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 ] [ -M ] [ -Nupper_age ] [
12 -PPAgrid ] [ -QIDinfo ] [ -S ] [ -T ] [ -Ufixed_val ] [ -V ] [
13 -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 poles and opening angles. This file
29 must contain one record for each stage; each record must be of
30 the following format:
31 lon lat tstart tstop ccw-angle
33 where tstart and tstop are in Ma and the rest is in degrees.
35 The oldest stage must be listed first. tstart (tstop) is the
36 age of the old (young) end of the stage. Blank lines and
37 records whose first column contains # will be ignored. However,
38 see -C for total recostruction poles.
39 -G Specify name for output CVA grid file.
41 -I x_inc [and optionally y_inc] is the grid spacing. Optionally,
43 append a suffix modifier. Geographical (degrees) coordinates:
44 Append m to indicate arc minutes or c to indicate arc seconds.
45 If one of the units e, k, i, or n is appended instead, the
46 increment is assumed to be given in meter, km, miles, or nauti‐
47 cal miles, respectively, and will be converted to the equivalent
48 degrees longitude at the middle latitude of the region (the con‐
49 version depends on ELLIPSOID). If /y_inc is given but set to 0
50 it will be reset equal to x_inc; otherwise it will be converted
51 to degrees latitude. All coordinates: If = is appended then the
52 corresponding max x (east) or y (north) may be slightly adjusted
53 to fit exactly the given increment [by default the increment may
54 be adjusted slightly to fit the given domain]. Finally, instead
55 of giving an increment you may specify the number of nodes
56 desired by appending + to the supplied integer argument; the
57 increment is then recalculated from the number of nodes and the
58 domain. The resulting increment value depends on whether you
59 have selected a gridline-registered or pixel-registered grid;
60 see Appendix B for details.
61 -R west, east, south, and north specify the Region of interest, and
63 you may specify them in decimal degrees or in
64 [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left and
65 upper right map coordinates are given instead of w/e/s/n. The
66 two shorthands -Rg and -Rd stand for global domain (0/360 and
67 -180/+180 in longitude respectively, with -90/+90 in latitude).
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70 -A Supply a crustal age grid that is co-registered with the input
71 data grid. These ages become the upper ages to use when con‐
72 structing flowlines [Default extend flowlines back to oldest age
73 found in the rotation file; but see -N].
74 -B Get n_try bootstrap estimates of the maximum CVA location; the
76 longitude and latitude results are written to stdout [Default is
77 no bootstrapping]. Cannot be used with -M.
78 -C Expect Total Reconstruction Poles rather than Backward Stage
80 Poles [Default]. File format is similar to the stage pole for‐
81 mat except the youngest rotation must be listed first and that
82 the tstart column is optional (assumed to be 0 Ma).
83 -D Use flowlines to determine the maximum CVA encountered along
85 each flowline and create a Data Importance (DI) grid with these
86 values at the originating nodes.
87 -F Force pixel registration [Default is grid registration].
89 -L Supply a co-registered grid with seamount chain IDs for each
91 node. This option requires that you also use -Q.
92 -M Do not attempt to keep all flowlines in memory when using -D
94 and/or -P. Should you run out of memory you can use this option
95 to compute flowlines on-the-fly. It will be slower as we no
96 longer can reuse the flowlines calculated for the CVA step.
97 Cannot be used with -B or the multi-slice mode in -Z.
98 -N Set the upper age to assign to nodes whose crustal age is
100 unknown (i.e., NaN) [no upper age]. Also see -A.
101 -P Use flowlines to determine the flowline age at the CVA maximum
103 for each node and create a Predicted Age (PA) grid with these
104 values at the originating nodes.
105 -Q Either give (1) a single ID to use or (2) the name of a file
107 with a list of IDs to use [Default uses all IDs]. Each line
108 would be TAG ID [w e s n]. The w/e/s/n zoom box is optional; if
109 specified it means we only trace the flowline if inside this
110 region [Default uses region set by -R]. Requires -L.
111 -S Normalize the resulting CVA grid to percentages of the CVA maxi‐
113 mum. This also normalizes the DI grid (if requested).
114 -T Truncate crustal ages given via the -A option that exceed the
116 upper age set with -N [no truncation].
117 -U After a node passes the test implied by -Z, use this fixed_val
119 instead in the calculations. [Default uses individual node val‐
120 ues].
121 -V Selects verbose mode, which will send progress reports to stderr
123 [Default runs "silently"].
124 -Z Ignore nodes with z-values lower than z_min [0] and optionally
126 larger than z_max [Inf]. Give z_min/z_max/z_inc to make sepa‐
127 rate CVA grids for each z-slice [Default makes one CVA grid].
128 Multi-slicing cannot be used with -M.
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131 To create a CVA image from the Pacific topography grid
132 Pac_res_topo.grd, using the DC85.d Euler poles, and only output a grid
133 for the specified domain, run
134 grdspotter Pac_res_topo.grd -EDC85.d -GCVA.grd -R190/220/15/25 -I2m
136 -N145 -T -V
137 This file can then be plotted with grdimage.
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141 GMT(1), grdimage(1), project(1), mapproject(1), backtracker(1),
142 hotspotter(1), originator(1)
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145 Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80
146 (29), p. 319.
147GMT 4.3.1 15 May 2008 GRDSPOTTER(1)