.TH GRDSPOTTER 1gmt "Feb 27 2014" "GMT 4.5.13 (SVN)" "Generic Mapping Tools"
.SH NAME
grdspotter \- Create CVA image directly from gravity or bathymetry grids 
.SH SYNOPSIS
\fBgrdspotter\fP [\fIgrdfile\fP] \fB\-E\fP\fIrotations_file\fP 
\fB\-G\fP\fICVAgrid\fP \fB\-I\fP\fIxinc\fP[\fIunit\fP][\fB=\fP|\fB+\fP][/\fIyinc\fP[\fIunit\fP][\fB=\fP|\fB+\fP]] 
\fB\-R\fP\fIwest\fP/\fIeast\fP/\fIsouth\fP/\fInorth\fP[\fBr\fP] [ \fB\-A\fP\fIagegrid\fP ] [ \fB\-B\fP\fIn_try\fP ] [ \fB\-C\fP ] [ \fB\-D\fP\fIDIgrid\fP ] [ \fB\-F\fP ] 
[ \fB\-L\fP IT(IDgrid) ] [ \fB\-M\fP ] [ \fB\-N\fP\fIupper_age\fP ] [ \fB\-P\fP\fIPAgrid\fP ] [ \fB\-Q\fP\fIIDinfo\fP ] [ \fB\-S\fP ] 
[ \fB\-T\fP ] [ \fB\-U\fP\fIfixed_val\fP ] [ \fB\-V\fP ] [ \fB\-Z\fP\fIz_min\fP[/\fIz_max\fP[/\fIz_inc\fP]] ]
.SH DESCRIPTION
\fBgrdspotter\fP 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).
.br
	No space between the option flag and the associated arguments.  Use upper case for the
option flags and lower case for modifiers.
.TP
\fIgrdfile\fP
Data grid to be processed, typically residual bathymetry or free-air anomalies.
.TP
\fB\-E\fP
Give file with rotation parameters.  This file must contain
one record for each rotation; each record must be of the following format:
.br
.sp
	\fIlon lat tstart [tstop] angle\fP [ \fIkhat a b c d e f g df\fP ]
.br
.sp
where \fItstart\fP and \fItstop\fP are in Myr and \fIlon lat angle\fP are in degrees.
\fItstart\fP and \fItstop\fP are the ages of the old and young ends of a stage.  If \fB\-C\fP is set then a total
reconstruction rotation is expected and \fItstop\fP is implicitly set to 0 and
should not be specified in the file.  If a covariance matrix \fBC\fP for the rotation is available
it must be specified in a format using the nine optional terms listed in brackets.
Here, \fBC\fP = (\fIg\fP/\fIkhat\fP)*[ \fIa b d; b c e; d e f\fP ] which shows \fBC\fP
made up of three row vectors.
If the degrees of freedom (\fIdf\fP) 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.
.TP
\fB\-G\fP
Specify name for output CVA grid file.
.TP
\fB\-I\fP
\fIx_inc\fP [and optionally \fIy_inc\fP] is the grid spacing. Optionally, append a suffix
modifier.  \fBGeographical (degrees) coordinates\fP: Append \fBm\fP to
indicate arc minutes or \fBc\fP to indicate arc seconds.  If one of the units \fBe\fP, \fBk\fP, \fBi\fP,
or \fBn\fP 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 \fBELLIPSOID\fP).  If /\fIy_inc\fP is given but set to 0 it will be reset equal to
\fIx_inc\fP; otherwise it will be converted to degrees latitude.  
\fBAll coordinates\fP: If \fB=\fP is appended then
the corresponding max \fIx\fP (\fIeast\fP) or \fIy\fP (\fInorth\fP) 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 \fInumber of nodes\fP desired by appending \fB+\fP 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 \fB\-R\fP\fIgrdfile\fP is used then
grid spacing has already been initialized; use \fB\-I\fP to override the values.
.TP
\fB\-R\fP
\fIwest, east, south,\fP and \fInorth\fP 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 \fBr\fP if lower left and upper right
map coordinates are given instead of w/e/s/n.  The two shorthands \fB\-Rg\fP and \fB\-Rd\fP 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 \fB\-R\fP settings (and grid spacing, if applicable) are copied from the grid.
.SH OPTIONS
.TP
\fB\-A\fP
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 \fB\-N\fP].
.TP
\fB\-B\fP
Get \fIn_try\fP bootstrap estimates of the maximum CVA location; the longitude and latitude
results are written to stdout [Default is no bootstrapping].  Cannot be used with \fB\-M\fP.
.TP
\fB\-C\fP
Expect Total Reconstruction Rotations rather than Forward Stage Rotations [Default].
File format is similar to the stage pole format except that the \fItstart\fP column
is not present (assumed to be 0 Ma).
.TP
\fB\-D\fP
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.
.TP
\fB\-F\fP
Force pixel registration [Default is grid registration].
.TP
\fB\-L\fP
Supply a co-registered grid with seamount chain IDs for each node.  This option requires that
you also use \fB\-Q\fP.
.TP
\fB\-M\fP
Do not attempt to keep all flowlines in memory when using \fB\-D\fP and/or \fB\-P\fP.  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 \fB\-B\fP or the
multi-slice mode in \fB\-Z\fP.
.TP
\fB\-N\fP
Set the upper age to assign to nodes whose crustal age is unknown (i.e., NaN) [no upper age].
Also see \fB\-A\fP.
.TP
\fB\-P\fP
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.
.TP
\fB\-Q\fP
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 \fIw/e/s/n\fP zoom box is optional; if specified it means
we only trace the flowline if inside this region [Default uses region set by \fB\-R\fP].  Requires \fB\-L\fP.
.TP
\fB\-S\fP
Normalize the resulting CVA grid to percentages of the CVA maximum.  This also normalizes the DI grid (if requested).
.TP
\fB\-T\fP
Truncate crustal ages given via the \fB\-A\fP option that exceed the upper age set with \fB\-N\fP [no truncation].
.TP
\fB\-U\fP
After a node passes the test implied by \fB\-Z\fP, use this \fIfixed_val\fP instead in the calculations.
[Default uses individual node values].
.TP
\fB\-V\fP
Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].
.TP
\fB\-Z\fP
Ignore nodes with z-values lower than \fIz_min\fP [0] and optionally larger than \fIz_max\fP [Inf].
Give \fIz_min/z_max/z_inc\fP to make separate CVA grids for each \fIz\fP-slice [Default makes one CVA grid].
Multi-slicing cannot be used with \fB\-M\fP.
.SH EXAMPLES
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
.br
.sp
\fBgrdspotter\fP Pac_res_topo.grd \fB\-E\fP DC85.d \fB\-G\fP CVA.grd \fB\-R\fP 190/220/15/25 \fB\-I\fP 2\fBm\fP \fB\-N\fP 145 \fB\-T\fP \fB\-V\fP
.br
.sp
This file can then be plotted with \fBgrdimage\fP.
.SH COORDINATES
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.
.SH "SEE ALSO"
.IR GMT (1),
.IR grdimage (1),
.IR grdrotater (1),
.IR project (1),
.IR mapproject (1),
.IR backtracker (1),
.IR hotspotter (1),
.IR originator (1)
.SH REFERENCES
Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80 (29), p. 319.
.br