Provided by: gmt-common_5.4.5+dfsg-2_all bug


       grdspotter - Create CVA image from a gravity or topography grid


       grdspotter [grdfile]  -Erotfile  -GCVAgrid
        -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.


       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).


              Data grid to be processed, typically residual bathymetry or free-air anomalies.

              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.

              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.

              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 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


              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].

              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.

              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.

              Set  the  upper age to assign to nodes whose crustal age is unknown (i.e., NaN) [no
              upper age]. Also see  -A.

              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.

              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).

              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].

              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.

              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.


       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.


       To  create  a CVA image from the Pacific topography grid, using the DC85.d
       Euler poles, and only output a grid for the specified domain, run

              gmt grdspotter -EDC85.d -R190/220/15/25 -I2m -N145 -Tt -V

       This file can then be plotted with grdimage.


       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.


       gmt, grdimage, project, mapproject,  backtracker,  gmtpmodeler,  grdpmodeler,  grdrotater,
       hotspotter, originator


       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.


       2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe