Provided by: gmt_4.5.11-1build1_amd64 
NAME
grdrotater - Rotate a grid using a finite rotation
SYNOPSIS
grdrotate ingrdfile -Goutgrdfile -Tplon/plat/omega [ -Fpolygonfile ] [ -H[i][nrec] ] [ -N
] [ -Q[b|c|l|n][[/]threshold] ] [ -Rwest/east/south/north[r] ] [ -S ] [ -V ] [ -:[i|o] ] [
-b[i|o][s|S|d|D[ncol]|c[var1/...]] ] [ -m[flag] ]
DESCRIPTION
grdrotater reads a geographical grid and reconstructs it given a total reconstruction
rotation. Optionally, the user may supply a clipping polygon in multiple-segment format;
then, only the part of the grid inside the polygon is used to determine the return grid
region. The outline of the projected region is returned on stdout provided the rotated
region is not the entire globe.
No space between the option flag and the associated arguments. Use upper case for
the option flags and lower case for modifiers.
ingrdfile
Name of a grid file in geographical (lon, lat) coordinates.
-G Name of output grid. This is the grid with the data reconstructed according to the
specified rotation.
-T Finite rotation. Specify the longitude and latitude of the rotation pole and the
opening angle, all in degrees.
OPTIONS
-F Specify a multi-segment closed polygon file that describes the inside area of the
grid that should be projected [Default projects entire grid].
-H Input file(s) has header record(s). If used, the default number of header records
is N_HEADER_RECS. Use -Hi if only input data should have header records [Default
will write out header records if the input data have them]. Blank lines and lines
starting with # are always skipped.
-N Do Not output the rotated polygon outline [Default will write it to stdout].
-Q Quick mode, use bilinear rather than bicubic interpolation [Default].
Alternatively, select the interpolation mode by adding b for B-spline smoothing, c
for bicubic interpolation, l for bilinear interpolation or n for nearest-neighbor
value. Optionally, append threshold in the range [0,1]. This parameter controls
how close to nodes with NaN values the interpolation will go. E.g., a threshold of
0.5 will interpolate about half way from a non-NaN to a NaN node, whereas 0.1 will
go about 90% of the way, etc. [Default is 1, which means none of the (4 or 16)
nearby nodes may be NaN]. -Q0 will just return the value of the nearest node
instead of interpolating. This is the same as using -Qn.
-R west, east, south, and north specify the Region of interest, and you may specify
them in decimal degrees or in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if
lower left and upper right map coordinates are given instead of w/e/s/n. The two
shorthands -Rg and -Rd stand for global domain (0/360 and -180/+180 in longitude
respectively, with -90/+90 in latitude). Alternatively, specify the name of an
existing grid file and the -R settings (and grid spacing, if applicable) are copied
from the grid.
-S Skip the rotation of the grid, just rotate the polygon outline (requires -F).
-V Selects verbose mode, which will send progress reports to stderr [Default runs
"silently"].
-: Toggles between (longitude,latitude) and (latitude,longitude) input/output.
[Default is (longitude,latitude)].
-bi Selects binary input. Append s for single precision [Default is d (double)].
Uppercase S or D will force byte-swapping. Optionally, append ncol, the number of
columns in your binary input file if it exceeds the columns needed by the program.
Or append c if the input file is netCDF. Optionally, append var1/var2/... to
specify the variables to be read. [Default is 2 input columns].
-bo Selects binary output. Append s for single precision [Default is d (double)].
Uppercase S or D will force byte-swapping. Optionally, append ncol, the number of
desired columns in your binary output file. [Default is same as input].
-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 -b must set the number of output columns explicitly. By
default the -m setting applies to both input and output. Use -mi and -mo to give
separate settings to input and output.
EXAMPLES
To rotate the data defined by grid topo.grd and the polygon outline clip_path.d, using a
finite rotation with pole at (135.5, -33.0) and a rotation angle of 37.3 degrees and
bicubic interpolation, try
grdrotater topo.grd -T 135.5/-33/37.3 -V -F clip_path.d -G rot_topo.grd > rot_clip_path.d
To rotate the entire grid faa.grd using a finite rotation pole at (67:45W, 22:35S) and a
rotation angle of 19.6 degrees using a bilinear interpolation, try
grdrotater faa.grd -T 67:45W/22:35S/19.6 -V -Q -G rot_faa.grd > rot_faa_path.d
To just see how the outline of the grid large.grd will plot after the same rotation, try
grdrotater large.grd -T 67:45W/22:35S/19.6 -V -S | psxy -Rg -JH 180/6i -B 30 -m -W 0.5p |
gv -
Let say you have rotated gridA.grd and gridB.grd, restricting each rotation to nodes
inside polygons polyA.d and polyB.d, respectively, using rotation A = (123W,22S,16,4) and
rotation B = (108W, 16S, -14.5), yielding rotated grids rot_gridA.grd and rot_gridB.grd.
To determine the region of overlap between the rotated grids, we use grdmath:
grdmath 1 rot_gridA.grd ISNAN SUB 1 rot_gridB.grd ISNAN SUB 2 EQ = overlap.grd
The grid overlap.grd now has 1s in the regions of overlap and 0 elsewhere. You can use it
as a mask or use grdcontour to extract a polygon (contour).
COORDINATES
Data coordinates are assumed to be geodetic and will automatically be converted to
geocentric before spherical rotations are performed. We convert back to geodetic
coordinates for output. Note: If your data already are geocentric, you can avoid the
conversion by using --ELLIPSOID=sphere.
SEE ALSO
backtracker(1), grdspotter(1), hotspotter(1), originator(1) rotconverter(1)