project(1) GMT project(1)
NAME
project - Project table data onto lines or great circles, generate
tracks, or translate coordinates
SYNOPSIS
project [ table ] -Ccx/cy [ -Aazimuth ] [ -Ebx/by ] [ -Fflags ] [
-Gdist[/colat][+h] ] [ -L[w][l_min/l_max] ] [ -N ] [ -Q ] [ -S ] [
-Tpx/py ] [ -V[level] ] [ -Ww_min/w_max ] [ -bbinary ] [ -dnodata ] [
-eregexp ] [ -fflags ] [ -ggaps ] [ -hheaders ] [ -iflags ] [ -sflags ]
[ -:[i|o] ]
Note: No space is allowed between the option flag and the associated
arguments.
DESCRIPTION
project reads arbitrary (x, y[,z]) data from standard input [or table ]
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 posi-
tion 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 coor-
dinate system is created which has its equator along that path, and the
zero meridian through the Center. Then the oblique longitude (p) corre-
sponds 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 pro-
jection 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.
Calculations of specific great-circle and geodesic distances or for
back-azimuths or azimuths are better done using mapproject.
project is CASE SENSITIVE. Use UPPER CASE for all one-letter designa-
tors which begin optional arguments. Use lower case for the xyzpqrs
letters in -flags.
REQUIRED ARGUMENTS
-Ccx/cy
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
pass. The cx/cy is not required to be 90 degrees from the pole.
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.
-Aazimuth
azimuth defines the azimuth of the projection (Definition 1).
-Ebx/by
bx/by defines the end point of the projection path (Definition
2).
-Fflags
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, see -bo) columns of values cor-
responding to xyzpqrs [Default]. 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.
-Gdist[/colat][+h]
Generate mode. No input is read. Create (r, s, p) output points
every dist units of p. See -Q option. Alternatively, append
/colat for a small circle instead [Default is a colatitude of
90, i.e., a great circle]. Use -C and -E to generate a circle
that goes through the center and end point. Note, in this case
the center and end point cannot be farther apart than 2*|colat|.
Finally, if you append +h the we will report the position of the
pole as part of the segment header [no header].
-L[w][l_min/l_max]
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.
-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 to be in the same units.
-S Sort the output into increasing p order. Useful when projecting
random data into a sequential profile.
-Tpx/py
px/py sets the position of the rotation pole of the projection.
(Definition 3).
-V[level] (more a|)
Select verbosity level [c].
-Ww_min/w_max
Width controls. Project only those points whose q coordinate is
within w_min < q < w_max.
-bi[ncols][t] (more a|)
Select native binary input. [Default is 2 input columns].
-bo[ncols][type] (more a|)
Select native binary output. [Default is given by -F or -G].
-d[i|o]nodata (more a|)
Replace input columns that equal nodata with NaN and do the
reverse on output.
-e[~]^<i>apattern^<i>a | -e[~]/regexp/[i] (more a|)
Only accept data records that match the given pattern.
-f[i|o]colinfo (more a|)
Specify data types of input and/or output columns.
-g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more a|)
Determine data gaps and line breaks.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more a|)
Skip or produce header record(s).
-icols[+l][+sscale][+ooffset][,^<i>a|] (more a|)
Select input columns and transformations (0 is first column).
-s[cols][a|r] (more a|)
Set handling of NaN records.
-:[i|o] (more a|)
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 just use -).
-+ or just +
Print an extensive usage (help) message, including the explana-
tion 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 all options, then exits.
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, absolute time is under the control of FOR-
MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point val-
ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for-
mat in effect can lead to loss of precision in ASCII 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 set-
ting.
EXAMPLES
To generate points every 10km along a great circle from 10N,50W to
30N,10W:
gmt 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 grd-
track, etc. ).
To generate points every 1 degree along a great circle from 30N,10W
with azimuth 30 and covering a full 360, try:
gmt project -C10W/30N -A30 -G1 -L-180/180 > great_circle.txt
To generate points every 10km along a small circle of colatitude 60
from 10N,50W to 30N,10W:
gmt project -C-50/10 -E-10/30 -G10/60 -Q > small_circle_points.xyp
To create a partial small circle of colatitude 80 about a pole at
40E,85N, with extent of 45 degrees to either side of the meridian
defined by the great circle from the pole to a point 15E,15N, try
gmt project -C15/15 -T40/85 -G1/80 -L-45/45 > some_circle.xyp
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, run:
gmt project c2610.xygmb -C-30/-30 -A-20 -W-10000/0 -L-500/500 -Fpz -Q > c2610_projected.pgmb
(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 this
example.)
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, use:
gmt 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, run:
gmt project pacific.lonlat -T-75/68 -C-149:26/-17:37 -Fpq > pacific.pq
Suppose that pacific_topo.nc is a grid file of bathymetry, and you want
to make a file of flowlines in the hotspot reference frame. If you run:
gmt grd2xyz pacific_topo.nc | project -T-75/68 -C0/-90 -Fxyq | xyz2grd -Retc -Ietc -Cflow.nc
then flow.nc is a file in the same area as pacific_topo.nc, but flow
contains the latitudes about the pole of the projection. You now can
use grdcontour on flow.nc 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 coordi-
nates 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.
SEE ALSO
fitcircle(1), gmt(1), gmtvector(1), grdtrack(1), mapproject(1),
grdproject(1), grdtrack(1)
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 project(1)
gmt5 5.4.2 - Generated Thu Jun 29 15:01:04 CDT 2017