|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.|
-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.
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).
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.
|GMT 4.5.14||GRDROTATER (1)||1 Nov 2015|