NAME¶
ll2utm - Convert latitude/longitude geographical coordinates to UTM coordinates
SYNOPSIS¶
ll2utm [-L] | [latitude longitude [nad27 | nad83 | wgs84]]
DESCRIPTION¶
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.
SEE ALSO¶
The
utm2ll(1) command provides the inverse conversion.
