1PROJECT(1) Generic Mapping Tools PROJECT(1)
2
6 project - project data along a line or great circle, generate a profile
7 track, or translate coordinates.
8
10 project [ infile ] -Ccx/cy [ -Aazimuth ] [ -Dd|g ] [ -Ebx/by ] [
11 -Fflags ] [ -Gdist ] [ -H[i][nrec] ] [ -L[w][l_min/l_max] ] [
12 -M[i|o][flag] ] [ -N ] [ -Q ] [ -S ] [ -Tpx/py ] [ -V ] [ -Ww_min/w_max
13 ] [ -:[i|o] ] [ -b[i|o][s|S|d|D[ncol]|c[var1/...]] ] [ -f[i|o]colinfo ]
14
16 project reads arbitrary (x, y[, z]) data from standard input [or infile
17 ] and writes to standard output any combination of (x, y, z, p, q, r,
18 s), where (p, q) are the coordinates in the projection, (r, s) is the
19 position in the (x, y) coordinate system of the point on the profile (q
20 = 0 path) closest to (x, y), and z is all remaining columns in the
21 input (beyond the required x and y columns). Alternatively, project
22 may be used to generate (r, s, p) triples at equal increments dist
23 along a profile. In this case ( -G option), no input is read. Projec‐
24 tions are defined in any (but only) one of three ways: (Definition 1)
25 By a Center -C and an Azimuth -A in degrees clockwise from North.
26 (Definition 2) By a Center -C and end point E of the projection path
27 -E. (Definition 3) By a Center -C and a roTation pole position -T.
28 To spherically project data along a great circle path, an oblique coor‐
29 dinate system is created which has its equator along that path, and the
30 zero meridian through the Center. Then the oblique longitude (p) cor‐
31 responds to the distance from the Center along the great circle, and
32 the oblique latitude (q) corresponds to the distance perpendicular to
33 the great circle path. When moving in the increasing (p) direction,
34 (toward B or in the azimuth direction), the positive (q) direction is
35 to your left. If a Pole has been specified, then the positive (q)
36 direction is toward the pole.
37 To specify an oblique projection, use the -T option to set the Pole.
38 Then the equator of the projection is already determined and the -C
39 option is used to locate the p = 0 meridian. The Center cx/cy will be
40 taken as a point through which the p = 0 meridian passes. If you do
41 not care to choose a particular point, use the South pole (ox = 0, oy =
42 -90).
43 Data can be selectively windowed by using the -L and -W options. If -W
44 is used, the projection Width is set to use only points with w_min < q
45 < w_max. If -L is set, then the Length is set to use only those points
46 with l_min < p < l_max. If the -E option has been used to define the
47 projection, then -Lw may be selected to window the length of the pro‐
48 jection to exactly the span from O to B.
49 Flat Earth (Cartesian) coordinate transformations can also be made.
50 Set -N and remember that azimuth is clockwise from North (the y axis),
51 NOT the usual cartesian theta, which is counterclockwise from the x
52 axis. azimuth = 90 - theta.
53 No assumptions are made regarding the units for x, y, r, s, p, q, dist,
54 l_min, l_max, w_min, w_max. If -Q is selected, map units are assumed
55 and x, y, r, s must be in degrees and p, q, dist, l_min, l_max, w_min,
56 w_max will be in km.
57 Calculations of specific great-circle and geodesic distances or for
58 back-azimuths or azimuths are better done using mapproject.
59 project is CASE SENSITIVE. Use UPPER CASE for all one-letter designa‐
60 tors which begin optional arguments. Use lower case for the xyzpqrs
61 letters in -flags.
62 -C cx/cy sets the origin of the projection, in Definition 1 or 2.
65 If Definition 3 is used (-T), then cx/cy are the coordinates of
66 a point through which the oblique zero meridian (p = 0) should
67 pass.
68
70 infile name of ASCII (or binary, see -bi) file(s) with 2 or more col‐
71 umns holding (x,y,[z]) data values. If no filenames are given,
72 project will read from standard input. If the -G option is
73 selected, no input data are read.
74 -F Specify your desired output using any combination of xyzpqrs, in
76 any order. Do not space between the letters. Use lower case.
77 The output will be ASCII (or binary, see -bo) columns of values
78 corresponding to xyzpqrs [Default]. If both input and output
79 are using ASCII format then the z data are treated as
80 textstring(s). If the -G option is selected, the output will be
81 rsp.
82 -A azimuth defines the azimuth of the projection (Definition 1).
84 -D Set the location of the Discontinuity in longitude (r coordi‐
86 nate). -Dd will place the discontinuity at the Dateline, (-180
87 < r < 180); -Dg will place it at Greenwich, (0 < r < 360).
88 Default usually falls at dateline due to atan2 calls.
89 -E bx/by defines the end point of the projection path (Definition
91 2).
92 -G dist Generate mode. No input is read. Create (r, s, p) output
94 points every dist units of p. See -Q option.
95 -H Input file(s) has Header record(s). Number of header records
97 can be changed by editing your .gmtdefaults4 file. If used, GMT
98 default is 1 header record. Use -Hi if only input data should
99 have header records [Default will write out header records if
100 the input data have them]. Blank lines and lines starting with #
101 are always skipped.
102 -L Length controls. Project only those points whose p coordinate
104 is within l_min < p < l_max. If -E has been set, then you may
105 use -Lw to stay within the distance from C to E.
106 -M Multiple segment file(s). Segments are separated by a special
108 record. For ASCII files the first character must be flag
109 [Default is '>']. For binary files all fields must be NaN and
110 -b must set the number of output columns explicitly. By default
111 the -M setting applies to both input and output. Use -Mi and
112 -Mo to give separate settings.
113 -N Flat Earth. Make a Cartesian coordinate transformation in the
115 plane. [Default uses spherical trigonometry.]
116 -Q Map type units, i.e., project assumes x, y, r, s are in degrees
118 while p, q, dist, l_min, l_max, w_min, w_max are in km. If -Q
119 is not set, then all these are assumed to be in the same units.
120 -S Sort the output into increasing p order. Useful when projecting
122 random data into a sequential profile.
123 -T px/py sets the position of the roTation pole of the projection.
125 (Definition 3).
126 -V Selects verbose mode, which will send progress reports to stderr
128 [Default runs "silently"].
129 -W Width controls. Project only those points whose q coordinate is
131 within w_min < q < w_max.
132 -: Toggles between (longitude,latitude) and (latitude,longitude)
134 input and/or output. [Default is (longitude,latitude)]. Append
135 i to select input only or o to select output only. [Default
136 affects both].
137 -bi Selects binary input. Append s for single precision [Default is
139 d (double)]. Uppercase S or D will force byte-swapping.
140 Optionally, append ncol, the number of columns in your binary
141 input file if it exceeds the columns needed by the program. Or
142 append c if the input file is netCDF. Optionally, append
143 var1/var2/... to specify the variables to be read. [Default is
144 2 input columns].
145 -bo Selects binary output. Append s for single precision [Default
147 is d (double)]. Uppercase S or D will force byte-swapping.
148 Optionally, append ncol, the number of desired columns in your
149 binary output file. [Default is given by -F or -G].
150 -f Special formatting of input and/or output columns (time or geo‐
152 graphical data). Specify i or o to make this apply only to
153 input or output [Default applies to both]. Give one or more
154 columns (or column ranges) separated by commas. Append T (abso‐
155 lute calendar time), t (relative time in chosen TIME_UNIT since
156 TIME_EPOCH), x (longitude), y (latitude), or f (floating point)
157 to each column or column range item. Shorthand -f[i|o]g means
158 -f[i|o]0x,1y (geographic coordinates).
159
161 The ASCII output formats of numerical data are controlled by parameters
162 in your .gmtdefaults4 file. Longitude and latitude are formatted
163 according to OUTPUT_DEGREE_FORMAT, whereas other values are formatted
164 according to D_FORMAT. Be aware that the format in effect can lead to
165 loss of precision in the output, which can lead to various problems
166 downstream. If you find the output is not written with enough preci‐
167 sion, consider switching to binary output (-bo if available) or specify
168 more decimals using the D_FORMAT setting.
169
171 To generate points every 10km along a great circle from 10N,50W to
172 30N,10W:
173 project -C-50/10 -E-10/30 -G10 -Q > great_circle_points.xyp
175 (Note that great_circle_points.xyp could now be used as input for grd‐
177 track, etc. ).
178 To project the shiptrack gravity, magnetics, and bathymetry in
180 c2610.xygmb along a great circle through an origin at 30S, 30W, the
181 great circle having an azimuth of N20W at the origin, keeping only the
182 data from NE of the profile and within +/- 500 km of the origin, run:
183 project c2610.xygmb -C-30/-30 -A-20 -W-10000/0 -L-500/500 -Fpz -Q >
185 c2610_projected.pgmb
186 (Note in this example that -W-10000/0 is used to admit any value with a
188 large negative q coordinate. This will take those points which are on
189 our right as we walk along the great circle path, or to the NE in this
190 example.)
191 To make a Cartesian coordinate transformation of mydata.xy so that the
193 new origin is at 5,3 and the new x axis (p) makes an angle of 20
194 degrees with the old x axis, use:
195 project mydata.xy -C5/3 -A70 -Fpq > mydata.pq
197 To take data in the file pacific.lonlat and transform it into oblique
199 coordinates using a pole from the hotspot reference frame and placing
200 the oblique zero meridian (p = 0 line) through Tahiti, run:
201 project pacific.lonlat -T-75/68 -C-149:26/-17:37 -Fpq > pacific.pq
203 Suppose that pacific_topo.grd is a grid file of bathymetry, and you
205 want to make a file of flowlines in the hotspot reference frame. If
206 you run:
207 grd2xyz pacific_topo.grd | project -T-75/68 -C0/-90 -Fxyq | xyz2grd
209 -Retc -Ietc -Cflow.grd
210 then flow.grd is a file in the same area as pacific_topo.grd, but flow
212 contains the latitudes about the pole of the projection. You now can
213 use grdcontour on flow.grd to draw lines of constant oblique latitude,
214 which are flow lines in the hotspot frame.
215 If you have an arbitrarily rotation pole px/py and you would like to
217 draw an oblique small circle on a map, you will first need to make a
218 file with the oblique coordinates for the small circle (i.e., lon =
219 0-360, lat is constant), then create a file with two records: the north
220 pole (0/90) and the origin (0/0), and find what their oblique coordi‐
221 nates are using your rotation pole. Now, use the projected North pole
222 and origin coordinates as the rotation pole and center, respectively,
223 and project your file as in the pacific example above. This gives
224 coordinates for an oblique small circle.
225
227 fitcircle(1), GMT(1), mapproject(1), grdproject(1)
228GMT 4.3.1 15 May 2008 PROJECT(1)