Provided by: gmt-common_5.2.1+dfsg-3build1_all 
NAME
mapproject - Do forward and inverse map transformations, datum conversions and geodesy
SYNOPSIS
mapproject [ tables ] parameters region [ b|B|f|F|o|O[lon0/lat0] ] [ [dx/dy] ] [ c|i|p ] [ [datum] ] [
[unit] ] [ [x0/y0/][[+|-]unit][+|-] ] [ ] [ line.xy[/[+|-]unit][+] ] [ [a|c|g|m] ] [ [d|e ] [ ] [
[h]from[/to] ] [ [level] ] [ [w|h] ] [ -b<binary> ] [ -d<nodata> ] [ -f<flags> ] [ -g<gaps> ] [
-h<headers> ] [ -i<flags> ] [ -o<flags> ] [ -p<flags> ] [ -s<flags> ] [ -:[i|o] ]
Note: No space is allowed between the option flag and the associated arguments.
DESCRIPTION
mapproject reads (longitude, latitude) positions from tables [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 -: on how to read (latitude,longitude)
files.
REQUIRED ARGUMENTS
-Jparameters (more ...)
Select map projection.
-R[unit]xmin/xmax/ymin/ymax[r] (more ...)
Specify the region of interest. Special case for the UTM projection: If -C is used and -R 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).
OPTIONAL ARGUMENTS
table One or more ASCII (or binary, see -bi[ncols][type]) data table file(s) holding a number of data
columns. If no tables are given then we read from standard input.
-Ab|B|f|F|o|O[lon0/lat0]
-Af calculates the (forward) azimuth from fixed point lon/lat to each data point. Use -Ab to get
back-azimuth from data points to fixed point. Use -Ao to get orientations (-90/90) rather than
azimuths (0/360). Upper case F, B or O 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.
-C[dx/dy]
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 -I 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
PROJ_LENGTH_UNIT) unless -F is used, in which case the offsets are in meters.
-Dc|i|p
Temporarily override PROJ_LENGTH_UNIT and use c (cm), i (inch), or p (points) instead. Cannot be
used with -F.
-E[datum]
Convert from geodetic (lon, lat, height) to Earth Centered Earth Fixed (ECEF) (x,y,z) coordinates
(add -I for the inverse conversion). Append datum ID (see -Qd) or give ellipsoid:dx,dy,dz where
ellipsoid may be an ellipsoid ID (see -Qe) or given as a[,*inv_f*], where a is the semi-major axis
and inv_f is the inverse flattening (0 if omitted). If datum is - or not given we assume WGS-84.
-F[unit]
Force 1:1 scaling, i.e., output (or input, see -I) data are in actual projected meters. To specify
other units, append the desired unit (see UNITS). Without -F, the output (or input, see -I) are in
the units specified by PROJ_LENGTH_UNIT (but see -D).
-G[x0/y0/][[+|-]unit][+|-]
Calculate distances along track or to the optional point set with -Gx0/y0. Append the distance
unit (see UNITS), including c (Cartesian distance using input coordinates) or C (Cartesian
distance using projected coordinates). The C unit requires -R and -J to be set. With no fixed
point is given we calculate cumulate distances along track. Append - to obtain incremental
distance between successive points. Append + to specify the 2nd point via two extra columns in the
input file.
-I Do the Inverse transformation, i.e., get (longitude,latitude) from (x,y) data.
-Lline.xy[/[+|-]unit][+]
Determine the shortest distance from the input data points to the line(s) given in the ASCII
multisegment file line.xy. The distance and the coordinates of the nearest point will be appended
to the output as three new columns. Append the distance unit (see UNITS), including c (Cartesian
distance using input coordinates) or C (Cartesian distance using projected coordinates). The C
unit requires -R and -J to be set. Finally, append + to report the line segment id and the
fractional point number instead of lon/lat of the nearest point.
-N[a|c|g|m]
Convert from geodetic latitudes (using the current ellipsoid; see PROJ_ELLIPSOID) to one of four
different auxiliary latitudes (longitudes are unaffected). Choose from authalic, conformal,
geocentric, and meridional latitudes [geocentric]. Use -I to convert from auxiliary latitudes to
geodetic latitudes.
-Q[d|e List all projection parameters. To only list datums, use -Qd. To only list ellipsoids, use -Qe.
-S Suppress points that fall outside the region.
-T[h]from[/to]
Coordinate conversions between datums from and to using the standard Molodensky transformation.
Use -Th if 3rd input column has height above ellipsoid [Default assumes height = 0, i.e., on the
ellipsoid]. Specify datums using the datum ID (see -Qd) or give ellipsoid:dx,dy,dz where ellipsoid
may be an ellipsoid ID (see -Qe) or given as a[,*inv_f*], where a is the semi-major axis and inv_f
is the inverse flattening (0 if omitted). If datum is - or not given we assume WGS-84. -T may be
used in conjunction with -R -J to change the datum before coordinate projection (add -I to apply
the datum conversion after the inverse projection). Make sure that the PROJ_ELLIPSOID setting is
correct for your case.
-V[level] (more ...)
Select verbosity level [c].
-W[w|h]
Prints map width and height on standard output. No input files are read. To only output the
width or the height, append w or h, respectively. The units of the dimensions may be changed via
-D.
-bi[ncols][t] (more ...)
Select native binary input. [Default is 2 input columns].
-bo[ncols][type] (more ...)
Select native binary output. [Default is same as input].
-d[i|o]nodata (more ...)
Replace input columns that equal nodata with NaN and do the reverse on output.
-f[i|o]colinfo (more ...)
Specify data types of input and/or output columns.
-g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more ...)
Determine data gaps and line breaks.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
Skip or produce header record(s).
-icols[l][sscale][ooffset][,...] (more ...)
Select input columns (0 is first column).
-ocols[,...] (more ...)
Select output columns (0 is first column).
-p[x|y|z]azim/elev[/zlevel][+wlon0/lat0[/z0]][+vx0/y0] (more ...)
Select perspective view.
-s[cols][a|r] (more ...)
Set handling of NaN records.
-:[i|o] (more ...)
Swap 1st and 2nd column on input and/or output.
-^ or just -
Print a short message about the syntax of the command, then exits (NOTE: on Windows use just -).
-+ or just +
Print an extensive usage (help) message, including the explanation of any module-specific option
(but not the GMT common options), then exits.
-? or no arguments
Print a complete usage (help) message, including the explanation of options, then exits.
--version
Print GMT version and exit.
--show-datadir
Print full path to GMT share directory and exit.
UNITS
For map distance unit, append unit d for arc degree, m for arc minute, and s for arc second, or e for
meter [Default], f for foot, k for km, M for statute mile, n for nautical mile, and u for US survey foot.
By default we compute such distances using a spherical approximation with great circles. Prepend - to a
distance (or the unit is no distance is given) to perform "Flat Earth" calculations (quicker but less
accurate) or prepend + to perform exact geodesic calculations (slower but more accurate).
ASCII FORMAT PRECISION
The ASCII output formats of numerical data are controlled by parameters in your gmt.conf file. Longitude
and latitude are formatted according to FORMAT_GEO_OUT, whereas other values are formatted according to
FORMAT_FLOAT_OUT. 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 (-bo if available) or specify more decimals using the
FORMAT_FLOAT_OUT setting.
EXAMPLES
To convert UTM coordinates in meters to geographic locations, given a file utm.txt and knowing the UTM
zone (and zone or hemisphere), try
gmt mapproject utm.txt -Ju+11/1:1 -C -I -F
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
gmt mapproject lonlatfile -R20/50/12/25 -Jm0.5c > xyfile
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
gmt mapproject tracks.* -R-80/-70/20/40 -Jt-75/1:500000 -: -S -Di -bo -bi2 > tmfile.b
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
gmt mapproject old.dat -Th131 > new.dat
To compute the closest distance (in km) between each point in the input file quakes.dat and the line
segments given in the multisegment ASCII file coastline.xy, run
gmt mapproject quakes.dat -Lcoastline.xy/k > quake_dist.dat
RESTRICTIONS
The rectangular input region set with -R will in general be mapped into a non-rectangular grid. Unless -C
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 mapproject 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 awk to scale and shift the
(x,y) values before transforming.
For some projection, a spherical solution may be used despite the user having selected an ellipsoid. This
occurs when the users -R setting implies a region that exceeds the domain in which the ellipsoidal series
expansions are valid. These are the conditions: (1) Lambert Conformal Conic (-JL)and Albers Equal-Area
(-JB) will use the spherical solution when the map scale exceeds 1.0E7. (2) Transverse Mercator (-JT) and
UTM (-JU) will will use the spherical solution when either the west or east boundary given in -R is more
than 10 degrees from the central meridian, and (3) same for Cassini (-JC) but with a limit of only 4
degrees.
ELLIPSOIDS AND SPHEROIDS
GMT will use ellipsoidal formulae if they are implemented and the user have selected an ellipsoid as the
reference shape (see PROJ_ELLIPSOID). The user needs to be aware of a few potential pitfalls: (1) For
some projections, such as Transverse Mercator, Albers, and Lambert's 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 GMT
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 GMT 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 PROJ_SCALE_FACTOR have certain
default values for some projections so you may have to override the setting in order to match results
produced with other settings.
SEE ALSO
gmt, gmt.conf, gmtvector, project
REFERENCES
Bomford, G., 1952, Geodesy, Oxford U. Press.
Snyder, J. P., 1987, Map Projections - A Working Manual, U.S. Geological Survey Prof. Paper 1395.
Vanicek, P. and Krakiwsky, E, 1982, Geodesy - The Concepts, North-Holland Publ., ISBN: 0 444 86149 1.
COPYRIGHT
2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.2.1 January 28, 2016 MAPPROJECT(1gmt)