Table of Contents
TGIS_InterpolationIDW class
DK11 for ActiveX | TatukGIS_XDK11.TGIS_InterpolationIDW | Classes | Methods | Properties
Implementation of the Inverse Distance Weighting (IDW) interpolation method.
Syntax
// C# public class TGIS_InterpolationIDW : ITGIS_InterpolationIDW, ITGIS_VectorToGridAbstractEvents { }
' VisualBasic Public Class TGIS_InterpolationIDW Implements ITGIS_InterpolationIDW Implements ITGIS_VectorToGridAbstractEvents End Class
// Oxygene type TGIS_InterpolationIDW = public class end;
Implements
Methods
| Name | Visibility | Description | |
|---|---|---|---|
| AttachDelphiObj | public | Only for internal use of TatukGIS. (Inherited from ITBaseObject) |
|
| BusyEvent | public | (Inherited from ITGIS_VectorToGridAbstractEvents) |
|
| DelphiObj | public | Only for internal use of TatukGIS. (Inherited from ITBaseObject) |
|
| Generate | public | Populates a pixel (grid) layer with values resulting from computations based on the set of sample points from the vector layer. (Inherited from ITGIS_VectorToGridAbstract) |
|
Properties
| 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 ITGIS_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 ITGIS_VectorToGridAbstract) |
|
| Exponent | public | Exponent in the formula for weight calculation; default value is 2. | |
| Radius | public | Applies only to the windowed method (Windowed = True). | |
| UseDefaultValue | public | If true, then each grid cell for which the interpolated value cannot be computed will be set to DefaultValue. (Inherited from ITGIS_VectorToGridAbstract) |
|
| Windowed | public | If True then the windowed version of the algorithm is used; true by default. | |
Remarks
Method
The Inverse Distance Squared (IDW) interpolation method assumes that the influence of the data points on the interpolated point diminishes with distance, i.e., nearby points have greater weight than points that are further away.
Usage
There are two different scenarios for generating an IDW interpolated grid:
- based on a Z, M, or Z+M coordinate value:
- set the
Coordinateproperty to the desired option - pass an empty string as the field name to the
Generatemethod
- based on an attribute field value:
- pass the field name to the
Generatemethod - with above the
Coordinateproperty is neglected
The Exponent property plays the role of a smoothening factor. For most cases, reasonable results are obtained for the exponent value between 2.0 (default) and 3.0. For big exponent values, the algorithm converges with the Voronoi diagram.
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 the best possible results. The Radius property is the size of the window in map units.
Pros
- good for interpolating data with extreme value changes at short distances
- gives intuitive results for clusters of points with small value variation
Cons
- interpolated values do not exceed the range of minimum to maximum values of the input data
- not good for mountain-like areas, because it flattens peaks