived from the DEM file:
- The UTM zone.
- The width and height in samples.
- The corner coordinates (in UTM, as easting/northing pairs).
- Minimum and maximum elevations.
- The spatial resolutions.
The author of DEM-tools is Werner Vesterås email@example.com