1GRDROTATER(1) Generic Mapping Tools GRDROTATER(1)
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6 grdrotater - Rotate a grid using a finite rotation
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9 grdrotate ingrdfile -Goutgrdfile -Tplon/plat/omega [ -Fpolygonfile ] [
10 -H[i][nrec] ] [ -M[flag] ] [ -N ] [ -Q[b|c|l|n][[/]threshold] ] [
11 -Rwest/east/south/north[r] ] [ -S ] [ -V ] [ -:[i|o] ] [
12 -b[i|o][s|S|d|D[ncol]|c[var1/...]] ]
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15 grdrotater reads a geographical grid and reconstructs it given a total
16 reconstruction rotation. Optionally, the user may supply a clipping
17 polygon in multiple-segment format; then, only the part of the grid
18 inside the polygon is used to determine the return grid region. The
19 outline of the projected region is returned on stdout.
20 No space between the option flag and the associated arguments.
21 Use upper case for the option flags and lower case for modifiers.
22 ingrdfile
24 Name of a grid file in geographical (lon, lat) coordinates.
25 -G Name of output grid. This is the grid with the data recon‐
27 structed according to the specified rotation.
28 -T Finite rotation. Specify the longitude and latitude of the
30 rotation pole and the opening angle, all in degrees.
31
33 -F Specify a multi-segment closed polygon file that describes the
34 inside area of the grid that should be projected [Default
35 projects entire grid].
36 -H Input file(s) has Header record(s). Number of header records
38 can be changed by editing your .gmtdefaults4 file. If used, GMT
39 default is 1 header record. Use -Hi if only input data should
40 have header records [Default will write out header records if
41 the input data have them]. Blank lines and lines starting with #
42 are always skipped.
43 -M Multiple segment file. Segment separator is a record beginning
45 with flag. [Default is '>'].
46 -N Do Not output the rotated polygon outline [Default will write it
48 to stdout].
49 -Q Quick mode, use bilinear rather than bicubic interpolation
51 [Default]. Alternatively, select the interpolation mode by
52 adding b for B-spline smooting, c for bicubic interpolation, l
53 for bilinear interpolation or n for nearest-neighbor value.
54 Optionally, append threshold in the range [0,1]. This parameter
55 controls how close to nodes with NaN values the interpolation
56 will go. E.g., a threshold of 0.5 will interpolate about half
57 way from a non-NaN to a NaN node, whereas 0.1 will go about 90%
58 of the way, etc. [Default is 1, which means none of the (4 or
59 16) nearby nodes may be NaN]. -Q0 will just return the value of
60 the nearest node instead of interpolating. This is the same as
61 using -Qn.
62 -R west, east, south, and north specify the Region of interest, and
64 you may specify them in decimal degrees or in
65 [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left and
66 upper right map coordinates are given instead of w/e/s/n. The
67 two shorthands -Rg and -Rd stand for global domain (0/360 and
68 -180/+180 in longitude respectively, with -90/+90 in latitude).
69 -S Skip the rotation of the grid, just rotate the polygon outline
71 (requires -F).
72 -V Selects verbose mode, which will send progress reports to stderr
74 [Default runs "silently"].
75 -: Toggles between (longitude,latitude) and (latitude,longitude)
77 input/output. [Default is (longitude,latitude)].
78 -bi Selects binary input. Append s for single precision [Default is
80 d (double)]. Uppercase S or D will force byte-swapping.
81 Optionally, append ncol, the number of columns in your binary
82 input file if it exceeds the columns needed by the program. Or
83 append c if the input file is netCDF. Optionally, append
84 var1/var2/... to specify the variables to be read. [Default is
85 2 input columns].
86 -bo Selects binary output. Append s for single precision [Default
88 is d (double)]. Uppercase S or D will force byte-swapping.
89 Optionally, append ncol, the number of desired columns in your
90 binary output file. [Default is same as input].
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93 To rotate the data defined by grid topo.grd and the polygon outline
94 clip_path.d, using a finite rotation with pole at (135.5, -33.0) and a
95 rotation angle of 37.3 degrees and bicubic interpolation, try
96 grdrotater topo.grd -T135.5/-33/37.3 -V -Fclip_path.d -Grot_topo.grd >
98 rot_clip_path.d
99 To rotate the entire grid faa.grd using a finite rotation pole at
101 (67:45W, 22:35S) and a rotation angle of 19.6 degrees using a bilinear
102 interpolation, try
103 grdrotater faa.grd -T67:45W/22:35S/19.6 -V -Q -Grot_faa.grd >
105 rot_faa_path.d
106 To just see how the outline of the grid large.grd will plot after the
108 same rotation, try
109 grdrotater large.grd -T67:45W/22:35S/19.6 -V -S | psxy -Rg -JH180/6i
111 -B30 -M -W0.5p | gv -
112 Let say you have rotated gridA.grd and gridB.grd, restricting each
114 rotation to nodes inside polygons polyA.d and polyB.d, respectively,
115 using rotation A = (123W,22S,16,4) and rotation B = (108W, 16S, -14.5),
116 yielding rotated grids rot_gridA.grd and rot_gridB.grd. To determine
117 the region of overlap between the rotated grids, we use grdmath:
118 grdmath 1 rot_gridA.grd ISNAN SUB 1 rot_gridB.grd ISNAN SUB 2 EQ =
120 overlap.grd
121 The grid overlap.grd now has 1s in the regions of overlap and 0 else‐
123 where. You can use it as a mask or use grdcontour to extract a polygon
124 (contour).
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127 backtracker(1), hotspotter(1), originator(1) rotconverter(1)
128GMT 4.3.1 15 May 2008 GRDROTATER(1)