pygmt.triangulate.regular_grid

static triangulate.regular_grid(data=None, x=None, y=None, z=None, outgrid=None, **kwargs)

Delaunay triangle based gridding of Cartesian data.

Reads in x,y[,z] data and performs Delaunay triangulation, i.e., it finds how the points should be connected to give the most equilateral triangulation possible. If a map projection (give region and projection) is chosen then it is applied before the triangulation is calculated. By setting outgrid and spacing, a grid will be calculated based on the surface defined by the planar triangles. The actual algorithm used in the triangulations is either that of Watson [1982] or Shewchuk [1996] [Default is Shewchuk if installed; type gmt get GMT_TRIANGULATE on the command line to see which method is selected]. This choice is made during the GMT installation. Furthermore, if the Shewchuk algorithm is installed then you can also perform the calculation of Voronoi polygons and optionally grid your data via the natural nearest neighbor algorithm.

Must provide either data or x, y, and z.

Must provide region and spacing.

Full option list at https://docs.generic-mapping-tools.org/6.5/triangulate.html

Aliases:

• I = spacing

• J = projection

• R = region

• V = verbose

• b = binary

• d = nodata

• e = find

• f = coltypes

• h = header

• i = incols

• r = registration

• s = skiprows

• w = wrap

Parameters:

• x/y/z (np.ndarray) – Arrays of x and y coordinates and values z of the data points.

• data (str, numpy.ndarray, pandas.DataFrame, xarray.Dataset, or geopandas.GeoDataFrame) – Pass in (x, y[, z]) or (longitude, latitude[, elevation]) values by providing a file name to an ASCII data table, a 2-D numpy.ndarray, a pandas.DataFrame, an xarray.Dataset made up of 1-D xarray.DataArray data variables, or a geopandas.GeoDataFrame containing the tabular data.

• projection (str) – projcode[projparams/]width|scale. Select map projection.

• region (str or list) – xmin/xmax/ymin/ymax[+r][+uunit]. Specify the region of interest.

• spacing (float, str, or list) –

  x_inc[+e|n][/y_inc[+e|n]]. x_inc [and optionally y_inc] is the grid spacing.

  • Geographical (degrees) coordinates: Optionally, append an increment unit. Choose among m to indicate arc-minutes or s to indicate arc-seconds. If one of the units e, f, k, M, n or u is appended instead, the increment is assumed to be given in meter, foot, km, mile, nautical mile or US survey foot, respectively, and will be converted to the equivalent degrees longitude at the middle latitude of the region (the conversion depends on PROJ_ELLIPSOID). If y_inc is given but set to 0 it will be reset equal to x_inc; otherwise it will be converted to degrees latitude.

  • All coordinates: If +e is appended then the corresponding max x (east) or y (north) may be slightly adjusted to fit exactly the given increment [by default the increment may be adjusted slightly to fit the given domain]. Finally, instead of giving an increment you may specify the number of nodes desired by appending +n to the supplied integer argument; the increment is then recalculated from the number of nodes, the registration, and the domain. The resulting increment value depends on whether you have selected a gridline-registered or pixel-registered grid; see GMT File Formats for details.

  Note: If region=grdfile is used then the grid spacing and the registration have already been initialized; use spacing and registration to override these values.

• outgrid (str | None, default: None) –

  Name of the output netCDF grid file. If not specified, will return an xarray.DataArray object. For writing a specific grid file format or applying basic data operations to the output grid, see https://docs.generic-mapping-tools.org/6.5/gmt.html#grd-inout-full for the available modifiers.

  The interpolation is performed in the original coordinates, so if your triangles are close to the poles you are better off projecting all data to a local coordinate system before using triangulate (this is true of all gridding routines) or instead select sphtriangulate.

• verbose (bool or str) –

  Select verbosity level [Default is w], which modulates the messages written to stderr. Choose among 7 levels of verbosity:

  • q - Quiet, not even fatal error messages are produced

  • e - Error messages only

  • w - Warnings [Default]

  • t - Timings (report runtimes for time-intensive algorithms)

  • i - Informational messages (same as verbose=True)

  • c - Compatibility warnings

  • d - Debugging messages

• binary (bool or str) –

  i|o[ncols][type][w][+l|b]. Select native binary input (using binary="i") or output (using binary="o"), where ncols is the number of data columns of type, which must be one of:

  • c - int8_t (1-byte signed char)

  • u - uint8_t (1-byte unsigned char)

  • h - int16_t (2-byte signed int)

  • H - uint16_t (2-byte unsigned int)

  • i - int32_t (4-byte signed int)

  • I - uint32_t (4-byte unsigned int)

  • l - int64_t (8-byte signed int)

  • L - uint64_t (8-byte unsigned int)

  • f - 4-byte single-precision float

  • d - 8-byte double-precision float

  • x - use to skip ncols anywhere in the record

  For records with mixed types, append additional comma-separated combinations of ncols type (no space). The following modifiers are supported:

  • w after any item to force byte-swapping.

  • +l|b to indicate that the entire data file should be read as little- or big-endian, respectively.

  Full documentation is at https://docs.generic-mapping-tools.org/6.5/gmt.html#bi-full.

• nodata (str) – i|onodata. Substitute specific values with NaN (for tabular data). For example, nodata="-9999" will replace all values equal to -9999 with NaN during input and all NaN values with -9999 during output. Prepend i to the nodata value for input columns only. Prepend o to the nodata value for output columns only.

• find (str) – [~]“pattern” | [~]/regexp/[i]. Only pass records that match the given pattern or regular expressions [Default processes all records]. Prepend ~ to the pattern or regexp to instead only pass data expressions that do not match the pattern. Append i for case insensitive matching. This does not apply to headers or segment headers.

• coltypes (str) – [i|o]colinfo. Specify data types of input and/or output columns (time or geographical data). Full documentation is at https://docs.generic-mapping-tools.org/6.5/gmt.html#f-full.

• header (str) –

  [i|o][n][+c][+d][+msegheader][+rremark][+ttitle]. Specify that input and/or output file(s) have n header records [Default is 0]. Prepend i if only the primary input should have header records. Prepend o to control the writing of header records, with the following modifiers supported:

  • +d to remove existing header records.

  • +c to add a header comment with column names to the output [Default is no column names].

  • +m to add a segment header segheader to the output after the header block [Default is no segment header].

  • +r to add a remark comment to the output [Default is no comment]. The remark string may contain \n to indicate line-breaks.

  • +t to add a title comment to the output [Default is no title]. The title string may contain \n to indicate line-breaks.

  Blank lines and lines starting with # are always skipped.

• incols (str or 1-D array) –

  Specify data columns for primary input in arbitrary order. Columns can be repeated and columns not listed will be skipped [Default reads all columns in order, starting with the first (i.e., column 0)].

  • For 1-D array: specify individual columns in input order (e.g., incols=[1,0] for the 2nd column followed by the 1st column).

  • For str: specify individual columns or column ranges in the format start[:inc]:stop, where inc defaults to 1 if not specified, with columns and/or column ranges separated by commas (e.g., incols="0:2,4+l" to input the first three columns followed by the log-transformed 5th column). To read from a given column until the end of the record, leave off stop when specifying the column range. To read trailing text, add the column t. Append the word number to t to ingest only a single word from the trailing text. Instead of specifying columns, use incols="n" to simply read numerical input and skip trailing text. Optionally, append one of the following modifiers to any column or column range to transform the input columns:

    • +l to take the log10 of the input values.

    • +d to divide the input values by the factor divisor [Default is 1].

    • +s to multiple the input values by the factor scale [Default is 1].

    • +o to add the given offset to the input values [Default is 0].

• registration (str) – g|p. Force gridline (g) or pixel (p) node registration [Default is g(ridline)].

• skiprows (bool or str) –

  [cols][+a][+r]. Suppress output for records whose z-value equals NaN [Default outputs all records]. Optionally, supply a comma-separated list of all columns or column ranges to consider for this NaN test [Default only considers the third data column (i.e., cols = 2)]. Column ranges must be given in the format start[:inc]:stop, where inc defaults to 1 if not specified. The following modifiers are supported:

  • +r to reverse the suppression, i.e., only output the records whose z-value equals NaN.

  • +a to suppress the output of the record if just one or more of the columns equal NaN [Default skips record only if values in all specified cols equal NaN].

• wrap (str) –

  y|a|w|d|h|m|s|cperiod[/phase][+ccol]. Convert the input x-coordinate to a cyclical coordinate, or a different column if selected via +ccol. The following cyclical coordinate transformations are supported:

  • y - yearly cycle (normalized)

  • a - annual cycle (monthly)

  • w - weekly cycle (day)

  • d - daily cycle (hour)

  • h - hourly cycle (minute)

  • m - minute cycle (second)

  • s - second cycle (second)

  • c - custom cycle (normalized)

  Full documentation is at https://docs.generic-mapping-tools.org/6.5/gmt.html#w-full.

Returns:

ret (xarray.DataArray or None) – Return type depends on whether the outgrid parameter is set:

• xarray.DataArray if outgrid is None (default)

• None if outgrid is a str (grid output is stored in outgrid)

Note

For geographic data with global or very large extent you should consider sphtriangulate instead since triangulate is a Cartesian or small-geographic area operator and is unaware of periodic or polar boundary conditions.