NAME
project - project data along a line or great circle, generate a profile
track, or translate coordinates.
SYNOPSIS
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] ] [
-bo[s][n] ] [ -f[i|o]colinfo ]
DESCRIPTION
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. Projec-
tions 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 coordi-
nate 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 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.
-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
pass.
OPTIONS
infile 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, see -bo) columns of values cor-
responding 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 coordi-
nate). -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
2).
-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 .gmtdefaults4 file. If used, GMT
default is 1 header record. Use -Hi if only input data should
have header records [Default will write out header records if
the input data have them].
-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 and
-bo[s]n must set the number of output columns explicitly.
-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.
-T px/py sets the position of the roTation pole of the projection.
(Definition 3).
-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 and/or output. [Default is (longitude,latitude)]. Append
i to select input only or o to select output only. [Default
affects both].
-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
double]. Append n for the number of columns in the binary
file(s).
-f Special formatting of input and output columns (time or geo-
graphical data) Specify i(nput) or o(utput) [Default is both
input and output]. Give one or more columns (or column ranges)
separated by commas. Append T (Absolute calendar time), t (time
relative to chosen TIME_EPOCH), x (longitude), y (latitude), g
(geographic coordinate), or f (floating point) to each column or
column range item.
EXAMPLES
To generate points every 10km along a great circle from 10N,50W to
30N,10W:
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 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:
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:
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:
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 run:
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 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 coor-
dinates for an oblique small circle.
SEE ALSO
fitcircle(l), gmt(l), mapproject(l), grdproject(l)
GMT4.0 1 Oct 2004 PROJECT(l)
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