project - project data along a line or great circle, generate a
profile track, or translate coordinates.
project [ infile ] -Fflags -Ccx/cy [ -Aazimuth ] [ -Dd|g ] [ -Ebx/by ]
[ -Gdist ] [ -H[nrec] ] [ -L[w][l_min/l_max] ] [ -M[flag] ] [ -N ] [ -Q
] [ -S ] [ -Tpx/py ] [ -V ] [ -Ww_min/w_max ] [ -: ] [ -bi[s][n] ] [
project reads arbitrary (x, y[, z]) data from standard input [or
infile ] and writes to standard output any combination of (x, y, z, p,
q, r, s), where (p, q) are the coordinates in the projection, (r, s)
is the position in the (x, y) coordinate system of the point on the
profile (q = 0 path) closest to (x, y), and z is all remaining columns
in the input (beyond the required x and y columns). Alternatively,
project may be used to generate (r, s, p) triples at equal increments
dist along a profile. In this case ( -G option), no input is read.
Projections are defined in any (but only) one of three ways:
(Definition 1) By a Center -C and an Azimuth -A in degrees clockwise
from North. (Definition 2) By a Center -C and end point E of the
projection path -E. (Definition 3) By a Center -C and a roTation
pole position -T. To spherically project data along a great circle
path, an oblique coordinate system is created which has its equator
along that path, and the zero meridian through the Center. Then the
oblique longitude (p) corresponds to the distance from the Center
along the great circle, and the oblique latitude (q) corresponds to
the distance perpendicular to the great circle path. When moving in
the increasing (p) direction, (toward B or in the azimuth direction),
the positive (q) direction is to your left. If a Pole has been
specified, then the positive (q) direction is toward the pole. To
specify an oblique projection, use the -T option to set the Pole.
Then the equator of the projection is already determined and the -C
option is used to locate the p = 0 meridian. The Center cx/cy will be
taken as a point through which the p = 0 meridian passes. If you do
not care to choose a particular point, use the South pole (ox = 0, oy
= -90). Data can be selectively windowed by using the -L and -W
options. If -W is used, the projection Width is set to use only
points with w_min < q < w_max. If -L is set, then the Length is set
to use only those points with l_min < p < l_max. If the -E option has
been used to define the projection, then -Lw may be selected to window
the length of the projection to exactly the span from O to B. Flat
earth (cartesian) coordinate transformations can also be made. Set -N
and remember that azimuth is clockwise from North (the y axis), NOT
the usual cartesian theta, which is counterclockwise from the x axis.
azimuth = 90 - theta. No assumptions are made regarding the units for
x, y, r, s, p, q, dist, l_min,l _max, w_min, w_max. If -Q is
selected, map units are assumed and x, y, r, s must be in degrees and
p, q, dist, l_min, l_max, w_min, w_max will be in km. project is CASE
SENSITIVE. Use UPPER CASE for all one-letter designators which begin
optional arguments. Use lower case for the xyzpqrs letters in -flags.
-C cx/cy sets the origin of the projection, in Definition 1 or 2.
If Definition 3 is used (-T), then cx/cy are the coordinates of a
point through which the oblique zero meridian (p = 0) should
name of ASCII (or binary, see -bi) file(s) with 2 or more columns
holding (x,y,[z]) data values. If no filenames are given,
project will read from standard input. If the -G option is
selected, no input data are read.
-F Specify your desired output using any combination of xyzpqrs, in
any order. Do not space between the letters. Use lower case.
The output will be ASCII (or binary) columns of values
corresponding to xyzpqrs. If both input and output are using
ASCII format then the z data are treated as textstring(s). If
the -G option is selected, the output will be rsp.
-A azimuth defines the azimuth of the projection (Definition 1).
-D Set the location of the Discontinuity in longitude (r
coordinate). -Dd will place the discontinuity at the Dateline,
(-180 < r < 180); -Dg will place it at Greenwich, (0 < r < 360).
Default usually falls at dateline due to atan2 calls.
-E bx/by defines the end point of the projection path (Definition
-G dist Generate mode. No input is read. Create (r, s, p) output
points every dist units of p. See -Q option.
-H Input file(s) has Header record(s). Number of header records can
be changed by editing your .gmtdefaults file. If used, GMT
default is 1 header record.
-L Length controls. Project only those points whose p coordinate is
within l_min < p < l_max. If -E has been set, then you may use
-Lw to stay within the distance from C to E.
-M Multiple segment file(s). Segments are separated by a special
record. For ASCII files the first character must be flag
[Default is '>']. For binary files all fields must be NaN.
-N Flat earth. Make a cartesian coordinate transformation in the
plane. [Default uses spherical trigonometry.]
-Q Map type units, i.e., project assumes x, y, r, s are in degrees
while p, q, dist, l_min,l _max, w_min, w_max are in km. If -Q is
not set, then all these are assumed in same units.
-S Sort the output into increasing p order. Useful when projecting
random data into a sequential profile.
-T px/py sets the position of the roTation pole of the projection.
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
-W Width controls. Project only those points whose q coordinate is
within w_min < q < w_max.
-: Toggles between (longitude,latitude) and (latitude,longitude)
input/output. [Default is (longitude,latitude)].
-bi Selects binary input. Append s for single precision [Default is
double]. Append n for the number of columns in the binary
file(s). [Default is 2 input columns].
-bo Selects binary output. Append s for single precision [Default is
To generate points every 10km along a great circle from 10N,50W to
project -C-50/10 -E-10/30 -G10 -Q > great_circle_points.xyp
(Note that great_circle_points.xyp could now be used as input for
grdtrack, etc. ).
To project the shiptrack gravity, magnetics, and bathymetry in
c2610.xygmb along a great circle through an origin at 30S, 30W, the
great circle having an azimuth of N20W at the origin, keeping only the
data from NE of the profile and within +/- 500 km of the origin, try:
project c2610.xygmb -C-30/-30 -A-20 -W-10000/0 -L-500/500 -Fpz -Q >
(Note in this example that -W-10000/0 is used to admit any value with
a large negative q coordinate. This will take those points which are
on our right as we walk along the great circle path, or to the NE in
To make a cartesian coordinate transformation of mydata.xy so that the
new origin is at 5,3 and the new x axis (p) makes an angle of 20
degrees with the old x axis, try:
project mydata.xy -C5/3 -A70 -Fpq > mydata.pq
To take data in the file pacific.lonlat and transform it into oblique
coordinates using a pole from the hotspot reference frame and placing
the oblique zero meridian (p = 0 line) through Tahiti, try:
project pacific.lonlat -T-75/68 -C-149:26/-17:37 -Fpq > pacific.pq
Suppose that pacific_topo.grd is a grdfile of bathymetry, and you want
to make a file of flowlines in the hotspot reference frame. If you
grd2xyz pacific_topo.grd | project -T-75/68 -C0/-90 -Fxyq | xyz2grd
-Retc -Ietc -Cflow.grd
then flow.grd is a file in the same area as pacific_topo.grd, but flow
contains the latitudes about the pole of the projection. You now can
use grdcontour on flow.grd to draw lines of constant oblique latitude,
which are flow lines in the hotspot frame.
If you have an arbitrarily rotation pole px/py and you would like to
draw an oblique small circle on a map, you will first need to make a
file with the oblique coordinates for the small circle (i.e., lon =
0-360, lat is constant), then create a file with two records: the
north pole (0/90) and the origin (0/0), and find what their oblique
coordinates are using your rotation pole. Now, use the projected
North pole and origin coordinates as the rotation pole and center,
respectively, and project your file as in the pacific example above.
This gives coordinates for an oblique small circle.
fitcircle, gmt, mapproject, grdproject
Man(1) output converted with