Provided by: gmt-common_5.2.1+dfsg-3build1_all 
NAME
grdspotter - Create CVA image from a gravity or topography grid
SYNOPSIS
grdspotter [grdfile] rotfile CVAgrid increment region [ agegrid ] [ DIgrid ] [ IDgrid ] [ ] [ upper_age
] [ PAgrid ] [ IDinfo ] [ ] [ t|ufixed_val ] [ [ [level] ] [ n_try ]] [ -Zz_min[/z_max[/z_inc]] ] [ -r ]
Note: No space is allowed between the option flag and the associated arguments.
DESCRIPTION
grdspotter reads a grid file with residual bathymetry or gravity and calculates flowlines from each node
that exceeds a minimum value using the specified rotations file. These flowlines are then convolved with
the volume of the prism represented by each grid node and added up to give a Cumulative Volcano Amplitude
grid (CVA).
REQUIRED ARGUMENTS
grdfile
Data grid to be processed, typically residual bathymetry or free-air anomalies.
-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. Alternatively, 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.
-G Specify name for output CVA grid file.
-Ixinc[unit][=|+][/yinc[unit][=|+]]
x_inc [and optionally y_inc] is the grid spacing. Optionally, append a suffix modifier.
Geographical (degrees) coordinates: Append m to indicate arc minutes or s to indicate arc seconds.
If one of the units e, f, k, M, n or u is appended instead, the increment is assumed to be given
in meter, foot, km, Mile, nautical mile or US survey foot, respectively, and will be converted to
the equivalent degrees longitude at the middle latitude of the region (the conversion depends on
PROJ_ELLIPSOID). If /y_inc is given but set to 0 it will be reset equal to x_inc; otherwise it
will be converted to degrees latitude. All coordinates: If = is appended then the corresponding
max x (east) or y (north) may be slightly adjusted to fit exactly the given increment [by default
the increment may be adjusted slightly to fit the given domain]. Finally, instead of giving an
increment you may specify the number of nodes desired by appending + to the supplied integer
argument; the increment is then recalculated from the number of nodes and the domain. The
resulting increment value depends on whether you have selected a gridline-registered or
pixel-registered grid; see App-file-formats for details. Note: if -Rgrdfile is used then the grid
spacing has already been initialized; use -I to override the values.
-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.
OPTIONAL ARGUMENTS
-Aagegrid
Supply a crustal age grid that is co-registered with the input data grid. These ages become the
upper ages to use when constructing flowlines [Default extend flowlines back to oldest age found
in the rotation file; but see ].
-DDIgrid
Use flowlines to determine the maximum CVA encountered along each flowline and create a Data
Importance (DI) grid with these values at the originating nodes.
-LIDgrid
Supply a co-registered grid with seamount chain IDs for each node. This option requires that you
also use .
-M Do not attempt to keep all flowlines in memory when using -D and/or -P. Should you run out of
memory you can use this option to compute flowlines on-the-fly. It will be slower as we no longer
can reuse the flowlines calculated for the CVA step. Cannot be used with -W or the multi-slice
mode in -Z.
-Nupper_age
Set the upper age to assign to nodes whose crustal age is unknown (i.e., NaN) [no upper age]. Also
see .
-PPAgrid
Use flowlines to determine the flowline age at the CVA maximum for each node and create a
Predicted Age (PA) grid with these values at the originating nodes.
-QIDinfo
Either give (1) a single ID to use or (2) the name of a file with a list of IDs to use [Default
uses all IDs]. Each line would be TAG ID [w e s n]. The w/e/s/n zoom box is optional; if specified
it means we only trace the flowline if inside this region [Default uses region set by -R].
Requires -L.
-S Normalize the resulting CVA grid to percentages of the CVA maximum. This also normalizes the DI
grid (if requested).
-Tt|ufixed_val
Selects ways to adjust ages; repeatable. Choose from -Tt to truncate crustal ages given via the
option that exceed the upper age set with [no truncation], or ufixed_val which means that after a
node passes the test implied by , we use this fixed_val instead in the calculations. [Default uses
individual node values].
-V[level] (more ...)
Select verbosity level [c].
-Wn_try
Get n_try bootstrap estimates of the maximum CVA location; the longitude and latitude results are
written to stdout [Default is no bootstrapping]. Cannot be used with -M.
-Zz_min[/z_max[/z_inc]]
Ignore nodes with z-values lower than z_min [0] and optionally larger than z_max [Inf]. Give
z_min/z_max/z_inc to make separate CVA grids for each z-slice [Default makes one CVA grid].
Multi-slicing cannot be used with -M.
-r (more ...)
Set pixel node registration [gridline].
-^ 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.
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 create a CVA image from the Pacific topography grid Pac_res_topo.nc, using the DC85.d Euler poles, and
only output a grid for the specified domain, run
gmt grdspotter Pac_res_topo.nc -EDC85.d -GCVA.nc -R190/220/15/25 -I2m -N145 -Tt -V
This file can then be plotted with grdimage.
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.
SEE ALSO
gmt, grdimage, project, mapproject, backtracker, hotspotter, originator
REFERENCES
Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80 (29), p. 319.
Wessel, P., 2008, Hotspotting: Principles and properties of a plate tectonic Hough transform, Geochem.
Geophys. Geosyst. 9(Q08004): doi:10.1029/2008GC002058.
COPYRIGHT
2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.2.1 January 28, 2016 GRDSPOTTER(1gmt)