manpagez: man pages & more
man grdspotter(1)
Home | html | info | man
grdspotter(1)                         GMT                        grdspotter(1)




NAME

       grdspotter - Create CVA image from a gravity or topography grid


SYNOPSIS

       grdspotter [grdfile]  -Erotfile  -GCVAgrid
        -Iincrement
        -Rregion  [   -Aagegrid ] [  -DDIgrid ] [  -LIDgrid ] [  -M ] [  -Nup-
       per_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  rota-
              tion 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, nau-
              tical mile or US survey foot, respectively,  and  will  be  con-
              verted  to  the equivalent degrees longitude at the middle lati-
              tude 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  coordi-
              nates:  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  recalcu-
              lated  from  the  number  of nodes and the domain. The resulting
              increment value depends on whether you  have  selected  a  grid-
              line-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
              [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.


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  con-
              structing 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. Can-
              not 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 maxi-
              mum.  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 indi-
              vidual node values].

       -V[level] (more a|)
              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 a|)
              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  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.


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 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_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

       gmt(1), grdimage(1), project(1), mapproject(1), backtracker(1),
       gmtpmodeler(1), grdpmodeler(1), grdrotater(1), hotspotter(1),
       originator(1)


REFERENCES

       Wessel,  P.,  1999,  aHotspottinga  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

       2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe



5.4.2                            Jun 24, 2017                    grdspotter(1)

gmt5 5.4.2 - Generated Thu Jun 29 08:28:47 CDT 2017
© manpagez.com 2000-2021
Individual documents may contain additional copyright information.