Ubuntu Manpage: grdspotter - Create CVA image from a gravity or topography grid

Provided by: gmt-common_5.4.3+dfsg-1_all

NAME

       grdspotter - Create CVA image from a gravity or topography grid

SYNOPSIS

       grdspotter [grdfile]  -Erotfile  -GCVAgrid
        -Iincrement
        -Rregion [  -Aagegrid ] [  -DDIgrid ] [  -LIDgrid ] [  -M ] [  -Nupper_age ] [  -PPAgrid ] [  -QIDinfo ]
       [  -S ] [  -Tt|ufixed_val ] [ [  -V[level] ] [  -Wn_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][+e|n][/yinc[unit][+e|n]]
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 +e 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 +n 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.

-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 [±]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 (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  -N].

       -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  -Q.

       -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  -A.

       -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
              -A option that exceed the upper age set with  -N [no truncation],  or   -Tufixed_val  which  means
              that  after  a  node  passes  the  test  implied  by   -Z,  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 just use -).

       -+ 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 all options, then exits.

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.

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

       2018, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe

5.4.3                                             Jan 03, 2018                                  GRDSPOTTER(1gmt)