pygmt.grdsample

pygmt.grdsample(grid, outgrid=None, **kwargs)

Change the registration, spacing, or nodes in a grid file.

This reads a grid file and interpolates it to create a new grid file. It can change the registration with translate or registration, change the grid-spacing or number of nodes with spacing, and set a new sub-region using region. A bicubic [Default], bilinear, B-spline or nearest-neighbor interpolation is set with interpolation.

When region is omitted, the output grid will cover the same region as the input grid. When spacing is omitted, the grid spacing of the output grid will be the same as the input grid. Either registration or translate can be used to change the grid registration. When omitted, the output grid will have the same registration as the input grid.

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

Aliases:

• I = spacing

• R = region

• T = translate

• V = verbose

• f = coltypes

• n = interpolation

• r = registration

• x = cores

Parameters:

• grid (str or xarray.DataArray) –

  Name of the input grid file or the grid loaded as a xarray.DataArray object.

  For reading a specific grid file format or applying basic data operations, see https://docs.generic-mapping-tools.org/6.5/gmt.html#grd-inout-full for the available modifiers.

• 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.

• 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.

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

• translate (bool) – Translate between grid and pixel registration; if the input is grid-registered, the output will be pixel-registered and vice-versa.

• registration (str or bool) – [g|p]. Set registration to gridline or pixel.

• 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

• 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.

• interpolation (str) –

  [b|c|l|n][+a][+bBC][+c][+tthreshold]. Select interpolation mode for grids. You can select the type of spline used:

  • b for B-spline

  • c for bicubic [Default]

  • l for bilinear

  • n for nearest-neighbor

• cores (bool or int) – [[-]n]. Limit the number of cores to be used in any OpenMP-enabled multi-threaded algorithms. By default we try to use all available cores. Set a number n to only use n cores (if too large it will be truncated to the maximum cores available). Finally, give a negative number -n to select (all - n) cores (or at least 1 if n equals or exceeds all).

Returns:

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

• xarray.DataArray if outgrid is not set

• None if outgrid is set (grid output will be stored in file set by outgrid)

Example

>>> import pygmt
>>> # Load a grid of @earth_relief_30m data, with a longitude range of
>>> # 10° E to 30° E, and a latitude range of 15° N to 25° N
>>> grid = pygmt.datasets.load_earth_relief(
...     resolution="30m", region=[10, 30, 15, 25]
... )
>>> # Create a new grid from an input grid, change the registration,
>>> # and set both x- and y-spacing to 0.5 arc-degrees
>>> new_grid = pygmt.grdsample(grid=grid, translate=True, spacing=[0.5, 0.5])