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       grdspotter - Create CVA image directly from gravity or bathymetry grids


       grdspotter   [grdfile]   -Erotations_file   -GCVAgrid  -Ixinc[unit][=|+][/yinc[unit][=|+]]
       -Rwest/east/south/north[r] [ -Aagegrid ] [ -Bn_try ] [ -C ] [ -DDIgrid  ]  [  -F  ]  [  -L
       IT(IDgrid)  ] [ -M ] [ -Nupper_age ] [ -PPAgrid ] [ -QIDinfo ] [ -S ] [ -T ] [ -Ufixed_val
       ] [ -V ] [ -Zz_min[/z_max[/z_inc]] ]


       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).
            No  space  between  the option flag and the associated arguments.  Use upper case for
       the option flags and lower case for modifiers.

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

       -E     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 -C is set then a total
              reconstruction rotation is expected and tstop is implicitly set to 0 and should not
              be specified 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

       -G     Specify name for output CVA grid file.

       -I     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
              c  to indicate arc seconds.  If one of the units e, k, i, or n is appended instead,
              the increment is assumed to be given  in  meter,  km,  miles,  or  nautical  miles,
              respectively,  and  will  be  converted  to the equivalent degrees longitude at the
              middle latitude of the region (the conversion depends on 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
              Appendix  B  for details.  Note: if -Rgrdfile is used then grid spacing has already
              been initialized; use -I to override the values.

       -R     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,  specify  the  name  of  an
              existing grid file and the -R settings (and grid spacing, if applicable) are copied
              from the grid.


       -A     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].

       -B     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.

       -C     Expect  Total  Reconstruction  Rotations  rather  than  Forward   Stage   Rotations
              [Default].   File format is similar to the stage pole format except that the tstart
              column is not present (assumed to be 0 Ma).

       -D     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.

       -F     Force pixel registration [Default is grid registration].

       -L     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 -B or the multi-slice mode in -Z.

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

       -P     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.

       -Q     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).

       -T     Truncate crustal ages given via the -A option that exceed the upper age set with -N
              [no truncation].

       -U     After a node passes the test implied by -Z,  use  this  fixed_val  instead  in  the
              calculations.  [Default uses individual node values].

       -V     Selects  verbose  mode,  which  will  send progress reports to stderr [Default runs

       -Z     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.


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

       grdspotter Pac_res_topo.grd -E DC85.d -G CVA.grd -R 190/220/15/25 -I 2m -N 145 -T -V

       This file can then be plotted with grdimage.


       Data  coordinates  are  assumed  to  be  geodetic  and  will automatically be converted to
       geocentric before  spherical  rotations  are  performed.   We  convert  back  to  geodetic
       coordinates  for  output.   Note:  If  your data already are geocentric, you can avoid the
       conversion by using --ELLIPSOID=sphere.


       GMT(1),   grdimage(1),   grdrotater(1),   project(1),    mapproject(1),    backtracker(1),
       hotspotter(1), originator(1)


       Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80 (29), p. 319.