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\" =========================================================================
\" utm2ll.1 - The manual page for the utm2ll program.
\" Copyright (c) 2000 Fred M. Erickson
\"
\" This program is free software; you can redistribute it and/or modify
\" it under the terms of the GNU General Public License as published by
\" the Free Software Foundation; either version 2, or (at your option)
\" any later version.
\"
\" This program is distributed in the hope that it will be useful,
\" but WITHOUT ANY WARRANTY; without even the implied warranty of
\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
\" GNU General Public License for more details.
\"
\" You should have received a copy of the GNU General Public License
\" along with this program; if not, write to the Free Software
\" Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
\" =========================================================================
.TH UTM2LL 1 \" -*- nroff -*-
.SH NAME
utm2ll \- Convert UTM coordinates to latitude/longitude geographical coordinates
.SH SYNOPSIS
.B utm2ll
[-L] | [utm_x utm_y zone [nad27 | nad83 | wgs84]]
.SH DESCRIPTION
This program uses Redfearn's formulas to convert a given set of Universal
Transverse Mercator (UTM) coordinates into the equivalent latitude and longitude
geographical coordinates. (This operation is often referred to
as inverse projection, since it projects a previously-projected flat surface
back onto the curved surface from whence it originally came.)
The inputs are the UTM "x" (also known as easting) value,
the UTM "y" (also known as northing) value, and the utm zone.
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.
For points in the southern hemisphere, make the zone number negative.
.PP
Warning: Not all of the possible triples of utm_x, utm_y, and zone
values represent correct UTM coordinates. The program will generally still
produce latitude/longitude coordinates, even for incorrect inputs.
You can check that your original inputs were correct by using
.I ll2utm
to convert the latitude/longitude coordinates back into UTM coordinates.
.PP
The output takes the form of a single line, containing the latitude
and longitude, separated by white space.
The values are in decimal degrees; with latitudes south of the
equator being negative, and longitudes west of the prime meridian being negative.
.PP
If you provide just the "-L" option, the program will print some license
information and exit.
.PP
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).
.PP
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.
.SH SEE ALSO
The
.I ll2utm(1)
command provides the inverse conversion.
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