v.surf.tps

Performs thin plate spline interpolation with regularization and covariables.

v.surf.tps [-c] input=name [layer=string] [column=name] [smooth=float] [overlap=float] [min=float] [covars=name [,name,...]] [thin=float] output=name [mask=name] [memory=integer] [--overwrite] [--verbose] [--quiet] [--qq] [--ui]

Example:

v.surf.tps input=name output=name

grass.script.run_command("v.surf.tps", input, layer="1", column=None, smooth=0, overlap=0.1, min=20, covars=None, thin=1.5, output, mask=None, memory=300, flags=None, overwrite=False, verbose=False, quiet=False, superquiet=False)

Example:

gs.run_command("v.surf.tps", input="name", output="name")

Parameters

Command linePython (grass.script)

input=name [required]
    Name of input vector point map
    Or data source for direct OGR access
layer=string
    Layer number or name
    Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
    Default: 1
column=name
    Name of the attribute column with values to be used for interpolation
    If not given, z-coordinates are used.
smooth=float
    Smoothing factor
    Default: 0
overlap=float
    Overlap factor <= 1
    A larger value increase the tile overlap
    Default: 0.1
min=float
    Minimum number of points to use for TPS interpolation
    Default: 20
covars=name [,name,...]
    Name of input raster map(s) to use as covariables
    Name of input raster map(s)
thin=float
    Point cloud thinning factor in number of cells of the current region
    Minimum distance between neighboring points for local TPS interpolation
    Default: 1.5
output=name [required]
    Name for output raster map
mask=name
    Raster map to use for masking
    Only cells that are not NULL and not zero are interpolated
memory=integer
    Memory in MB
    Default: 300
-c
    Input points are dense clusters separated by empty areas
--overwrite
    Allow output files to overwrite existing files
--help
    Print usage summary
--verbose
    Verbose module output
--quiet
    Quiet module output
--qq
    Very quiet module output
--ui
    Force launching GUI dialog

input : str, required
    Name of input vector point map
    Or data source for direct OGR access
    Used as: input, vector, name
layer : str, optional
    Layer number or name
    Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
    Used as: input, layer
    Default: 1
column : str, optional
    Name of the attribute column with values to be used for interpolation
    If not given, z-coordinates are used.
    Used as: input, dbcolumn, name
smooth : float, optional
    Smoothing factor
    Default: 0
overlap : float, optional
    Overlap factor <= 1
    A larger value increase the tile overlap
    Default: 0.1
min : float, optional
    Minimum number of points to use for TPS interpolation
    Default: 20
covars : str | list[str], optional
    Name of input raster map(s) to use as covariables
    Name of input raster map(s)
    Used as: input, raster, name
thin : float, optional
    Point cloud thinning factor in number of cells of the current region
    Minimum distance between neighboring points for local TPS interpolation
    Default: 1.5
output : str, required
    Name for output raster map
    Used as: output, raster, name
mask : str, optional
    Raster map to use for masking
    Only cells that are not NULL and not zero are interpolated
    Used as: input, raster, name
memory : int, optional
    Memory in MB
    Default: 300
flags : str, optional
    Allowed values: c
    c
        Input points are dense clusters separated by empty areas
overwrite: bool, optional
    Allow output files to overwrite existing files
    Default: False
verbose: bool, optional
    Verbose module output
    Default: False
quiet: bool, optional
    Quiet module output
    Default: False
superquiet: bool, optional
    Very quiet module output
    Default: False

DESCRIPTION

v.surf.tps performs multivariate thin plate spline interpolation with regularization. The input is a 2D or 3D vector points map. Values to interpolate can be the z values of 3D points or the values in a user-specified attribute column in a 2D or 3D vector map. Output is a raster map. Optionally, several raster maps can be specified to be used as covariables which will improve results in areas with few points. The module can be regarded as a combination of a multiple regression and spline interpolation.

The min options specifies the minimum number of points to be used for interpolation. If the number of input points is smaller than or equal to the minimum number of points, global TPS interpolation is used. If the number of input points is larger than the minimum number of points, tiled local TPS interpolation is used. Tile sizes are variable and dependent on the extents of the min nearest neighbors when a new tile is generated.

The smooth option can be used to reduce the influence of the splines and increase the influence of the covariables. Without covariables, the resulting surface will be smoother. With covariables and a large smooting value, the resulting surface will be mainly determined by the multiple regression component.

The overlap option controls how much tiles are overlapping when the min option is smaller than the numer of input points. Tiling artefacts occur with low values for the min option and the overlap option. Increasing both options will reduce tiling artefacts but processing will take more time. Values for the overlap option must be between 0 and 1.

The module works best with evenly spaced sparse points. In case of highly unevenly spaced points, e.g. remote sensing data with gaps due to cloud cover, the thin option should be used in order to avoid tiling artefacts, otherwise a high number of minimum points and a large overlap value are required, slowing down the module.

The memory option controls only how much memory should be used for the covariables and the intermediate output. The input points are always completely loaded to memory.

EXAMPLES

The computational region setting for the following examples:

g.region -p rast=elev_state_500m

Basic interpolation

Interpolation of 30 year precipitation normals in the North Carlolina sample dataset:

v.surf.tps input=precip_30ynormals_3d output=precip_30ynormals_3d \
           column=annual min=140

Interpolation with a covariable

v.surf.tps input=precip_30ynormals_3d output=precip_30ynormals_3d \
           column=annual min=140 covars=elev_state_500m

Interpolation with a covariable and smoothing

v.surf.tps input=precip_30ynormals_3d output=precip_30ynormals_3d \
           column=annual min=140 covars=elev_state_500m smooth=0.1

Tiled interpolation with a covariable and smoothing

v.surf.tps input=precip_30ynormals_3d output=precip_30ynormals_3d \
           column=annual min=20 covars=elev_state_500m smooth=0.1 \
           overlap=0.1

Precipitation computed based on annual normals and elevation as a covariable

REFERENCES

Hutchinson MF, 1995, Interpolating mean rainfall using thin plate smoothing splines. International Journal of Geographical Information Systems, 9(4), pp. 385-403
Wahba G, 1990, Spline models for observational data. In CBMS-NSF Regional Conference Series in Applied Mathematics. Philadelpia: Society for Industrial and Applied Mathematics

AUTHOR

Markus Metz

SOURCE CODE

Available at: v.surf.tps source code (history)
Latest change: Friday Feb 21 10:10:05 2025 in commit 7d78fe3