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)