1GPSGRIDDER(1) GMT GPSGRIDDER(1)
2
6 gpsgridder - Interpolate GPS strain vectors using Green's functions for
7 elastic deformation
8
10 gpsgridder [ table ]
11 -Goutfile [ -Iincrement ] [ -Rregion ] [ -C[n|r|v]value[+ffile] ] [
12 -E[misfitfile] ] [ -F[d|f]fudge] [ -L ] [ -Nnodefile ] [ -Snu ] [
13 -Tmaskgrid ] [ -V[level] ] [ -W[w]] [ -bbinary ] [ -dnodata ] [
14 -eregexp ] [ -fflags ] [ -hheaders ] [ -oflags ] [ -x[[-]n] ] [ -:[i|o]
15 ]
16 Note: No space is allowed between the option flag and the associated
18 arguments.
19
21 gpsgridder grids 2-D vector data such as GPS velocities by using a cou‐
22 pled model based on 2-D elasticity. The degree of coupling can be
23 tuned by adjusting the effective Poisson's ratio. The solution field
24 can be tuned to extremes such as incompressible (1), typical elastic
25 (0.5) or even an unphysical value of -1 that basically removes the
26 elastic coupling of vector interpolation. Smoothing is offered via the
27 optional elimination of small eigenvalues.
28
30 table table with GPS strain rates at discrete locations. We expect
31 the input format to be x y u v [ du dv ] (see -W to specify data
32 uncertainties or weights). If lon lat is given you must supply
33 -fg and we will use a flat Earth approximation in the calcula‐
34 tion of distances.
35 -Goutfile
37 Name of resulting output file. (1) If options -R, -I, and possi‐
38 bly -r are set we produce two equidistant output grids. In this
39 case, outfile must be a name template containing the C format
40 specifier %s, which will be replaced with u and v, respectively.
41 (2) If option -T is selected then -R, -I cannot be given as the
42 maskgrid determines the region and increments. Again, the out‐
43 file must be a name template for the two output grids. (3) If
44 -N is selected then the output is a single ASCII (or binary; see
45 -bo) table written to outfile; if -G is not given then this ta‐
46 ble is written to standard output. The -G option is ignored if
47 -C or -C0 is given.
48
50 -C[n|r|v]value[+ffile]
51 Find an approximate surface fit: Solve the linear system for the
52 spline coefficients by SVD and eliminate the contribution from
53 all eigenvalues whose ratio to the largest eigenvalue is less
54 than value [Default uses Gauss-Jordan elimination to solve the
55 linear system and fit the data exactly]. Optionally, append
56 +ffile to save the eigenvalue ratios to the specified file for
57 further analysis. Finally, if a negative value is given then
58 +ffile is required and execution will stop after saving the ei‐
59 genvalues, i.e., no surface output is produced. Specify
60 -Cvvalue to use the largest eigenvalues needed to explain value
61 % of the data variance. Specify -Crvalue to use the largest ei‐
62 genvalues needed to leave approximately value as the model mis‐
63 fit. If value is not given then -W is required and we compute
64 value as the rms of the given data uncertainties. Alterna‐
65 tively, use -Cnvalue to select the value largest eigenvalues.
66 If a file is given with -Cv then we save the eigenvalues instead
67 of the ratios. Note: 1/4 of the total number of data con‐
68 straints is a good starting point for further experiments.
69 E[misfitfile]
71 Evaluate the spline exactly at the input data locations and report
72 statistics of the misfit (mean, standard deviation, and rms) for u
73 and v separately and combined. Optionally, append a filename and we
74 will write the data table, augmented by two extra columns after each
75 of the u and v columns holding the spline estimates and misfits.
76 -F[d|f]fudge
78 The Green's functions are proportional to terms like 1/r^2 and
79 log(r) and thus blow up for r == 0. To prevent that we offer
80 two fudging schemes: -Fddel_radius lets you add a constant off‐
81 set to all radii and must be specified in the user units.
82 Alternatively, use -Fffactor which will compute del_radius from
83 the product of the shortest inter-point distance and factor
84 [0.01].
85 -Ixinc[unit][+e|n][/yinc[unit][+e|n]]
87 x_inc [and optionally y_inc] is the grid spacing. Optionally,
88 append a suffix modifier. Geographical (degrees) coordinates:
89 Append m to indicate arc minutes or s to indicate arc seconds.
90 If one of the units e, f, k, M, n or u is appended instead, the
91 increment is assumed to be given in meter, foot, km, Mile, nau‐
92 tical mile or US survey foot, respectively, and will be con‐
93 verted to the equivalent degrees longitude at the middle lati‐
94 tude of the region (the conversion depends on PROJ_ELLIPSOID).
95 If y_inc is given but set to 0 it will be reset equal to x_inc;
96 otherwise it will be converted to degrees latitude. All coordi‐
97 nates: If +e is appended then the corresponding max x (east) or
98 y (north) may be slightly adjusted to fit exactly the given
99 increment [by default the increment may be adjusted slightly to
100 fit the given domain]. Finally, instead of giving an increment
101 you may specify the number of nodes desired by appending +n to
102 the supplied integer argument; the increment is then recalcu‐
103 lated from the number of nodes and the domain. The resulting
104 increment value depends on whether you have selected a grid‐
105 line-registered or pixel-registered grid; see App-file-formats
106 for details. Note: if -Rgrdfile is used then the grid spacing
107 has already been initialized; use -I to override the values.
108 -L Leave trend alone. Do not remove a planer (2-D) trend from the
110 data before fitting the spline. [Default removes least squares
111 plane, fits normalized residuals, and restores plane].
112 -Nnodefile
114 ASCII file with coordinates of desired output locations x in the
115 first column(s). The resulting w values are appended to each
116 record and written to the file given in -G [or stdout if not
117 specified]; see -bo for binary output instead. This option elim‐
118 inates the need to specify options -R, -I, and -r.
119 -Rxmin/xmax/ymin/ymax[+r][+uunit] (more ...)
121 Specify the region of interest.
122 -Snu Specify Poisson's ratio to use for this 2-D elastic sheet [0.5].
124 Note: 1.0 is incompressible in a 2-D formulation while -1
125 removes all coupling between the two directions.
126 -Tmaskgrid
128 Only evaluate the solutions at the nodes in the maskgrid that
129 are not set to NaN. This option eliminates the need to specify
130 options -R, -I (and -r).
131 -W[w] One-sigma data uncertainties for u and v are provided in the
133 last two columns. We then compute weights that are inversely
134 proportional to the uncertainties. Append w if weights are
135 given instead of uncertainties. This results in a weighted
136 least squares fit. Note that -W only has an effect if -C is
137 used. [Default uses no weights or uncertainties]. Note: At
138 present the -W option is unstable. We do not yet know if it
139 reflects a coding bug or a theoretical limitation. Users
140 beware, and make sure you compare the results with non-weighted
141 output for basic sanity checking.
142 -V[level] (more ...)
144 Select verbosity level [c].
145 -d[i|o]nodata (more ...)
147 Replace input columns that equal nodata with NaN and do the
148 reverse on output.
149 -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
151 Only accept data records that match the given pattern.
152 -fg Geographic grids (dimensions of longitude, latitude) will be
154 converted to meters via a "Flat Earth" approximation using the
155 current ellipsoid parameters.
156 -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
158 Skip or produce header record(s). Not used with binary data.
159 -icols[+l][+sscale][+ooffset][,...] (more ...)
161 Select input columns and transformations (0 is first column).
162 -r (more ...)
164 Set pixel node registration [gridline].
165 -:[i|o] (more ...)
167 Swap 1st and 2nd column on input and/or output.
168 -^ or just -
170 Print a short message about the syntax of the command, then
171 exits (NOTE: on Windows just use -).
172 -+ or just +
174 Print an extensive usage (help) message, including the explana‐
175 tion of any module-specific option (but not the GMT common
176 options), then exits.
177 -? or no arguments
179 Print a complete usage (help) message, including the explanation
180 of all options, then exits.
181
183 For map distance unit, append unit d for arc degree, m for arc minute,
184 and s for arc second, or e for meter [Default], f for foot, k for km, M
185 for statute mile, n for nautical mile, and u for US survey foot. By
186 default we compute such distances using a spherical approximation with
187 great circles. Prepend - to a distance (or the unit is no distance is
188 given) to perform "Flat Earth" calculations (quicker but less accurate)
189 or prepend + to perform exact geodesic calculations (slower but more
190 accurate).
191
193 To compute the u and v strain rate grids from the GPS data set gps.txt,
194 containing x y u v du dv, on a 2x2 arc minute grid for California, try
195 gmt gpsgridder gps.txt -R-125/-114/31/41 -I2m -fg -W -r -Ggps_strain_%s.nc -V
197
199 Haines, A. J. et al., 2015, Enhanced Surface Imaging of Crustal Defor‐
200 mation, SpringerBriefs in Earth Sciences,
201 doi:10.1007/978-3-319-21578-5_2.
202 Sandwell, D. T. and P. Wessel, 2016, Interpolation of 2-D Vector Data
204 Using Constraints from Elasticity, Geophys. Res. Lett., 43,
205 10,703-10,709, http://dx.doi.org/10.1002/2016GL070340
206
208 gmt, greenspline nearneighbor, surface
209
211 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
2125.4.5 Feb 24, 2019 GPSGRIDDER(1)