grdrotater(1) GMT grdrotater(1)
NAME
grdrotater - Finite rotation reconstruction of geographic grid
SYNOPSIS
grdrotater ingrdfile -Erot_file|lon/lat/angle
-Goutgrdfile [ -Drotoutline ] [ -Fpolygonfile ] [ -N ] [ -Rregion
] [ -S ] [ -Tages ] [ -V[level] ] [ -bbinary ] [ -dnodata ] [
-hheaders ] [ -nflags ] [ -:[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 rota-
tion 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 recon-
structed 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 (recon-
struction time) to text.
OPTIONAL ARGUMENTS
-Drotoutline
Name of the grid polygon outline file. This represents the out-
line 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].
-Rwest/east/south/north[/zmin/zmax][+r][+uunit]
west, east, south, and north specify the region of interest, and
you may specify them in decimal degrees or in
[A+-]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. Appending +uunit expects projected (Carte-
sian) 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 rota-
tion file times with the reconstruction times.
-V[level] (more a|)
Select verbosity level [c].
-bi[ncols][t] (more a|)
Select native binary input. [Default is 2 input columns].
-bo[ncols][type] (more a|)
Select native binary output. [Default is same as input].
-d[i|o]nodata (more a|)
Replace input columns that equal nodata with NaN and do the
reverse on output.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more a|)
Skip or produce header record(s).
-:[i|o] (more a|)
Swap 1st and 2nd column on input and/or output.
-n[b|c|l|n][+a][+bBC][+c][+tthreshold] (more a|)
Select interpolation mode for grids.
-^ or just -
Print a short message about the syntax of the command, then
exits (NOTE: on Windows just use -).
-+ or just +
Print an extensive usage (help) message, including the explana-
tion 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 all options, then exits.
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 lim-
its 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 coordi-
nates. 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 rota-
tions.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 rota-
tion 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 else-
where. You can use it as a mask or use grdcontour -D to extract a poly-
gon (i.e., a contour).
NOTES
GMT distributes the EarthByte rotation model Global_Earth-
Byte_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.
SEE ALSO
backtracker(1), grdcontour(1), gmtpmodeler(1), grdmath(1),
grdpmodeler(1), grdspotter(1), hotspotter(1), originator(1),
rotconverter(1)
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 grdrotater(1)
gmt5 5.4.2 - Generated Thu Jun 29 08:07:46 CDT 2017