Provided by: gmt_4.5.11-1build1_amd64 bug


       grdrotater - Rotate a grid using a finite rotation


       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] ]


       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.

              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[][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

       -:     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.


       backtracker(1), grdspotter(1), hotspotter(1), originator(1) rotconverter(1)