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 0.5
p
| 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)