1GRDSPOTTER(1) Generic Mapping Tools GRDSPOTTER(1)
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6 grdspotter - Create CVA image directly from gravity or bathymetry grids
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9 grdspotter [grdfile] -Erotations_file -GCVAgrid
10 -Ixinc[unit][=|+][/yinc[unit][=|+]] -Rwest/east/south/north[r] [ -Aage‐
11 grid ] [ -Bn_try ] [ -C ] [ -DDIgrid ] [ -F ] [ -LIT(IDgrid) ] [ -M ] [
12 -Nupper_age ] [ -PPAgrid ] [ -QIDinfo ] [ -S ] [ -T ] [ -Ufixed_val ] [
13 -V ] [ -Zz_min[/z_max[/z_inc]] ]
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16 grdspotter reads a grid file with residual bathymetry or gravity and
17 calculates flowlines from each node that exceeds a minimum value using
18 the specified rotations file. These flowlines are then convolved with
19 the volume of the prism represented by each grid node and added up to
20 give a Cumulative Volcano Amplitude grid (CVA).
21 No space between the option flag and the associated arguments.
22 Use upper case for the option flags and lower case for modifiers.
23 grdfile
25 Data grid to be processed, typically residual bathymetry or
26 free-air anomalies.
27 -E Give file with rotation parameters. This file must contain one
29 record for each rotation; each record must be of the following
30 format:
31 lon lat tstart [tstop] angle [ khat a b c d e f g df ]
33 where tstart and tstop are in Myr and lon lat angle are in
35 degrees. tstart and tstop are the ages of the old and young
36 ends of a stage. If -C is set then a total reconstruction rota‐
37 tion is expected and tstop is implicitly set to 0 and should not
38 be specified in the file. If a covariance matrix C for the
39 rotation is available it must be specified in a format using the
40 nine optional terms listed in brackets. Here, C = (g/khat)*[ a
41 b d; b c e; d e f ] which shows C made up of three row vectors.
42 If the degrees of freedom (df) in fitting the rotation is 0 or
43 not given it is set to 10000. Blank lines and records whose
44 first column contains # will be ignored.
45 -G Specify name for output CVA grid file.
47 -I x_inc [and optionally y_inc] is the grid spacing. Optionally,
49 append a suffix modifier. Geographical (degrees) coordinates:
50 Append m to indicate arc minutes or c to indicate arc seconds.
51 If one of the units e, k, i, or n is appended instead, the
52 increment is assumed to be given in meter, km, miles, or nauti‐
53 cal miles, respectively, and will be converted to the equivalent
54 degrees longitude at the middle latitude of the region (the con‐
55 version depends on ELLIPSOID). If /y_inc is given but set to 0
56 it will be reset equal to x_inc; otherwise it will be converted
57 to degrees latitude. All coordinates: If = is appended then the
58 corresponding max x (east) or y (north) may be slightly adjusted
59 to fit exactly the given increment [by default the increment may
60 be adjusted slightly to fit the given domain]. Finally, instead
61 of giving an increment you may specify the number of nodes
62 desired by appending + to the supplied integer argument; the
63 increment is then recalculated from the number of nodes and the
64 domain. The resulting increment value depends on whether you
65 have selected a gridline-registered or pixel-registered grid;
66 see Appendix B for details. Note: if -Rgrdfile is used then
67 grid spacing has already been initialized; use -I to override
68 the values.
69 -R west, east, south, and north specify the Region of interest, and
71 you may specify them in decimal degrees or in
72 [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left and
73 upper right map coordinates are given instead of w/e/s/n. The
74 two shorthands -Rg and -Rd stand for global domain (0/360 and
75 -180/+180 in longitude respectively, with -90/+90 in latitude).
76 Alternatively, specify the name of an existing grid file and the
77 -R settings (and grid spacing, if applicable) are copied from
78 the grid.
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81 -A Supply a crustal age grid that is co-registered with the input
82 data grid. These ages become the upper ages to use when con‐
83 structing flowlines [Default extend flowlines back to oldest age
84 found in the rotation file; but see -N].
85 -B Get n_try bootstrap estimates of the maximum CVA location; the
87 longitude and latitude results are written to stdout [Default is
88 no bootstrapping]. Cannot be used with -M.
89 -C Expect Total Reconstruction Rotations rather than Forward Stage
91 Rotations [Default]. File format is similar to the stage pole
92 format except that the tstart column is not present (assumed to
93 be 0 Ma).
94 -D Use flowlines to determine the maximum CVA encountered along
96 each flowline and create a Data Importance (DI) grid with these
97 values at the originating nodes.
98 -F Force pixel registration [Default is grid registration].
100 -L Supply a co-registered grid with seamount chain IDs for each
102 node. This option requires that you also use -Q.
103 -M Do not attempt to keep all flowlines in memory when using -D
105 and/or -P. Should you run out of memory you can use this option
106 to compute flowlines on-the-fly. It will be slower as we no
107 longer can reuse the flowlines calculated for the CVA step.
108 Cannot be used with -B or the multi-slice mode in -Z.
109 -N Set the upper age to assign to nodes whose crustal age is
111 unknown (i.e., NaN) [no upper age]. Also see -A.
112 -P Use flowlines to determine the flowline age at the CVA maximum
114 for each node and create a Predicted Age (PA) grid with these
115 values at the originating nodes.
116 -Q Either give (1) a single ID to use or (2) the name of a file
118 with a list of IDs to use [Default uses all IDs]. Each line
119 would be TAG ID [w e s n]. The w/e/s/n zoom box is optional; if
120 specified it means we only trace the flowline if inside this
121 region [Default uses region set by -R]. Requires -L.
122 -S Normalize the resulting CVA grid to percentages of the CVA maxi‐
124 mum. This also normalizes the DI grid (if requested).
125 -T Truncate crustal ages given via the -A option that exceed the
127 upper age set with -N [no truncation].
128 -U After a node passes the test implied by -Z, use this fixed_val
130 instead in the calculations. [Default uses individual node val‐
131 ues].
132 -V Selects verbose mode, which will send progress reports to stderr
134 [Default runs "silently"].
135 -Z Ignore nodes with z-values lower than z_min [0] and optionally
137 larger than z_max [Inf]. Give z_min/z_max/z_inc to make sepa‐
138 rate CVA grids for each z-slice [Default makes one CVA grid].
139 Multi-slicing cannot be used with -M.
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142 To create a CVA image from the Pacific topography grid
143 Pac_res_topo.grd, using the DC85.d Euler poles, and only output a grid
144 for the specified domain, run
145 grdspotter Pac_res_topo.grd -EDC85.d -GCVA.grd -R190/220/15/25 -I2m
147 -N145 -T -V
148 This file can then be plotted with grdimage.
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152 Data coordinates are assumed to be geodetic and will automatically be
153 converted to geocentric before spherical rotations are performed. We
154 convert back to geodetic coordinates for output. Note: If your data
155 already are geocentric, you can avoid the conversion by using --ELLIP‐
156 SOID=sphere.
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159 GMT(1), grdimage(1), grdrotater(1), project(1), mapproject(1), back‐
160 tracker(1), hotspotter(1), originator(1)
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163 Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80
164 (29), p. 319.
165GMT 4.5.6 10 Mar 2011 GRDSPOTTER(1)