ll2utm(1) Convert latitude/longitude geographical coordinates to UTM coordinates


ll2utm [-L] | [latitude longitude [nad27 | nad83 | wgs84]]


This program uses Redfearn's formulas to convert a given latitude and longitude into the equivalent Universal Transverse Mercator (UTM) coordinates. (This operation is often referred to as projection, since it projects a curved surface onto a flat plane.) The input latitude and longitude must be in decimal degrees. Latitudes south of the equator are negative, and longitudes west of the prime meridian are negative. UTM is intended for use in the latitude range from 80S to 84N. The program will accept input outside of this range, but will print a warning message.

The output takes the form of a single line, containing the UTM "x" value, the UTM "y" value, and the UTM zone, separated by white space. The "x" value includes the normal 500,000 false easting. The "y" value includes the normal 10,000,000 false northing, if the point is in the southern hemisphere. Points in the southern hemisphere are flagged by making the zone number negative.

If you provide just the "-L" option, the program will print some license information and exit.

Projections, and inverse projections, depend on defining an ellipsoid that approximates the shape of the earth (the reference ellipsoid) and defining reference coordinates (the datum) that allow measurements to be made. Different choices of the ellipsoid and datum can yield projections that differ by tens of meters. There are a wide variety of choices, due to both the historical progression of measurement technology, and the desire to maximize accuracy over a given region (such as North America, or one of the United States).

This program defaults to the North American Datum of 1927 (NAD-27) with the Clarke Ellipsoid of 1866, since these appear to be appropriate for much of the freely-available data. The data are apparently in the process of being converted to the Geodetic Reference System 1980 (GRS-80) ellipsoid and NAD-83. If you come across such data, you can specify "nad83" on the command line. The GTOPO30 data use the World Geodetic System 1984 (WGS-84) ellipsoid, which can be invoked by specifying "wgs84" on the command line.