1SPHINTERPOLATE(1) GMT SPHINTERPOLATE(1)
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6 sphinterpolate - Spherical gridding in tension of data on a sphere
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9 sphinterpolate [ table ] -Ggrdfile [ -Iincrement ] [
10 -Qmode[/options] ] [ -Rregion ] [ -V[level] ] [ -Z ] [ -bibinary ] [
11 -dinodata ] [ -eregexp ] [ -hheaders ] [ -iflags ] [ -r ] [ -:[i|o] ]
12 Note: No space is allowed between the option flag and the associated
14 arguments.
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17 sphinterpolate reads one or more ASCII [or binary] files (or standard
18 input) containing lon, lat, z and performs a Delaunay triangulation to
19 set up a spherical interpolation in tension. The final grid is saved to
20 the specified file. Several options may be used to affect the outcome,
21 such as choosing local versus global gradient estimation or optimize
22 the tension selection to satisfy one of four criteria.
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25 -Ggrdfile
26 Name of the output grid to hold the interpolation.
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29 table One or more ASCII (or binary, see -bi[ncols][type]) data table
30 file(s) holding a number of data columns. If no tables are given
31 then we read from standard input.
32 -Ixinc[unit][+e|n][/yinc[unit][+e|n]]
34 x_inc [and optionally y_inc] is the grid spacing. Optionally,
35 append a suffix modifier. Geographical (degrees) coordinates:
36 Append m to indicate arc minutes or s to indicate arc seconds.
37 If one of the units e, f, k, M, n or u is appended instead, the
38 increment is assumed to be given in meter, foot, km, Mile, nau‐
39 tical mile or US survey foot, respectively, and will be con‐
40 verted to the equivalent degrees longitude at the middle lati‐
41 tude of the region (the conversion depends on PROJ_ELLIPSOID).
42 If y_inc is given but set to 0 it will be reset equal to x_inc;
43 otherwise it will be converted to degrees latitude. All coordi‐
44 nates: If +e is appended then the corresponding max x (east) or
45 y (north) may be slightly adjusted to fit exactly the given
46 increment [by default the increment may be adjusted slightly to
47 fit the given domain]. Finally, instead of giving an increment
48 you may specify the number of nodes desired by appending +n to
49 the supplied integer argument; the increment is then recalcu‐
50 lated from the number of nodes and the domain. The resulting
51 increment value depends on whether you have selected a grid‐
52 line-registered or pixel-registered grid; see App-file-formats
53 for details. Note: if -Rgrdfile is used then the grid spacing
54 has already been initialized; use -I to override the values.
55 -Qmode[/options]
57 Specify one of four ways to calculate tension factors to pre‐
58 serve local shape properties or satisfy arc constraints [Default
59 is no tension].
60 -Q0 Piecewise linear interpolation; no tension is applied.
62 -Q1 Smooth interpolation with local gradient estimates.
64 -Q2 Smooth interpolation with global gradient estimates. You may
66 optionally append /N/M/U, where N is the number of iterations
67 used to converge at solutions for gradients when variable ten‐
68 sions are selected (e.g., -T only) [3], M is the number of
69 Gauss-Seidel iterations used when determining the global gradi‐
70 ents [10], and U is the maximum change in a gradient at the last
71 iteration [0.01].
72 -Q3 Smoothing. Optionally append /E/U [/0/0], where E is Expected
74 squared error in a typical (scaled) data value, and U is Upper
75 bound on weighted sum of squares of deviations from data.
76 -Rwest/east/south/north[/zmin/zmax][+r][+uunit]
78 west, east, south, and north specify the region of interest, and
79 you may specify them in decimal degrees or in
80 [±]dd:mm[:ss.xxx][W|E|S|N] format Append +r if lower left and
81 upper right map coordinates are given instead of w/e/s/n. The
82 two shorthands -Rg and -Rd stand for global domain (0/360 and
83 -180/+180 in longitude respectively, with -90/+90 in latitude).
84 Alternatively for grid creation, give Rcodelon/lat/nx/ny, where
85 code is a 2-character combination of L, C, R (for left, center,
86 or right) and T, M, B for top, middle, or bottom. e.g., BL for
87 lower left. This indicates which point on a rectangular region
88 the lon/lat coordinate refers to, and the grid dimensions nx and
89 ny with grid spacings via -I is used to create the corresponding
90 region. Alternatively, specify the name of an existing grid
91 file and the -R settings (and grid spacing, if applicable) are
92 copied from the grid. Appending +uunit expects projected (Carte‐
93 sian) coordinates compatible with chosen -J and we inversely
94 project to determine actual rectangular geographic region. For
95 perspective view (-p), optionally append /zmin/zmax. In case of
96 perspective view (-p), a z-range (zmin, zmax) can be appended to
97 indicate the third dimension. This needs to be done only when
98 using the -Jz option, not when using only the -p option. In the
99 latter case a perspective view of the plane is plotted, with no
100 third dimension.
101 -T Use variable tension (ignored with -Q0 [constant]
103 -V[level] (more ...)
105 Select verbosity level [c].
106 -Z Before interpolation, scale data by the maximum data range [no
108 scaling].
109 -bi[ncols][t] (more ...)
111 Select native binary input. [Default is 3 input columns].
112 -dinodata (more ...)
114 Replace input columns that equal nodata with NaN.
115 -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
117 Only accept data records that match the given pattern.
118 -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
120 Skip or produce header record(s).
121 -:[i|o] (more ...)
123 Swap 1st and 2nd column on input and/or output.
124 -r (more ...)
126 Set pixel node registration [gridline].
127 -^ or just -
129 Print a short message about the syntax of the command, then
130 exits (NOTE: on Windows just use -).
131 -+ or just +
133 Print an extensive usage (help) message, including the explana‐
134 tion of any module-specific option (but not the GMT common
135 options), then exits.
136 -? or no arguments
138 Print a complete usage (help) message, including the explanation
139 of all options, then exits.
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142 The ASCII output formats of numerical data are controlled by parameters
143 in your gmt.conf file. Longitude and latitude are formatted according
144 to FORMAT_GEO_OUT, absolute time is under the control of FOR‐
145 MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point val‐
146 ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for‐
147 mat in effect can lead to loss of precision in ASCII output, which can
148 lead to various problems downstream. If you find the output is not
149 written with enough precision, consider switching to binary output (-bo
150 if available) or specify more decimals using the FORMAT_FLOAT_OUT set‐
151 ting.
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154 To interpolate the points in the file testdata.txt on a global 1x1
155 degree grid with no tension, use
156 sphinterpolate testdata.txt -Rg -I1 -Gsolution.nc
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159 gmt, greenspline, nearneighbor, sphdistance, sphtriangulate, surface,
160 triangulate
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163 Renka, R, J., 1997, Algorithm 772: STRIPACK: Delaunay Triangulation and
164 Voronoi Diagram on the Surface of a Sphere, AMC Trans. Math. Software,
165 23(3), 416-434.
166 Renka, R, J,, 1997, Algorithm 773: SSRFPACK: Interpolation of scattered
168 data on the Surface of a Sphere with a surface under tension, AMC
169 Trans. Math. Software, 23(3), 435-442.
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172 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
1735.4.5 Feb 24, 2019 SPHINTERPOLATE(1)