1GRDSPOTTER(1) GMT GRDSPOTTER(1)
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6 grdspotter - Create CVA image from a gravity or topography grid
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9 grdspotter [grdfile] -Erotfile -GCVAgrid
10 -Iincrement
11 -Rregion [ -Aagegrid ] [ -DDIgrid ] [ -LIDgrid ] [ -M ] [ -Nup‐
12 per_age ] [ -PPAgrid ] [ -QIDinfo ] [ -S ] [ -Tt|ufixed_val ] [ [
13 -V[level] ] [ -Wn_try ]] [ -Zz_min[/z_max[/z_inc]] ] [ -r ]
14 Note: No space is allowed between the option flag and the associated
16 arguments.
17
19 grdspotter reads a grid file with residual bathymetry or gravity and
20 calculates flowlines from each node that exceeds a minimum value using
21 the specified rotations file. These flowlines are then convolved with
22 the volume of the prism represented by each grid node and added up to
23 give a Cumulative Volcano Amplitude grid (CVA).
24
26 grdfile
27 Data grid to be processed, typically residual bathymetry or
28 free-air anomalies.
29 -Erotfile
31 Give file with rotation parameters. This file must contain one
32 record for each rotation; each record must be of the following
33 format:
34 lon lat tstart [tstop] angle [ khat a b c d e f g df ]
36 where tstart and tstop are in Myr and lon lat angle are in
38 degrees. tstart and tstop are the ages of the old and young ends
39 of a stage. If tstop is not present in the record then a total
40 reconstruction rotation is expected and tstop is implicitly set
41 to 0 and should not be specified for any of the records in the
42 file. If a covariance matrix C for the rotation is available it
43 must be specified in a format using the nine optional terms
44 listed in brackets. Here, C = (g/khat)*[ a b d; b c e; d e f ]
45 which shows C made up of three row vectors. If the degrees of
46 freedom (df) in fitting the rotation is 0 or not given it is set
47 to 10000. Blank lines and records whose first column contains #
48 will be ignored. You may prepend a leading + to the filename to
49 indicate you wish to invert the rotations. Alternatively, give
50 the filename composed of two plate IDs separated by a hyphen
51 (e.g., PAC-MBL) and we will instead extract that rotation from
52 the GPlates rotation database. We return an error if the rota‐
53 tion cannot be found.
54 -G Specify name for output CVA grid file.
56 -Ixinc[unit][+e|n][/yinc[unit][+e|n]]
58 x_inc [and optionally y_inc] is the grid spacing. Optionally,
59 append a suffix modifier. Geographical (degrees) coordinates:
60 Append m to indicate arc minutes or s to indicate arc seconds.
61 If one of the units e, f, k, M, n or u is appended instead, the
62 increment is assumed to be given in meter, foot, km, Mile, nau‐
63 tical mile or US survey foot, respectively, and will be con‐
64 verted to the equivalent degrees longitude at the middle lati‐
65 tude of the region (the conversion depends on PROJ_ELLIPSOID).
66 If y_inc is given but set to 0 it will be reset equal to x_inc;
67 otherwise it will be converted to degrees latitude. All coordi‐
68 nates: If +e is appended then the corresponding max x (east) or
69 y (north) may be slightly adjusted to fit exactly the given
70 increment [by default the increment may be adjusted slightly to
71 fit the given domain]. Finally, instead of giving an increment
72 you may specify the number of nodes desired by appending +n to
73 the supplied integer argument; the increment is then recalcu‐
74 lated from the number of nodes and the domain. The resulting
75 increment value depends on whether you have selected a grid‐
76 line-registered or pixel-registered grid; see App-file-formats
77 for details. Note: if -Rgrdfile is used then the grid spacing
78 has already been initialized; use -I to override the values.
79 -Rwest/east/south/north[/zmin/zmax][+r][+uunit]
81 west, east, south, and north specify the region of interest, and
82 you may specify them in decimal degrees or in
83 [±]dd:mm[:ss.xxx][W|E|S|N] format Append +r if lower left and
84 upper right map coordinates are given instead of w/e/s/n. The
85 two shorthands -Rg and -Rd stand for global domain (0/360 and
86 -180/+180 in longitude respectively, with -90/+90 in latitude).
87 Alternatively for grid creation, give Rcodelon/lat/nx/ny, where
88 code is a 2-character combination of L, C, R (for left, center,
89 or right) and T, M, B for top, middle, or bottom. e.g., BL for
90 lower left. This indicates which point on a rectangular region
91 the lon/lat coordinate refers to, and the grid dimensions nx and
92 ny with grid spacings via -I is used to create the corresponding
93 region. Alternatively, specify the name of an existing grid
94 file and the -R settings (and grid spacing, if applicable) are
95 copied from the grid. Appending +uunit expects projected (Carte‐
96 sian) coordinates compatible with chosen -J and we inversely
97 project to determine actual rectangular geographic region. For
98 perspective view (-p), optionally append /zmin/zmax. In case of
99 perspective view (-p), a z-range (zmin, zmax) can be appended to
100 indicate the third dimension. This needs to be done only when
101 using the -Jz option, not when using only the -p option. In the
102 latter case a perspective view of the plane is plotted, with no
103 third dimension.
104
106 -Aagegrid
107 Supply a crustal age grid that is co-registered with the input
108 data grid. These ages become the upper ages to use when con‐
109 structing flowlines [Default extend flowlines back to oldest age
110 found in the rotation file; but see -N].
111 -DDIgrid
113 Use flowlines to determine the maximum CVA encountered along
114 each flowline and create a Data Importance (DI) grid with these
115 values at the originating nodes.
116 -LIDgrid
118 Supply a co-registered grid with seamount chain IDs for each
119 node. This option requires that you also use -Q.
120 -M Do not attempt to keep all flowlines in memory when using -D
122 and/or -P. Should you run out of memory you can use this option
123 to compute flowlines on-the-fly. It will be slower as we no
124 longer can reuse the flowlines calculated for the CVA step. Can‐
125 not be used with -W or the multi-slice mode in -Z.
126 -Nupper_age
128 Set the upper age to assign to nodes whose crustal age is
129 unknown (i.e., NaN) [no upper age]. Also see -A.
130 -PPAgrid
132 Use flowlines to determine the flowline age at the CVA maximum
133 for each node and create a Predicted Age (PA) grid with these
134 values at the originating nodes.
135 -QIDinfo
137 Either give (1) a single ID to use or (2) the name of a file
138 with a list of IDs to use [Default uses all IDs]. Each line
139 would be TAG ID [w e s n]. The w/e/s/n zoom box is optional; if
140 specified it means we only trace the flowline if inside this
141 region [Default uses region set by -R]. Requires -L.
142 -S Normalize the resulting CVA grid to percentages of the CVA maxi‐
144 mum. This also normalizes the DI grid (if requested).
145 -Tt|ufixed_val
147 Selects ways to adjust ages; repeatable. Choose from -Tt to
148 truncate crustal ages given via the -A option that exceed the
149 upper age set with -N [no truncation], or -Tufixed_val which
150 means that after a node passes the test implied by -Z, we use
151 this fixed_val instead in the calculations. [Default uses indi‐
152 vidual node values].
153 -V[level] (more ...)
155 Select verbosity level [c].
156 -Wn_try
158 Get n_try bootstrap estimates of the maximum CVA location; the
159 longitude and latitude results are written to stdout [Default is
160 no bootstrapping]. Cannot be used with -M.
161 -Zz_min[/z_max[/z_inc]]
163 Ignore nodes with z-values lower than z_min [0] and optionally
164 larger than z_max [Inf]. Give z_min/z_max/z_inc to make separate
165 CVA grids for each z-slice [Default makes one CVA grid].
166 Multi-slicing cannot be used with -M.
167 -r (more ...)
169 Set pixel node registration [gridline].
170 -^ or just -
172 Print a short message about the syntax of the command, then
173 exits (NOTE: on Windows just use -).
174 -+ or just +
176 Print an extensive usage (help) message, including the explana‐
177 tion of any module-specific option (but not the GMT common
178 options), then exits.
179 -? or no arguments
181 Print a complete usage (help) message, including the explanation
182 of all options, then exits.
183
185 All spherical rotations are applied to geocentric coordinates. This
186 means that incoming data points and grids are considered to represent
187 geodetic coordinates and must first be converted to geocentric coordi‐
188 nates. Rotations are then applied, and the final reconstructed points
189 are converted back to geodetic coordinates. This default behavior can
190 be bypassed if the ellipsoid setting PROJ_ELLIPSOID is changed to
191 Sphere.
192
194 To create a CVA image from the Pacific topography grid Pac_res_topo.nc,
195 using the DC85.d Euler poles, and only output a grid for the specified
196 domain, run
197 gmt grdspotter Pac_res_topo.nc -EDC85.d -GCVA.nc -R190/220/15/25 -I2m -N145 -Tt -V
199 This file can then be plotted with grdimage.
201
203 GMT distributes the EarthByte rotation model Global_Earth‐
204 Byte_230-0Ma_GK07_AREPS.rot. To use an alternate rotation file, create
205 an environmental parameters named GPLATES_ROTATIONS that points to an
206 alternate rotation file.
207
209 gmt, grdimage, project, mapproject, backtracker, gmtpmodeler, grdpmod‐
210 eler, grdrotater, hotspotter, originator
211
213 Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80
214 (29), p. 319.
215 Wessel, P., 2008, Hotspotting: Principles and properties of a plate
217 tectonic Hough transform, Geochem. Geophys. Geosyst. 9(Q08004):
218 doi:10.1029/2008GC002058.
219
221 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
2225.4.5 Feb 24, 2019 GRDSPOTTER(1)