DEM-tools

Background

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

Installation

To install the DEM-tools, type the following (you may need superuser priveleges):

npm install -g demtools

The dem2png and dem2dat will now be available on the command line.

Usage

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

The 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 and 255,255,255, where 0,0,0 represents the lowest elevation in the map, and 255,255,255 the highest.

dem2dat

The 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.

Both dem2png and 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.

Author

The author of DEM-tools is Werner Vesterås [e-mail]