ZoneConv is a command-line utility designed to transform the coordinates and elevations provided in a standard USGS 7.5-minute DEM into the coordinates and elevations as measured in the adjacent UTM zone. A user provides the name of the DEM file to be converted and the name of the output (transformed) DEM file to be created.
ZoneConv is supplied as part of Geophysical Software's Terrain Correction Package. Those interested in a separate license should contact Geophysical Software for pricing (info@geopotential.com, or 505-216-1611).
ZoneConv can only be used on 7.5-minute DEMs produced to meet the format standard published by the U. S. Geological Survey. In particular, the DEMs to be converted must provide planimetric coordinates as UTM coordinates, rather than State Plane coordinates. Although the USGS standard permits State Plane coordinates to be used, no DEMs produced by the USGS use State Plane coordinates to the author's knowledge.
ZoneConv operates by reading the original DEM data, which forms a grid with a somewhat ragged boundary, then calculating the UTM coordinates (in the new zone) of the elevation samples of the DEM in the new UTM zone. These coordinates are then transformed to geographic coordinates (that is, longitudes and latitudes), then to coordinates measured in the original UTM zone of the DEM. Elevations are then interpolated at these locations using bilinear interpolation from the original DEM elevations, which are provided as a grid. Note that only interpolation is used: any elevation samples in the "new" UTM zone that fall outside of the original DEM grid are not extrapolated.
Because of the nature in which the USGS 7.5-min DEMs are produced, when changing zones, there will be slivers of elevation data in the new DEM that cannot be calculated from elevations in the original DEM without performing some sort of extrapolation (rather than interpolation). The values of such elevation samples are set to -32767, which is the value used by USGS to indicate "no data" or a void in the DEM.
Note that such void values are not used by the terrain correction routine, InnerTC (that is, such values are ignored).
ZoneConv is a simple command-line utility. The syntax is
ZoneConv InputDEMFile OutputDEMFile
where InputDEMFile is the DEM file containing the elevation data to be converted, and OutputDEMFile is the name of the file that will contain the new DEM (that is, in the adjacent UTM zone). Note that the names of the files InputDEMFile and OutputDEMFile can coincide. This is NOT RECOMMENDED, however, as the original DEM data will be lost.
Note that the original DEM may be provided as a compressed file, if compressed using gzip. In such cases, the file name extension should be ".gz". The output file is never written as a compressed file, although a used can always compress it later.
Typing
ZonvConv -L
will display the licensee of the routine, as well as the version and build date.
A listing that shows the parameters of the original DEM, as well as a summary of the profiles written to the new DEM, is written to a file named ZoneConv.lst.