DK11 for Delphi | GisInterpolation.TGIS_InterpolationSplines | Classes | Constructors | Methods | Properties
Implementation of the Completely Regularized Splines (CRS) interpolation method.
// Delphi type TGIS_InterpolationSplines = class( TGIS_VectorToGridAbstract ) end;
// C++ Builder class PASCALIMPLEMENTATION TGIS_InterpolationSplines : public TGIS_VectorToGridAbstract { };
→ TObject → TGIS_BaseObjectDisposable → TGIS_VectorToGridAbstract
Name | Visibility | Description | |
---|---|---|---|
Generate | public | Populates a pixel (grid) layer with values resulting from computations based on the set of sample points from the vector layer. _{ (Overrides TGIS_VectorToGridAbstract.Generate) } | |
raiseBusyEvent | protected | Prepares and raises the BusyEvent. _{ (Inherited from TGIS_VectorToGridAbstract) } | |
Name | Visibility | Description | |
---|---|---|---|
Coordinate | public | Defines which coordinate is taken as interpolation value if the interpolation is not based on an attribute field; default is Z. _{ (Inherited from TGIS_VectorToGridAbstract)} | |
DefaultValue | public | If UseDefaultValue is true, then this value will be set for each grid cell for which the interpolated value cannot be computed. _{ (Inherited from TGIS_VectorToGridAbstract)} | |
MaxPoints | public | The maximum number of input data points used to interpolate at each grid cell; default is 4. _{} | |
MinPoints | public | The minimum number of input data points used to interpolate at each grid cell; default is 4. _{} | |
Radius | public | Applies only to the windowed method (Windowed = True). _{} | |
Tension | public | The tension (smoothing) factor. _{} | |
UseDefaultValue | public | If true, then each grid cell for which the interpolated value cannot be computed will be set to DefaultValue. _{ (Inherited from TGIS_VectorToGridAbstract)} | |
Windowed | public | If True then the windowed version of the algorithm is used; true by default. _{} | |
The principal of the Completely Regularized Splines interpolation method is to minimize the overall surface curvature. It produces the smoothest results among the vector-to-grid interpolation techniques.
There are two different scenarios for generating a splines interpolated grid:
Coordinate
property to the desired optionGenerate
methodGenerate
methodCoordinate
property is neglected
The Tension
parameter is a smoothening factor - the smaller the tension the less rapid changes in the interpolated values. For best results it must be experimentally adjusted for each input dataset. The most common values of Tension
(that are good to start with) are in the range of 0,00001 to 0,1.
Use a windowed version of the algorithm (Windowed=True
) for large datasets (thousands of points and more). For up to a few hundred points, the non-windowed (full sample) algorithm is efficient enough and gives best possible results. The Radius
property is the size of the window in map units. The MinPoints/MaxPoints properties define the minimum/maximum number of sample points necessary/taken to interpolate a grid value.
var src : TGIS_LayerVector ; dst : TGIS_LayerPixel ; vtg : TGIS_InterpolationSplines ; ext : TGIS_Extent ; begin // get the source layer (GIS is TGIS_ViewerWnd) src := TGIS_LayerVector( GIS.Get( 'points' ) ) ; ext := src.Extent ; // create the destination layer (grid, 200x200 pixels) dst := TGIS_LayerPixel.Create ; dst.Build( True, lsrc.CS, ext, 200, 200 ) ; dst.Name := 'Heatmap' ; dst.Params.Pixel.GridShadow := False ; // create an instance of the splines interpolation engine vtg := TGIS_InterpolationSplines .Create ; try // attach event to track the progress vtg.BusyEvent := doBusyEvent ; // set the tension parameter vtg.Tension := 0.0001 ; // initiate the grid generation process for the // POPULATION attribute field vtg.Import( lsrc, ext, 'POPULATION', ldst, ext ) ; finally vtg.Free ; end ; // add the grid to the viewer GIS.Add( dst ) ; // update the viewer GIS.FullExtent ; end ;