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PROGRAM:

NAME


grdrotater - Finite rotation reconstruction of geographic grid

SYNOPSIS


grdrotate ingrdfile rot_file|lon/lat/angle outgrdfile [ rotoutline ] [ polygonfile ] [ ]
[ region ] [ ] [ ages ] [ [level] ] [ -b<binary> ] [ -d<nodata> ] [ -h<headers> ] [
-i<flags> ] [ -n<flags> ] [ -:[i|o] ]

Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION


grdrotater reads a geographical grid and reconstructs it given total reconstruction
rotations. 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 reconstructed
region. The outlines of the reconstructed region is also returned provided the rotated
region is not the entire globe.

REQUIRED ARGUMENTS


ingrdfile
Name of a grid file in geographical (lon, lat) coordinates.

-Erotfile
Give file with rotation parameters. This file must contain one record for each
rotation; each record must be of the following format:

lon lat tstart [tstop] angle [ khat a b c d e f g df ]

where tstart and tstop are in Myr and lon lat angle are in degrees. tstart and
tstop are the ages of the old and young ends of a stage. If tstop is not present in
the record then a total reconstruction rotation is expected and tstop is implicitly
set to 0 and should not be specified for any of the records in the file. If a
covariance matrix C for the rotation is available it must be specified in a format
using the nine optional terms listed in brackets. Here, C = (g/khat)*[ a b d; b c
e; d e f ] which shows C made up of three row vectors. If the degrees of freedom
(df) in fitting the rotation is 0 or not given it is set to 10000. Blank lines and
records whose first column contains # will be ignored. You may prepend a leading +
to the filename to indicate you wish to invert the rotations. Alternative 1: Give
the filename composed of two plate IDs separated by a hyphen (e.g., PAC-MBL) and we
will instead extract that rotation from the GPlates rotation database. We return an
error if the rotation cannot be found. Alternative 2: Specify lon/lat/angle, i.e.,
the longitude, latitude, and opening angle (all in degrees and separated by /) for
a single total reconstruction rotation.

-Goutgrdfile
Name of output grid. This is the grid with the data reconstructed according to the
specified rotation. If more than one reconstruction time is implied then outgrdfile
must contain a C-format specifier to format a floating point number (reconstruction
time) to text.

OPTIONAL ARGUMENTS


-Drotoutline
Name of the grid polygon outline file. This represents the outline of the grid
reconstructed to the specified time. If more than one reconstruction time is
implied then rotoutline must contain a C-format specifier to format a floating
point number (reconstruction time) to text. If only one time is implied and -D is
not set then we write the polygon to stdout (but see -N).

-Fpolygonfile
Specify a multisegment closed polygon file that describes the inside area of the
grid that should be projected [Default projects entire grid].

-N Do Not output the rotated polygon outline [Default will write it to stdout, or to a
file via -D].

-R[unit]west/east/south/north[/zmin/zmax][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 for grid creation, give
Rcodelon/lat/nx/ny, where code is a 2-character combination of L, C, R (for left,
center, or right) and T, M, B for top, middle, or bottom. e.g., BL for lower left.
This indicates which point on a rectangular region the lon/lat coordinate refers
to, and the grid dimensions nx and ny with grid spacings via -I is used to create
the corresponding region. Alternatively, specify the name of an existing grid file
and the -R settings (and grid spacing, if applicable) are copied from the grid.
Using -Runit expects projected (Cartesian) coordinates compatible with chosen -J
and we inversely project to determine actual rectangular geographic region. For
perspective view (-p), optionally append /zmin/zmax. In case of perspective view
(-p), a z-range (zmin, zmax) can be appended to indicate the third dimension. This
needs to be done only when using the -Jz option, not when using only the -p option.
In the latter case a perspective view of the plane is plotted, with no third
dimension.

-S Skip the rotation of the grid, just rotate the polygon outline (requires -F if no
grid is provided).

-Tages Sets the desired reconstruction times. For a single time append the desired time.
For an equidistant range of reconstruction times give -Tstart/stop/inc or
-Tstart/stop/npoints+. For an non-equidistant set of reconstruction times please
pass them via the first column in a file, e.g., -Tagefile. If no -T option is
given and -E specified a rotation file then we equate the rotation file times with
the reconstruction times.

-V[level] (more ...)
Select verbosity level [c].

-bi[ncols][t] (more ...)
Select native binary input. [Default is 2 input columns].

-bo[ncols][type] (more ...)
Select native binary output. [Default is same as input].

-d[i|o]nodata (more ...)
Replace input columns that equal nodata with NaN and do the reverse on output.

-h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
Skip or produce header record(s).

-:[i|o] (more ...)
Swap 1st and 2nd column on input and/or output.

-icols[l][sscale][ooffset][,...] (more ...)
Select input columns (0 is first column).

-n[b|c|l|n][+a][+bBC][+c][+tthreshold] (more ...)
Select interpolation mode for grids.

-^ or just -
Print a short message about the syntax of the command, then exits (NOTE: on Windows
use just -).

-+ or just +
Print an extensive usage (help) message, including the explanation of any
module-specific option (but not the GMT common options), then exits.

-? or no arguments
Print a complete usage (help) message, including the explanation of options, then
exits.

--version
Print GMT version and exit.

--show-datadir
Print full path to GMT share directory and exit.

CONSEQUENCES OF GRID RESAMPLING


Resample or sampling of grids will use various algorithms (see -n) that may lead to
possible distortions or unexpected results in the resampled values. One expected effect
of resampling with splines is the tendency for the new resampled values to slightly exceed
the global min/max limits of the original grid. If this is unacceptable, you can impose
clipping of the resampled values values so they do not exceed the input min/max values by
adding +c to your -n option.

GEODETIC VERSUS GEOCENTRIC COORDIINATES


All spherical rotations are applied to geocentric coordinates. This means that incoming
data points and grids are considered to represent geodetic coordinates and must first be
converted to geocentric coordinates. Rotations are then applied, and the final
reconstructed points are converted back to geodetic coordinates. This default behavior
can be bypassed if the ellipsoid setting PROJ_ELLIPSOID is changed to Sphere.

EXAMPLES


To rotate the data defined by grid topo.nc and the polygon outline clip_path.d, using a
total reconstruction rotation with pole at (135.5, -33.0) and a rotation angle of 37.3
degrees and bicubic interpolation, try

gmt grdrotater topo.nc -E135.5/-33/37.3 -V -Fclip_path.d -Grot_topo.nc > rot_clip_path.d

To rotate the entire grid faa.nc back to 32 Ma using the rotation file rotations.txt and a
bilinear interpolation, try

gmt grdrotater faa.nc -Erotations.txt -T32 -V -Grot_faa.nc -nl > rot_faa_path.d

To just see how the outline of the grid large.nc will plot after the same rotation, try

gmt grdrotater large.nc -Erotations.txt -T32 -V -S \| psxy -Rg -JH180/6i -B30 -W0.5p \| gv -

To rotate the grid topo.nc back to 100 Ma using the rotation file rotations.txt and
request a reconstruction every 10 Myr, saving both grids and outlines to filenames that
derive from templates, try

gmt grdrotater topo.nc -Erotations.txt -T10/100/10 -V -Grot_topo_%g.nc -Drot_topo_path_%g.d

Let say you have rotated gridA.nc and gridB.nc, 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.nc and rot_gridB.nc. To
determine the region of overlap between the rotated grids, we use grdmath:

gmt grdmath 1 rot_gridA.nc ISNAN SUB 1 rot_gridB.nc ISNAN SUB 2 EQ = overlap.nc

The grid overlap.nc now has 1s in the regions of overlap and 0 elsewhere. You can use it
as a mask or use grdcontour -D to extract a polygon (i.e., a contour).

NOTES


GMT distributes the EarthByte rotation model Global_EarthByte_230-0Ma_GK07_AREPS.rot. To
use an alternate rotation file, create an environmental parameters named GPLATES_ROTATIONS
that points to an alternate rotation file.

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