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] ] [ -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/...]] ] [ -m[flag] ]
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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 provided the
20 rotated region is not the entire globe.
21 No space between the option flag and the associated arguments.
22 Use upper case for the option flags and lower case for modifiers.
23 ingrdfile
25 Name of a grid file in geographical (lon, lat) coordinates.
26 -G Name of output grid. This is the grid with the data recon‐
28 structed according to the specified rotation.
29 -T Finite rotation. Specify the longitude and latitude of the
31 rotation pole and the opening angle, all in degrees.
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34 -F Specify a multi-segment closed polygon file that describes the
35 inside area of the grid that should be projected [Default
36 projects entire grid].
37 -H Input file(s) has header record(s). If used, the default number
39 of header records is N_HEADER_RECS. Use -Hi if only input data
40 should have header records [Default will write out header
41 records if the input data have them]. Blank lines and lines
42 starting with # are always skipped.
43 -N Do Not output the rotated polygon outline [Default will write it
45 to stdout].
46 -Q Quick mode, use bilinear rather than bicubic interpolation
48 [Default]. Alternatively, select the interpolation mode by
49 adding b for B-spline smoothing, c for bicubic interpolation, l
50 for bilinear interpolation or n for nearest-neighbor value.
51 Optionally, append threshold in the range [0,1]. This parameter
52 controls how close to nodes with NaN values the interpolation
53 will go. E.g., a threshold of 0.5 will interpolate about half
54 way from a non-NaN to a NaN node, whereas 0.1 will go about 90%
55 of the way, etc. [Default is 1, which means none of the (4 or
56 16) nearby nodes may be NaN]. -Q0 will just return the value of
57 the nearest node instead of interpolating. This is the same as
58 using -Qn.
59 -R west, east, south, and north specify the Region of interest, and
61 you may specify them in decimal degrees or in
62 [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left and
63 upper right map coordinates are given instead of w/e/s/n. The
64 two shorthands -Rg and -Rd stand for global domain (0/360 and
65 -180/+180 in longitude respectively, with -90/+90 in latitude).
66 Alternatively, specify the name of an existing grid file and the
67 -R settings (and grid spacing, if applicable) are copied from
68 the grid.
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].
91 -m Multiple segment file(s). Segments are separated by a special
93 record. For ASCII files the first character must be flag
94 [Default is '>']. For binary files all fields must be NaN and
95 -b must set the number of output columns explicitly. By default
96 the -m setting applies to both input and output. Use -mi and
97 -mo to give separate settings to input and output.
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100 To rotate the data defined by grid topo.grd and the polygon outline
101 clip_path.d, using a finite rotation with pole at (135.5, -33.0) and a
102 rotation angle of 37.3 degrees and bicubic interpolation, try
103 grdrotater topo.grd -T135.5/-33/37.3 -V -Fclip_path.d -Grot_topo.grd >
105 rot_clip_path.d
106 To rotate the entire grid faa.grd using a finite rotation pole at
108 (67:45W, 22:35S) and a rotation angle of 19.6 degrees using a bilinear
109 interpolation, try
110 grdrotater faa.grd -T67:45W/22:35S/19.6 -V -Q -Grot_faa.grd >
112 rot_faa_path.d
113 To just see how the outline of the grid large.grd will plot after the
115 same rotation, try
116 grdrotater large.grd -T67:45W/22:35S/19.6 -V -S | psxy -Rg -JH180/6i
118 -B30 -m -W0.5p | gv -
119 Let say you have rotated gridA.grd and gridB.grd, restricting each
121 rotation to nodes inside polygons polyA.d and polyB.d, respectively,
122 using rotation A = (123W,22S,16,4) and rotation B = (108W, 16S, -14.5),
123 yielding rotated grids rot_gridA.grd and rot_gridB.grd. To determine
124 the region of overlap between the rotated grids, we use grdmath:
125 grdmath 1 rot_gridA.grd ISNAN SUB 1 rot_gridB.grd ISNAN SUB 2 EQ =
127 overlap.grd
128 The grid overlap.grd now has 1s in the regions of overlap and 0 else‐
130 where. You can use it as a mask or use grdcontour to extract a polygon
131 (contour).
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134 Data coordinates are assumed to be geodetic and will automatically be
135 converted to geocentric before spherical rotations are performed. We
136 convert back to geodetic coordinates for output. Note: If your data
137 already are geocentric, you can avoid the conversion by using --ELLIP‐
138 SOID=sphere.
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141 backtracker(1), grdspotter(1), hotspotter(1), originator(1) rotcon‐
142 verter(1)
143GMT 4.5.6 10 Mar 2011 GRDROTATER(1)