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<title>MAPPROJECT</title>
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<h1 align=center>MAPPROJECT</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#OPTIONS">OPTIONS</a><br>
<a href="#ASCII FORMAT PRECISION">ASCII FORMAT PRECISION</a><br>
<a href="#EXAMPLES">EXAMPLES</a><br>
<a href="#RESTRICTIONS">RESTRICTIONS</a><br>
<a href="#ELLIPSOIDS AND SPHEROIDS">ELLIPSOIDS AND SPHEROIDS</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#REFERENCES">REFERENCES</a><br>
<hr>
<a name="NAME"></a>
<h2>NAME</h2>
<p style="margin-left:11%; margin-top: 1em">mapproject
− Forward and Inverse map transformation of 2-D
coordinates</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>mapproject</b>
<i>infiles</i> <b>−J</b><i>parameters</i>
<b>−R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>]
[
<b>−Ab</b>|<b>B</b>|<b>f</b>|<b>F</b>[<i>lon0</i>/<i>lat0</i>]
] [ <b>−C</b>[<i>dx</i>/<i>dy</i>] ] [
<b>−Dc</b>|<b>i</b>|<b>m</b>|<b>p</b> ] [
<b>−E</b>[<i>datum</i>] ] [
<b>−F</b>[<b>k</b>|<b>m</b>|<b>n</b>|<b>i</b>|<b>c</b>|<b>p</b>]
] [
<b>−G</b>[<i>x0</i>/<i>y0</i>][<b>+</b>|<b>-</b>][/<i>unit</i>]
] [ <b>−H</b>[<b>i</b>][<i>nrec</i>] ] [
<b>−I</b> ] [
<b>−L</b><i>line.xy</i>[/<i>unit</i>][<b>+</b>] ] [
<b>−Q</b>[<b>d</b>|<b>e</b> ] [ <b>−S</b> ] [
<b>−T</b>[<b>h</b>]<i>from</i>[/<i>to</i>] ] [
<b>−V</b> ] [ <b>−:</b>[<b>i</b>|<b>o</b>] ] [
<b>−b</b>[<b>i</b>|<b>o</b>][<b>s</b>|<b>S</b>|<b>d</b>|<b>D</b>[<i>ncol</i>]|<b>c</b>[<i>var1</i><b>/</b><i>...</i>]]
] [ <b>−f</b>[<b>i</b>|<b>o</b>]<i>colinfo</i> ] [
<b>−g</b>[<b>a</b>]<b>x</b>|<b>y</b>|<b>d</b>|<b>X</b>|<b>Y</b>|<b>D</b>|[<i>col</i>]<b>z</b>[+|-]<i>gap</i>[<b>u</b>]
] [ <b>−m</b>[<b>i</b>|<b>o</b>][<i>flag</i>] ]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>mapproject</b>
reads (longitude, latitude) positions from <i>infiles</i>
[or standard input] and computes (x,y) coordinates using the
specified map projection and scales. Optionally, it can read
(x,y) positions and compute (longitude, latitude) values
doing the inverse transformation. This can be used to
transform linear (x,y) points obtained by digitizing a map
of known projection to geographical coordinates. May also
calculate distances along track, to a fixed point, or
closest approach to a line. Finally, can be used to perform
various datum conversions. Additional data fields are
permitted after the first 2 columns which must have
(longitude,latitude) or (x,y). See option <b>−:</b> on
how to read (latitude,longitude) files. <i><br>
infiles</i></p>
<p style="margin-left:22%;">Data file(s) to be transformed.
If not given, standard input is read.</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−J</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects the map
projection. The following character determines the
projection. If the character is upper case then the
argument(s) supplied as scale(s) is interpreted to be the
map width (or axis lengths), else the scale argument(s) is
the map scale (see its definition for each projection). UNIT
is cm, inch, or m, depending on the <b><A HREF="gmtdefaults.html#MEASURE_UNIT">MEASURE_UNIT</A></b>
setting in .gmtdefaults4, but this can be overridden on the
command line by appending <b>c</b>, <b>i</b>, or <b>m</b> to
the <i>scale</i> or <i>width</i> values. Append <b>h</b>,
<b>+</b>, or <b>-</b> to the given <i>width</i> if you
instead want to set map height, the maximum dimension, or
the minimum dimension, respectively [Default is <b>w</b> for
width].</p> </td>
</table>
<p style="margin-left:22%;">In case the central meridian is
an optional parameter and it is being omitted, then the
center of the longitude range given by the <b>−R</b>
option is used. The default standard parallel is the
equator. <br>
The ellipsoid used in the map projections is user-definable
by editing the .gmtdefaults4 file in your home directory. 73
commonly used ellipsoids and spheroids are currently
supported, and users may also specify their own custum
ellipsoid parameters [Default is WGS-84]. Several GMT
parameters can affect the projection: <b><A HREF="gmtdefaults.html#ELLIPSOID">ELLIPSOID</A></b>,
<b><A HREF="gmtdefaults.html#INTERPOLANT">INTERPOLANT</A></b>, <b><A HREF="gmtdefaults.html#MAP_SCALE_FACTOR">MAP_SCALE_FACTOR</A></b>, and
<b><A HREF="gmtdefaults.html#MEASURE_UNIT">MEASURE_UNIT</A></b>; see the <b><A HREF="gmtdefaults.html">gmtdefaults</A></b> man page for
details. <br>
Choose one of the following projections (The <b>E</b> or
<b>C</b> after projection names stands for Equal-Area and
Conformal, respectively):</p>
<p style="margin-left:22%; margin-top: 1em"><b>CYLINDRICAL
PROJECTIONS: <br>
−Jc</b><i>lon0/lat0/scale</i> or
<b>−JC</b><i>lon0/lat0/width</i> (Cassini).</p>
<p style="margin-left:32%;">Give projection center
<i>lon0/lat0</i> and <i>scale</i> (<b>1:</b><i>xxxx</i> or
UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jcyl_stere</b>/[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
or <b><br>
−JCyl_stere</b>/[<i>lon0/</i>[<i>lat0/</i>]]<i>width</i>
(Cylindrical Stereographic).</p>
<p style="margin-left:32%;">Give central meridian
<i>lon0</i> (optional), standard parallel <i>lat0</i>
(optional), and <i>scale</i> along parallel
(<b>1:</b><i>xxxx</i> or UNIT/degree). The standard parallel
is typically one of these (but can be any value):</p>
<p style="margin-left:43%;">66.159467 - Miller’s
modified Gall <br>
55 - Kamenetskiy’s First <br>
45 - Gall’s Stereographic <br>
30 - Bolshoi Sovietskii Atlas Mira or Kamenetskiy’s
Second <br>
0 - Braun’s Cylindrical</p>
<p style="margin-left:22%;"><b>−Jj</b>[<i>lon0/</i>]<i>scale</i>
or <b>−JJ</b>[<i>lon0/</i>]<i>width</i> (Miller
Cylindrical <br>
Projection).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional) and <i>scale</i>
(<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jm</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
or
<b>−JM</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>width</i></p>
<p style="margin-left:32%;">Give central meridian
<i>lon0</i> (optional), standard parallel <i>lat0</i>
(optional), and <i>scale</i> along parallel
(<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jo</b><i>parameters</i>
(Oblique Mercator <b>[C]</b>).</p>
<p style="margin-left:32%;">Typically used with
<b>−R</b><...><b>r</b>, otherwise region is in
oblique coordinates. Specify one of: <b><br>
−Jo</b>[<b>a</b>]<i>lon0/lat0/azimuth/scale</i> or
<b><br>
−JO</b>[<b>a</b>]<i>lon0/lat0/azimuth/width</i></p>
<p style="margin-left:43%;">Set projection center
<i>lon0/lat0</i>, <i>azimuth</i> of oblique equator, and
<i>scale</i>.</p>
<p style="margin-left:32%;"><b>−Jo</b>[<b>b</b>]<i>lon0/lat0/lon1/lat1/scale</i>
or <b><br>
−JO</b>[<b>b</b>]<i>lon0/lat0/lon1/lat1/scale</i></p>
<p style="margin-left:43%;">Set projection center
<i>lon0/lat0</i>, another point on the oblique equator
<i>lon1/lat1</i>, and <i>scale</i>.</p>
<p style="margin-left:32%;"><b>−Joc</b><i>lon0/lat0/lonp/latp/scale</i>
or <b><br>
−JOc</b><i>lon0/lat0/lonp/latp/scale</i></p>
<p style="margin-left:43%;">Set projection center
<i>lon0/lat0</i>, pole of oblique projection
<i>lonp/latp</i>, and <i>scale</i>.</p>
<p style="margin-left:32%; margin-top: 1em">Give
<i>scale</i> along oblique equator (<b>1:</b><i>xxxx</i> or
UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jq</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
or <b>−JQ</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>width</i>
(Cylindrical <br>
Equidistant).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional), standard parallel <i>lat0</i>
(optional), and <i>scale</i> (<b>1:</b><i>xxxx</i> or
UNIT/degree). The standard parallel is typically one of
these (but can be any value):</p>
<p style="margin-left:43%;">61.7 - Grafarend and Niermann,
minimum linear distortion <br>
50.5 - Ronald Miller Equirectangular <br>
43.5 - Ronald Miller, minimum continental distortion <br>
42 - Grafarend and Niermann <br>
37.5 - Ronald Miller, minimum overall distortion <br>
0 - Plate Carree, Simple Cylindrical, Plain/Plane Chart</p>
<p style="margin-left:22%;"><b>−Jt</b><i>lon0/</i>[<i>lat0/</i>]<i>scale</i>
or
<b>−JT</b><i>lon0/</i>[<i>lat0/</i>]<i>width</i></p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i>, central parallel <i>lat0</i> (optional), and
<i>scale</i> (<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Ju</b><i>zone/scale</i>
or <b>−JU</b><i>zone/width</i> (UTM - Universal
Transverse <br>
Mercator <b>[C]</b>).</p>
<p style="margin-left:32%;">Give the UTM zone
(A,B,1-60[C-X],Y,Z)) and <i>scale</i> (<b>1:</b><i>xxxx</i>
or UNIT/degree). <br>
Zones: If C-X not given, prepend - or + to enforce southern
or northern hemisphere conventions [northern if south >
0].</p>
<p style="margin-left:22%;"><b>−Jy</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
or <b>−JY</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>width</i>
(Cylindrical <br>
Equal-Area <b>[E]</b>).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional), standard parallel <i>lat0</i>
(optional), and <i>scale</i> (<b>1:</b><i>xxxx</i> or
UNIT/degree). The standard parallel is typically one of
these (but can be any value):</p>
<p style="margin-left:43%;">50 - Balthasart <br>
45 - Gall-Peters <br>
37.0666 - Caster <br>
37.4 - Trystan Edwards <br>
37.5 - Hobo-Dyer <br>
30 - Behrman <br>
0 - Lambert (default)</p>
<p style="margin-left:22%; margin-top: 1em"><b>CONIC
PROJECTIONS: <br>
−Jb</b><i>lon0/lat0/lat1/lat2/scale</i> or
<b>−JB</b><i>lon0/lat0/lat1/lat2/width</i> <br>
(Albers <b>[E]</b>).</p>
<p style="margin-left:32%;">Give projection center
<i>lon0/lat0</i>, two standard parallels <i>lat1/lat2</i>,
and <i>scale</i> (<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jd</b><i>lon0/lat0/lat1/lat2/scale</i>
or <b>−JD</b><i>lon0/lat0/lat1/lat2/width</i> <br>
(Conic Equidistant)</p>
<p style="margin-left:32%;">Give projection center
<i>lon0/lat0</i>, two standard parallels <i>lat1/lat2</i>,
and <i>scale</i> (<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jl</b><i>lon0/lat0/lat1/lat2/scale</i>
or <b>−JL</b><i>lon0/lat0/lat1/lat2/width</i> <br>
(Lambert <b>[C]</b>)</p>
<p style="margin-left:32%;">Give origin <i>lon0/lat0</i>,
two standard parallels <i>lat1/lat2</i>, and <i>scale</i>
along these (<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jpoly</b>/[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
or
<b>−JPoly</b>/[<i>lon0/</i>[<i>lat0/</i>]]<i>width</i>
<br>
((American) Polyconic).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional), reference parallel <i>lat0</i>
(optional, default = equator), and <i>scale</i> along
central meridian (<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%; margin-top: 1em"><b>AZIMUTHAL
PROJECTIONS:</b></p>
<p style="margin-left:22%; margin-top: 1em">Except for
polar aspects, <b>−R</b> w/e/s/n will be reset to
<b>−Rg</b>. Use <b>−R</b><...><b>r</b> for
smaller regions. <b><br>
−Ja</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
or
<b>−JA</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/width</i>
<br>
(Lambert <b>[E]</b>).</p>
<p style="margin-left:32%;"><i>lon0/lat0</i> specifies the
projection center. <i>horizon</i> specifies the max distance
from projection center (in degrees, <= 180, default 90).
Give <i>scale</i> as <b>1:</b><i>xxxx</i> or
<i>radius/lat</i>, where <i>radius</i> is distance in UNIT
from origin to the oblique latitude <i>lat</i>.</p>
<p style="margin-left:22%;"><b>−Je</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
or
<b>−JE</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/width</i>
<br>
(Azimuthal Equidistant).</p>
<p style="margin-left:32%;"><i>lon0/lat0</i> specifies the
projection center. <i>horizon</i> specifies the max distance
from projection center (in degrees, <= 180, default 180).
Give <i>scale</i> as <b>1:</b><i>xxxx</i> or
<i>radius/lat</i>, where <i>radius</i> is distance in UNIT
from origin to the oblique latitude <i>lat</i>.</p>
<p style="margin-left:22%;"><b>−Jf</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
or
<b>−JF</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/width</i>
<br>
(Gnomonic).</p>
<p style="margin-left:32%;"><i>lon0/lat0</i> specifies the
projection center. <i>horizon</i> specifies the max distance
from projection center (in degrees, < 90, default 60).
Give <i>scale</i> as <b>1:</b><i>xxxx</i> or
<i>radius/lat</i>, where <i>radius</i> is distance in UNIT
from origin to the oblique latitude <i>lat</i>.</p>
<p style="margin-left:22%;"><b>−Jg</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
or
<b>−JG</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/width</i>
<br>
(Orthographic).</p>
<p style="margin-left:32%;"><i>lon0/lat0</i> specifies the
projection center. <i>horizon</i> specifies the max distance
from projection center (in degrees, <= 90, default 90).
Give <i>scale</i> as <b>1:</b><i>xxxx</i> or
<i>radius/lat</i>, where <i>radius</i> is distance in UNIT
from origin to the oblique latitude <i>lat</i>.</p>
<p style="margin-left:22%;"><b>−Jg</b><i>lon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale</i>
or <b><br>
−JG</b><i>lon0/lat0/altitude/azimuth/tilt/twist/Width/Height/width</i>
<br>
(General Perspective).</p>
<p style="margin-left:32%;"><i>lon0/lat0</i> specifies the
projection center. <i>altitude</i> is the height (in km) of
the viewpoint above local sea level. If <i>altitude</i> is
less than 10, then it is the distance from the center of the
earth to the viewpoint in earth radii. If <i>altitude</i>
has a suffix <b>r</b> then it is the radius from the center
of the earth in kilometers. <i>azimuth</i> is measured to
the east of north of view. <i>tilt</i> is the upward tilt of
the plane of projection. If <i>tilt</i> is negative, then
the viewpoint is centered on the horizon. Further, specify
the clockwise <i>twist</i>, <i>Width</i>, and <i>Height</i>
of the viewpoint in degrees. Give <i>scale</i> as
<b>1:</b><i>xxxx</i> or <i>radius/lat</i>, where
<i>radius</i> is distance in UNIT from origin to the oblique
latitude <i>lat</i>.</p>
<p style="margin-left:22%;"><b>−Js</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
or
<b>−JS</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/width</i>
<br>
(General Stereographic <b>[C]</b>).</p>
<p style="margin-left:32%;"><i>lon0/lat0</i> specifies the
projection center. <i>horizon</i> specifies the max distance
from projection center (in degrees, < 180, default 90).
Give <i>scale</i> as <b>1:</b><i>xxxx</i> (true at pole) or
<i>lat</i>/<b>1:</b><i>xxxx</i> (true at standard parallel
<i>lat</i>) or <i>radius/lat</i> (<i>radius</i> in UNIT from
origin to the oblique latitude <i>lat</i>). Note if
<b>1:</b><i>xxxx</i> is used then to specify <i>horizon</i>
you must also specify the <i>lat</i> as +-90 to avoid
ambiguity.</p>
<p style="margin-left:22%; margin-top: 1em"><b>MISCELLANEOUS
PROJECTIONS: <br>
−Jh</b>[<i>lon0/</i>]<i>scale</i> or
<b>−JH</b>[<i>lon0/</i>]<i>width</i> (Hammer
<b>[E]</b>).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional) and <i>scale</i> along equator
(<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Ji</b>[<i>lon0/</i>]<i>scale</i>
or <b>−JI</b>[<i>lon0/</i>]<i>width</i> (Sinusoidal
<b>[E]</b>).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional) and <i>scale</i> along equator
(<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jkf</b>[<i>lon0/</i>]<i>scale</i>
or <b>−JKf</b>[<i>lon0/</i>]<i>width</i> (Eckert IV)
<b>[E]</b>).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional) and <i>scale</i> along equator
(<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jk</b>[<b>s</b>][<i>lon0/</i>]<i>scale</i>
or <b>−JK</b>[<b>s</b>][<i>lon0/</i>]<i>width</i>
(Eckert VI) <b>[E]</b>).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional) and <i>scale</i> along equator
(<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jn</b>[<i>lon0/</i>]<i>scale</i>
or <b>−JN</b>[<i>lon0/</i>]<i>width</i>
(Robinson).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional) and <i>scale</i> along equator
(<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jr</b>[<i>lon0/</i>]<i>scale</i>
<b>−JR</b>[<i>lon0/</i>]<i>width</i> (Winkel
Tripel).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional) and <i>scale</i> along equator
(<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jv</b>[<i>lon0/</i>]<i>scale</i>
or <b>−JV</b>[<i>lon0/</i>]<i>width</i> (Van der
Grinten).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional) and <i>scale</i> along equator
(<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%;"><b>−Jw</b>[<i>lon0/</i>]<i>scale</i>
or <b>−JW</b>[<i>lon0/</i>]<i>width</i> (Mollweide
<b>[E]</b>).</p>
<p style="margin-left:32%;">Give the central meridian
<i>lon0</i> (optional) and <i>scale</i> along equator
(<b>1:</b><i>xxxx</i> or UNIT/degree).</p>
<p style="margin-left:22%; margin-top: 1em"><b>NON-GEOGRAPHICAL
PROJECTIONS: <br>
−Jp</b>[<b>a</b>]<i>scale</i>[<i>/origin</i>][<b>r</b>|<b>z</b>]
or
<b>−JP</b>[<b>a</b>]<i>width</i>[<i>/origin</i>][<b>r</b>|<b>z</b>]
(Polar <br>
coordinates (theta,r))</p>
<p style="margin-left:32%;">Optionally insert <b>a</b>
after <b>−Jp</b> [ or <b>−JP</b>] for azimuths
CW from North instead of directions CCW from East [Default].
Optionally append /<i>origin</i> in degrees to indicate an
angular offset [0]). Finally, append <b>r</b> if r is
elevations in degrees (requires s >= 0 and n <= 90) or
<b>z</b> if you want to annotate depth rather than radius
[Default]. Give <i>scale</i> in UNIT/r-unit.</p>
<p style="margin-left:22%;"><b>−Jx</b><i>x-scale</i>[<i>/y-scale</i>]
or <b>−JX</b><i>width</i>[<i>/height</i>] (Linear,
log, and <br>
power scaling)</p>
<p style="margin-left:32%;">Give <i>x-scale</i>
(<b>1:</b><i>xxxx</i> or UNIT/x-unit) and/or <i>y-scale</i>
(<b>1:</b><i>xxxx</i> or UNIT/y-unit); or specify
<i>width</i> and/or <i>height</i> in UNIT.
<i>y-scale</i>=<i>x-scale</i> if not specified separately
and using <b>1:</b><i>xxxx</i> implies that x-unit and
y-unit are in meters. Use negative scale(s) to reverse the
direction of an axis (e.g., to have y be positive down). Set
<i>height</i> or <i>width</i> to 0 to have it recomputed
based on the implied scale of the other axis. Optionally,
append to <i>x-scale</i>, <i>y-scale</i>, <i>width</i> or
<i>height</i> one of the following:</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="32%"></td>
<td width="10%">
<p style="margin-top: 1em" valign="top"><b>d</b></p></td>
<td width="1%"></td>
<td width="57%">
<p style="margin-top: 1em" valign="top">Data are
geographical coordinates (in degrees).</p></td>
<tr valign="top" align="left">
<td width="32%"></td>
<td width="10%">
<p style="margin-top: 1em" valign="top"><b>l</b></p></td>
<td width="1%"></td>
<td width="57%">
<p style="margin-top: 1em" valign="top">Take log10 of
values before scaling.</p></td>
<tr valign="top" align="left">
<td width="32%"></td>
<td width="10%">
<p style="margin-top: 1em" valign="top"><b>p</b><i>power</i></p> </td>
<td width="1%"></td>
<td width="57%">
<p style="margin-top: 1em" valign="top">Raise values to
<i>power</i> before scaling.</p></td>
<tr valign="top" align="left">
<td width="32%"></td>
<td width="10%">
<p style="margin-top: 1em" valign="top"><b>t</b></p></td>
<td width="1%"></td>
<td width="57%">
<p style="margin-top: 1em" valign="top">Input coordinates
are time relative to <b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b>.</p></td>
<tr valign="top" align="left">
<td width="32%"></td>
<td width="10%">
<p style="margin-top: 1em" valign="top"><b>T</b></p></td>
<td width="1%"></td>
<td width="57%">
<p style="margin-top: 1em" valign="top">Input coordinates
are absolute time.</p></td>
</table>
<p style="margin-left:32%; margin-top: 1em">Default axis
lengths (see <b><A HREF="gmtdefaults.html">gmtdefaults</A></b>) can be invoked using
<b>−JXh</b> (for landscape); <b>−JXv</b> (for
portrait) will swap the x- and y-axis lengths. The default
unit for this installation is either cm or inch, as defined
in the file share/gmt_setup.conf. However, you may change
this by editing your .gmtdefaults4 file(s).</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−R</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top"><i>xmin</i>,
<i>xmax</i>, <i>ymin</i>, and <i>ymax</i> specify the Region
of interest. For geographic regions, these limits correspond
to <i>west, east, south,</i> and <i>north</i> and you may
specify them in decimal degrees or in
[+-]dd:mm[:ss.xxx][W|E|S|N] format. Append <b>r</b> if lower
left and upper right map coordinates are given instead of
w/e/s/n. The two shorthands <b>−Rg</b> and
<b>−Rd</b> stand for global domain (0/360 and
-180/+180 in longitude respectively, with -90/+90 in
latitude). Alternatively, specify the name of an existing
grid file and the <b>−R</b> settings (and grid
spacing, if applicable) are copied from the grid. For
calendar time coordinates you may either give (a) relative
time (relative to the selected <b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b> and in the
selected <b><A HREF="gmtdefaults.html#TIME_UNIT">TIME_UNIT</A></b>; append <b>t</b> to
<b>−JX</b>|<b>x</b>), or (b) absolute time of the form
[<i>date</i>]<b>T</b>[<i>clock</i>] (append <b>T</b> to
<b>−JX</b>|<b>x</b>). At least one of <i>date</i> and
<i>clock</i> must be present; the <b>T</b> is always
required. The <i>date</i> string must be of the form
[-]yyyy[-mm[-dd]] (Gregorian calendar) or yyyy[-Www[-d]]
(ISO week calendar), while the <i>clock</i> string must be
of the form hh:mm:ss[.xxx]. The use of delimiters and their
type and positions must be exactly as indicated (however,
input, output and plot formats are customizable; see
<b><A HREF="gmtdefaults.html">gmtdefaults</A></b>). Special case for the UTM projection: If
<b>−C</b> is used and <b>−R</b> is not given
then the region is set to coincide with the given UTM zone
so as to preserve the full ellipsoidal solution (See
RESTRICTIONS for more information).</p></td>
</table>
<a name="OPTIONS"></a>
<h2>OPTIONS</h2>
<p style="margin-left:11%; margin-top: 1em">No space
between the option flag and the associated arguments.
<i><br>
infile(s)</i></p>
<p style="margin-left:22%;">input file(s) with 2 or more
columns. If no file(s) is given, <b>mapproject</b> will read
the standard input.</p>
<p style="margin-left:11%;"><b>−A</b>[<b>f</b>|<b>b</b>]</p>
<p style="margin-left:22%;"><b>−A</b> calculates the
(forward) azimuth from fixed point <i>lon/lat</i> to each
data point. Use <b>−Ab</b> to get back-azimuth from
data points to fixed point. Upper case <b>F</b> or <b>B</b>
will convert from geodetic to geocentric latitudes and
estimate azimuth of geodesics (assuming the current
ellipsoid is not a sphere). If no fixed point is given then
we compute the azimuth (or back-azimuth) from the previous
point.</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−C</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Set center of
projected coordinates to be at map projection center
[Default is lower left corner]. Optionally, add offsets in
the projected units to be added (or subtracted when
<b>−I</b> is set) to (from) the projected coordinates,
such as false eastings and northings for particular
projection zones [0/0]. The unit used for the offsets is the
plot distance unit in effect (see <b><A HREF="gmtdefaults.html#MEASURE_UNIT">MEASURE_UNIT</A></b>)
unless <b>−F</b> is used, in which case the offsets
are always in meters.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−D</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Temporarily
override <b><A HREF="gmtdefaults.html#MEASURE_UNIT">MEASURE_UNIT</A></b> and use <b>c</b> (cm), <b>i</b>
(inch), <b>m</b> (meter), or <b>p</b> (points) instead.
Cannot be used with <b>−F</b>.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−E</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Convert from
geodetic (lon, lat, height) to Earth Centered Earth Fixed
(ECEF) (x,y,z) coordinates (add <b>−I</b> for the
inverse conversion). Append datum ID (see <b>−Qd</b>)
or give <i>ellipsoid</i>:<i>dx,dy,dz</i> where
<i>ellipsoid</i> may be an ellipsoid ID (see
<b>−Qe</b>) or given as <i>a</i>[,<i>inv_f</i>], where
<i>a</i> is the semi-major axis and <i>inv_f</i> is the
inverse flattening (0 if omitted). If <i>datum</i> is - or
not given we assume WGS-84.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−F</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Force 1:1 scaling,
i.e., output (or input, see <b>−I</b>) data are in
actual projected meters. To specify other units, append
<b>k</b> (km), <b>m</b> (mile), <b>n</b> (nautical mile),
<b>i</b> (inch), <b>c</b> (cm), or <b>p</b> (points).
Without <b>−F</b>, the output (or input, see
<b>−I</b>) are in the units specified by
<b><A HREF="gmtdefaults.html#MEASURE_UNIT">MEASURE_UNIT</A></b> (but see <b>−D</b>).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−G</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Calculate distances
along track OR to the optional point set with
<b>−G</b><i>x0/y0</i>. Append IT(unit), the distance
unit; choose among <b>e</b> (m), <b>k</b> (km), <b>m</b>
(mile), <b>n</b> (nautical mile), <b>d</b> (spherical
degree), <b>c</b> (Cartesian distance using input
coordinates) or <b>C</b> (Cartesian distance using projected
coordinates). The last unit requires <b>−R</b> and
<b>−J</b> to be set. Upper case <b>E</b>, <b>K</b>,
<b>M</b>, <b>N</b>, or <b>D</b> will use exact methods for
geodesic distances (Rudoe’s method for distances in
length units and employing geocentric latitudes in degree
calculations, assuming the current ellipsoid is not
spherical). With no fixed point we calculate cumulate
distances along track. To obtain incremental distance
between successive points, use <b>−G-</b>. To specify
the 2nd point via two extra columns in the input file,
choose <b>−G+</b>.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−H</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Input file(s) has
header record(s). If used, the default number of header
records is <b><A HREF="gmtdefaults.html#N_HEADER_RECS">N_HEADER_RECS</A></b>. Use <b>−Hi</b> if
only input data should have header records [Default will
write out header records if the input data have them]. Blank
lines and lines starting with # are always skipped.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−I</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Do the Inverse
transformation, i.e., get (longitude,latitude) from (x,y)
data.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−L</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Determine the
shortest distance from the input data points to the line(s)
given in the ASCII multi-segment file <i>line.xy</i>. The
distance and the coordinates of the nearest point will be
appended to the output as three new columns. Append the
distance unit; choose among <b>e</b> (m), <b>k</b> (km),
<b>m</b> (mile), <b>n</b> (nautical mile), <b>d</b>
(spherical degree), <b>c</b> (Cartesian distance using input
coordinates) or <b>C</b> (Cartesian distance using projected
coordinates). The last unit requires <b>−R</b> and
<b>−J</b> to be set. A spherical approximation is used
for geographic data. Finally, append <b>+</b> to report the
line segment id and the fractional point number instead of
lon/lat of the nearest point.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Q</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">List all projection
parameters. To only list datums, use <b>−Qd</b>. To
only list ellipsoids, use <b>−Qe</b>.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−S</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Suppress points
that fall outside the region.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−T</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Coordinate
conversions between datums <i>from</i> and <i>to</i> using
the standard Molodensky transformation. Use <b>−Th</b>
if 3rd input column has height above ellipsoid [Default
assumes height = 0, i.e., on the ellipsoid]. Specify datums
using the datum ID (see <b>−Qd</b>) or give
<i>ellipsoid</i>:<i>dx,dy,dz</i> where <i>ellipsoid</i> may
be an ellipsoid ID (see <b>−Qe</b>) or given as
<i>a</i>[,<i>inv_f</i>], where <i>a</i> is the semi-major
axis and <i>inv_f</i> is the inverse flattening (0 if
omitted). If <i>datum</i> is - or not given we assume
WGS-84. <b>−T</b> may be used in conjunction with
<b>−R −J</b> to change the datum before
coordinate projection (add <b>−I</b> to apply the
datum conversion after the inverse projection). Make sure
that the <b><A HREF="gmtdefaults.html#ELLIPSOID">ELLIPSOID</A></b> setting is correct for your
case.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−V</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects verbose
mode, which will send progress reports to stderr [Default
runs "silently"].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−:</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Toggles between
(longitude,latitude) and (latitude,longitude) input and/or
output. [Default is (longitude,latitude)]. Append <b>i</b>
to select input only or <b>o</b> to select output only.
[Default affects both].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−bi</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects binary
input. Append <b>s</b> for single precision [Default is
<b>d</b> (double)]. Uppercase <b>S</b> or <b>D</b> will
force byte-swapping. Optionally, append <i>ncol</i>, the
number of columns in your binary input file if it exceeds
the columns needed by the program. Or append <b>c</b> if the
input file is netCDF. Optionally, append
<i>var1</i><b>/</b><i>var2</i><b>/</b><i>...</i> to specify
the variables to be read. [Default is 2 input columns].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−bo</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects binary
output. Append <b>s</b> for single precision [Default is
<b>d</b> (double)]. Uppercase <b>S</b> or <b>D</b> will
force byte-swapping. Optionally, append <i>ncol</i>, the
number of desired columns in your binary output file.
[Default is same as input].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−f</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Special formatting
of input and/or output columns (time or geographical data).
Specify <b>i</b> or <b>o</b> to make this apply only to
input or output [Default applies to both]. Give one or more
columns (or column ranges) separated by commas. Append
<b>T</b> (absolute calendar time), <b>t</b> (relative time
in chosen <b><A HREF="gmtdefaults.html#TIME_UNIT">TIME_UNIT</A></b> since <b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b>),
<b>x</b> (longitude), <b>y</b> (latitude), or <b>f</b>
(floating point) to each column or column range item.
Shorthand <b>−f</b>[<b>i</b>|<b>o</b>]<b>g</b> means
<b>−f</b>[<b>i</b>|<b>o</b>]0<b>x</b>,1<b>y</b>
(geographic coordinates).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−g</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Examine the spacing
between consecutive data points in order to impose breaks in
the line. Append <b>x</b>|<b>X</b> or <b>y</b>|<b>Y</b> to
define a gap when there is a large enough change in the x or
y coordinates, respectively, or <b>d</b>|<b>D</b> for
distance gaps; use upper case to calculate gaps from
projected coordinates. For gap-testing on other columns use
[<i>col</i>]<b>z</b>; if <i>col</i> is not prepended the it
defaults to 2 (i.e., 3rd column). Append [+|-]<i>gap</i> and
optionally a unit <b>u</b>. Regarding optional signs: -ve
means previous minus current column value must exceed
|<i>gap</i> to be a gap, +ve means current minus previous
column value must exceed <i>gap</i>, and no sign means the
absolute value of the difference must exceed <i>gap</i>. For
geographic data (<b>x</b>|<b>y</b>|<b>d</b>), the unit
<b>u</b> may be m<b>e</b>ter [Default], <b>k</b>ilometer,
<b>m</b>iles, or <b>n</b>autical miles. For projected data
(<b>X</b>|<b>Y</b>|<b>D</b>), choose from <b>i</b>nch,
<b>c</b>entimeter, <b>m</b>eter, or <b>p</b>oints [Default
unit set by MEASURE_UNIT]. Note: For
<b>x</b>|<b>y</b>|<b>z</b> with time data the unit is
instead controlled by TIME_UNIT. Repeat the option to
specify multiple criteria, of which any can be met to
produce a line break. Issue an additional <b>−ga</b>
to indicate that all criteria must be met instead.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−m</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Multiple segment
file(s). Segments are separated by a special record. For
ASCII files the first character must be <i>flag</i> [Default
is ’>’]. For binary files all fields must be
NaN and <b>−b</b> must set the number of output
columns explicitly. By default the <b>−m</b> setting
applies to both input and output. Use <b>−mi</b> and
<b>−mo</b> to give separate settings to input and
output.</p> </td>
</table>
<a name="ASCII FORMAT PRECISION"></a>
<h2>ASCII FORMAT PRECISION</h2>
<p style="margin-left:11%; margin-top: 1em">The ASCII
output formats of numerical data are controlled by
parameters in your .gmtdefaults4 file. Longitude and
latitude are formatted according to
<b><A HREF="gmtdefaults.html#OUTPUT_DEGREE_FORMAT">OUTPUT_DEGREE_FORMAT</A></b>, whereas other values are
formatted according to <b><A HREF="gmtdefaults.html#D_FORMAT">D_FORMAT</A></b>. Be aware that the
format in effect can lead to loss of precision in the
output, which can lead to various problems downstream. If
you find the output is not written with enough precision,
consider switching to binary output (<b>−bo</b> if
available) or specify more decimals using the
<b><A HREF="gmtdefaults.html#D_FORMAT">D_FORMAT</A></b> setting.</p>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
<p style="margin-left:11%; margin-top: 1em">To transform a
file with (longitude,latitude) into (x,y) positions in cm on
a Mercator grid for a given scale of 0.5 cm per degree,
run</p>
<p style="margin-left:11%; margin-top: 1em"><b>mapproject</b>
lonlatfile <b>−R</b> 20/50/12/25 <b>−Jm</b>
0.5<b>c</b> > xyfile</p>
<p style="margin-left:11%; margin-top: 1em">To transform
several 2-column, binary, double precision files with
(latitude,longitude) into (x,y) positions in inch on a
Transverse Mercator grid (central longitude 75W) for scale =
1:500000 and suppress those points that would fall outside
the map area, run</p>
<p style="margin-left:11%; margin-top: 1em"><b>mapproject</b>
tracks.* <b>−R</b>-80/-70/20/40
<b>−Jt</b>-75/1:500000 <b>−: −S −Di
−bo −bi</b> 2 > tmfile.b</p>
<p style="margin-left:11%; margin-top: 1em">To convert the
geodetic coordinates (lon, lat, height) in the file old.dat
from the NAD27 CONUS datum (Datum ID 131 which uses the
Clarke-1866 ellipsoid) to WGS 84, run</p>
<p style="margin-left:11%; margin-top: 1em"><b>mapproject</b>
old.dat <b>−Th</b> 131 > new.dat</p>
<p style="margin-left:11%; margin-top: 1em">To compute the
closest distance (in km) between each point in the input
file quakes.dat and the line segments given in the
multi-segment ASCII file coastline.xy, run</p>
<p style="margin-left:11%; margin-top: 1em"><b>mapproject</b>
quakes.dat <b>−L</b> coastline.xy/k >
quake_dist.dat</p>
<a name="RESTRICTIONS"></a>
<h2>RESTRICTIONS</h2>
<p style="margin-left:11%; margin-top: 1em">The rectangular
input region set with <b>−R</b> will in general be
mapped into a non-rectangular grid. Unless <b>−C</b>
is set, the leftmost point on this grid has xvalue = 0.0,
and the lowermost point will have yvalue = 0.0. Thus, before
you digitize a map, run the extreme map coordinates through
<b>mapproject</b> using the appropriate scale and see what
(x,y) values they are mapped onto. Use these values when
setting up for digitizing in order to have the inverse
transformation work correctly, or alternatively, use
<b>awk</b> to scale and shift the (x,y) values before
transforming. <br>
For some projections, a spherical solution may be used
despite the user having selected an ellipsoid. This occurs
when the users <b>−R</b> setting implies a region that
exceeds the domain in which the ellipsoidal series
expansions are valid. These are the conditions: (1) Lambert
Conformal Conic (<b>−JL</b>) and Albers Equal-Area
(<b>−JB</b>) will use the spherical solution when the
map scale exceeds 1.0E7. (2) Transverse Mercator
(<b>−JT</b>) and UTM (<b>−JU</b>) will will use
the spherical solution when either the west or east boundary
given in <b>−R</b> is more than 10 degrees from the
central meridian, and (3) same for Cassini
(<b>−JC</b>) but with a limit of only 4 degrees.</p>
<a name="ELLIPSOIDS AND SPHEROIDS"></a>
<h2>ELLIPSOIDS AND SPHEROIDS</h2>
<p style="margin-left:11%; margin-top: 1em"><b><A HREF="GMT.html">GMT</A></b> will
use ellipsoidal formulae if they are implemented and the
user have selected an ellipsoid as the reference shape (see
<b><A HREF="gmtdefaults.html#ELLIPSOID">ELLIPSOID</A></b> in <b><A HREF="gmtdefaults.html">gmtdefaults</A></b>). The user needs to
be aware of a few potential pitfalls: (1) For some
projections, such as Transverse Mercator, Albers, and
Lamberts conformal conic we use the ellipsoidal expressions
when the areas mapped are small, and switch to the spherical
expressions (and substituting the appropriate auxiliary
latitudes) for larger maps. The ellipsoidal formulae are
used as follows: (a) Transverse Mercator: When all points
are within 10 degrees of central meridian, (b) Conic
projections when longitudinal range is less than 90 degrees,
(c) Cassini projection when all points are within 4 degrees
of central meridian. (2) When you are trying to match some
historical data (e.g., coordinates obtained with a certain
projection and a certain reference ellipsoid) you may find
that <b><A HREF="GMT.html">GMT</A></b> gives results that are slightly different.
One likely source of this mismatch is that older
calculations often used less significant digits. For
instance, Snyder’s examples often use the Clarke 1866
ellipsoid (defined by him as having a flattening f =
1/294.98). From f we get the eccentricity squared to be
0.00676862818 (this is what <b><A HREF="GMT.html">GMT</A></b> uses), while Snyder
rounds off and uses 0.00676866. This difference can give
discrepancies of several tens of cm. If you need to
reproduce coordinates projected with this slightly different
eccentricity, you should specify your own ellipsoid with the
same parameters as Clarke 1866, but with f = 1/294.97861076.
Also, be aware that older data may be referenced to
different datums, and unless you know which datum was used
and convert all data to a common datum you may experience
mismatches of tens to hundreds of meters. (3) Finally, be
aware that <b><A HREF="gmtdefaults.html#MAP_SCALE_FACTOR">MAP_SCALE_FACTOR</A></b> have certain default
values for some projections so you may have to override the
setting in order to match results produced with other
settings.</p>
<a name="SEE ALSO"></a>
<h2>SEE ALSO</h2>
<p style="margin-left:11%; margin-top: 1em"><i><A HREF="gmtdefaults.html">gmtdefaults</A></i>(1),
<i><A HREF="GMT.html">GMT</A></i>(1), <i><A HREF="project.html">project</A></i>(1)</p>
<a name="REFERENCES"></a>
<h2>REFERENCES</h2>
<p style="margin-left:11%; margin-top: 1em">Bomford, G.,
1952, Geodesy, Oxford U. Press. <br>
Snyder, J. P., 1987, Map Projections − A Working
Manual, U.S. Geological Survey Prof. Paper 1395. <br>
Vanicek, P. and Krakiwsky, E, 1982, Geodesy − The
Concepts, North-Holland Publ., ISBN: 0 444 86149 1.</p>
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