**-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
**--ui**- Force launching GUI dialog

**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*

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.

g.region -p rast=elev_state_500m

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

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

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

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
*

- 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

Available at: v.surf.tps source code (history)

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