1PROJECT(1) GMT PROJECT(1)
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6 project - Project table data onto lines or great circles, generate
7 tracks, or translate coordinates
8
10 project [ table ] -Ccx/cy [ -Aazimuth ] [ -Ebx/by ] [ -Fflags ] [
11 -Gdist[/colat][+h] ] [ -L[w][l_min/l_max] ] [ -N ] [ -Q ] [ -S ] [
12 -Tpx/py ] [ -V[level] ] [ -Ww_min/w_max ] [ -bbinary ] [ -dnodata ] [
13 -eregexp ] [ -fflags ] [ -ggaps ] [ -hheaders ] [ -iflags ] [ -sflags ]
14 [ -:[i|o] ]
15 Note: No space is allowed between the option flag and the associated
17 arguments.
18
20 project reads arbitrary (x, y[,z]) data from standard input [or table ]
21 and writes to standard output any combination of (x, y, z, p, q, r, s),
22 where (p, q) are the coordinates in the projection, (r, s) is the posi‐
23 tion in the (x, y) coordinate system of the point on the profile (q = 0
24 path) closest to (x, y), and z is all remaining columns in the input
25 (beyond the required x and y columns).
26 Alternatively, project may be used to generate (r, s, p) triples at
28 equal increments dist along a profile. In this case ( -G option), no
29 input is read.
30 Projections are defined in any (but only) one of three ways:
32 (Definition 1) By a Center -C and an Azimuth -A in degrees clockwise
34 from North.
35 (Definition 2) By a Center -C and end point E of the projection path
37 -E.
38 (Definition 3) By a Center -C and a roTation pole position -T.
40 To spherically project data along a great circle path, an oblique coor‐
42 dinate system is created which has its equator along that path, and the
43 zero meridian through the Center. Then the oblique longitude (p) corre‐
44 sponds to the distance from the Center along the great circle, and the
45 oblique latitude (q) corresponds to the distance perpendicular to the
46 great circle path. When moving in the increasing (p) direction, (toward
47 B or in the azimuth direction), the positive (q) direction is to your
48 left. If a Pole has been specified, then the positive (q) direction is
49 toward the pole.
50 To specify an oblique projection, use the -T option to set the Pole.
52 Then the equator of the projection is already determined and the -C
53 option is used to locate the p = 0 meridian. The Center cx/cy will be
54 taken as a point through which the p = 0 meridian passes. If you do not
55 care to choose a particular point, use the South pole (ox = 0, oy =
56 -90).
57 Data can be selectively windowed by using the -L and -W options. If -W
59 is used, the projection Width is set to use only points with w_min < q
60 < w_max. If -L is set, then the Length is set to use only those points
61 with l_min < p < l_max. If the -E option has been used to define the
62 projection, then -Lw may be selected to window the length of the pro‐
63 jection to exactly the span from O to B.
64 Flat Earth (Cartesian) coordinate transformations can also be made. Set
66 -N and remember that azimuth is clockwise from North (the y axis), NOT
67 the usual cartesian theta, which is counterclockwise from the x axis.
68 azimuth = 90 - theta.
69 No assumptions are made regarding the units for x, y, r, s, p, q, dist,
71 l_min, l_max, w_min, w_max. If -Q is selected, map units are assumed
72 and x, y, r, s must be in degrees and p, q, dist, l_min, l_max, w_min,
73 w_max will be in km.
74 Calculations of specific great-circle and geodesic distances or for
76 back-azimuths or azimuths are better done using mapproject.
77 project is CASE SENSITIVE. Use UPPER CASE for all one-letter designa‐
79 tors which begin optional arguments. Use lower case for the xyzpqrs
80 letters in -flags.
81
83 -Ccx/cy
84 cx/cy sets the origin of the projection, in Definition 1 or 2.
85 If Definition 3 is used (-T), then cx/cy are the coordinates of
86 a point through which the oblique zero meridian (p = 0) should
87 pass. The cx/cy is not required to be 90 degrees from the pole.
88
90 table One or more ASCII (or binary, see -bi[ncols][type]) data table
91 file(s) holding a number of data columns. If no tables are given
92 then we read from standard input.
93 -Aazimuth
95 azimuth defines the azimuth of the projection (Definition 1).
96 -Ebx/by
98 bx/by defines the end point of the projection path (Definition
99 2).
100 -Fflags
102 Specify your desired output using any combination of xyzpqrs, in
103 any order. Do not space between the letters. Use lower case. The
104 output will be ASCII (or binary, see -bo) columns of values cor‐
105 responding to xyzpqrs [Default]. If both input and output are
106 using ASCII format then the z data are treated as textstring(s).
107 If the -G option is selected, the output will be rsp.
108 -Gdist[/colat][+h]
110 Generate mode. No input is read. Create (r, s, p) output points
111 every dist units of p. See -Q option. Alternatively, append
112 /colat for a small circle instead [Default is a colatitude of
113 90, i.e., a great circle]. Use -C and -E to generate a circle
114 that goes through the center and end point. Note, in this case
115 the center and end point cannot be farther apart than 2*|colat|.
116 Finally, if you append +h the we will report the position of the
117 pole as part of the segment header [no header].
118 -L[w][l_min/l_max]
120 Length controls. Project only those points whose p coordinate is
121 within l_min < p < l_max. If -E has been set, then you may use
122 -Lw to stay within the distance from C to E.
123 -N Flat Earth. Make a Cartesian coordinate transformation in the
125 plane. [Default uses spherical trigonometry.]
126 -Q Map type units, i.e., project assumes x, y, r, s are in degrees
128 while p, q, dist, l_min, l_max, w_min, w_max are in km. If -Q is
129 not set, then all these are assumed to be in the same units.
130 -S Sort the output into increasing p order. Useful when projecting
132 random data into a sequential profile.
133 -Tpx/py
135 px/py sets the position of the rotation pole of the projection.
136 (Definition 3).
137 -V[level] (more ...)
139 Select verbosity level [c].
140 -Ww_min/w_max
142 Width controls. Project only those points whose q coordinate is
143 within w_min < q < w_max.
144 -bi[ncols][t] (more ...)
146 Select native binary input. [Default is 2 input columns].
147 -bo[ncols][type] (more ...)
149 Select native binary output. [Default is given by -F or -G].
150 -d[i|o]nodata (more ...)
152 Replace input columns that equal nodata with NaN and do the
153 reverse on output.
154 -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
156 Only accept data records that match the given pattern.
157 -f[i|o]colinfo (more ...)
159 Specify data types of input and/or output columns.
160 -g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more ...)
162 Determine data gaps and line breaks.
163 -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
165 Skip or produce header record(s).
166 -icols[+l][+sscale][+ooffset][,...] (more ...)
168 Select input columns and transformations (0 is first column).
169 -s[cols][a|r] (more ...)
171 Set handling of NaN records.
172 -:[i|o] (more ...)
174 Swap 1st and 2nd column on input and/or output.
175 -^ or just -
177 Print a short message about the syntax of the command, then
178 exits (NOTE: on Windows just use -).
179 -+ or just +
181 Print an extensive usage (help) message, including the explana‐
182 tion of any module-specific option (but not the GMT common
183 options), then exits.
184 -? or no arguments
186 Print a complete usage (help) message, including the explanation
187 of all options, then exits.
188
190 The ASCII output formats of numerical data are controlled by parameters
191 in your gmt.conf file. Longitude and latitude are formatted according
192 to FORMAT_GEO_OUT, absolute time is under the control of FOR‐
193 MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point val‐
194 ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for‐
195 mat in effect can lead to loss of precision in ASCII output, which can
196 lead to various problems downstream. If you find the output is not
197 written with enough precision, consider switching to binary output (-bo
198 if available) or specify more decimals using the FORMAT_FLOAT_OUT set‐
199 ting.
200
202 To generate points every 10km along a great circle from 10N,50W to
203 30N,10W:
204 gmt project -C-50/10 -E-10/30 -G10 -Q > great_circle_points.xyp
206 (Note that great_circle_points.xyp could now be used as input for grd‐
208 track, etc. ).
209 To generate points every 1 degree along a great circle from 30N,10W
211 with azimuth 30 and covering a full 360, try:
212 gmt project -C10W/30N -A30 -G1 -L-180/180 > great_circle.txt
214 To generate points every 10km along a small circle of colatitude 60
216 from 10N,50W to 30N,10W:
217 gmt project -C-50/10 -E-10/30 -G10/60 -Q > small_circle_points.xyp
219 To create a partial small circle of colatitude 80 about a pole at
221 40E,85N, with extent of 45 degrees to either side of the meridian
222 defined by the great circle from the pole to a point 15E,15N, try
223 gmt project -C15/15 -T40/85 -G1/80 -L-45/45 > some_circle.xyp
225 To project the shiptrack gravity, magnetics, and bathymetry in
227 c2610.xygmb along a great circle through an origin at 30S, 30W, the
228 great circle having an azimuth of N20W at the origin, keeping only the
229 data from NE of the profile and within +/- 500 km of the origin, run:
230 gmt project c2610.xygmb -C-30/-30 -A-20 -W-10000/0 -L-500/500 -Fpz -Q > c2610_projected.pgmb
232 (Note in this example that -W-10000/0 is used to admit any value with a
234 large negative q coordinate. This will take those points which are on
235 our right as we walk along the great circle path, or to the NE in this
236 example.)
237 To make a Cartesian coordinate transformation of mydata.xy so that the
239 new origin is at 5,3 and the new x axis (p) makes an angle of 20
240 degrees with the old x axis, use:
241 gmt project mydata.xy -C5/3 -A70 -Fpq > mydata.pq
243 To take data in the file pacific.lonlat and transform it into oblique
245 coordinates using a pole from the hotspot reference frame and placing
246 the oblique zero meridian (p = 0 line) through Tahiti, run:
247 gmt project pacific.lonlat -T-75/68 -C-149:26/-17:37 -Fpq > pacific.pq
249 Suppose that pacific_topo.nc is a grid file of bathymetry, and you want
251 to make a file of flowlines in the hotspot reference frame. If you run:
252 gmt grd2xyz pacific_topo.nc | project -T-75/68 -C0/-90 -Fxyq | xyz2grd -Retc -Ietc -Cflow.nc
254 then flow.nc is a file in the same area as pacific_topo.nc, but flow
256 contains the latitudes about the pole of the projection. You now can
257 use grdcontour on flow.nc to draw lines of constant oblique latitude,
258 which are flow lines in the hotspot frame.
259 If you have an arbitrarily rotation pole px/py and you would like to
261 draw an oblique small circle on a map, you will first need to make a
262 file with the oblique coordinates for the small circle (i.e., lon =
263 0-360, lat is constant), then create a file with two records: the north
264 pole (0/90) and the origin (0/0), and find what their oblique coordi‐
265 nates are using your rotation pole. Now, use the projected North pole
266 and origin coordinates as the rotation pole and center, respectively,
267 and project your file as in the pacific example above. This gives
268 coordinates for an oblique small circle.
269
271 fitcircle, gmt, gmtvector, grdtrack, mapproject, grdproject, grdtrack
272
274 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
2755.4.5 Feb 24, 2019 PROJECT(1)