The CoKriging operation can be directly executed by typing one of the following expressions on the command line of the Main window:
OUTMAP |
= |
MapCoKriging(InputPointMapPred, InputPointMapCovar, Georef, SemiVarModelPred, SemiVarModelCovar, CrossVarModel, LimDist) |
OUTMAP |
= |
MapCoKriging(InputPointMapPred, InputPointMapCovar, Georef, SemiVarModelPred, SemiVarModelCovar, CrossVarModel, LimDist, 1 | 0) |
OUTMAP |
= |
MapCoKriging(InputPointMapPred, InputPointMapCovar, Georef, SemiVarModelPred, SemiVarModelCovar, CrossVarModel, LimDist, 1 | 0, min, max) |
OUTMAP |
= |
MapCoKriging(InputPointMapPred, InputPointMapCovar, Georef, SemiVarModelPred, SemiVarModelCovar, CrossVarModel, LimDist, 1 | 0, min, max, No | Average | Firstval) |
OUTMAP |
= |
MapCoKriging(InputPointMapPred, InputPointMapCovar, Georef, SemiVarModelPred, SemiVarModelCovar, CrossVarModel, LimDist, 1 | 0, min, max, Average | Firstval, Tolerance) |
OUTMAP |
= |
MapCoKriging(InputPointMapPred, InputPointMapCovar, Georef, SemiVarModelPred, SemiVarModelCovar, CrossVarModel, LimDist, 1 | 0, min, max, Average | Firstval, Tolerance, plane | sphere) |
where:
OUTMAP |
is the name of the output raster map. |
MapCoKriging |
is the command to start the CoKriging operation. |
InputPointMapPred |
is the name of the input point map with the predictand (value domain) that is poorly sampled. |
InputPointMapCovar |
is the name of the input point map with the covariable (value domain) that is well sampled. |
Georef |
is the name of an existing georeference for the output raster map. |
SemiVarModelPred |
Model(nugget, sill, range) | Power(nugget, slope, power) This expression defines the semi-variogram model and its parameters that should be used for the predictand. |
SemiVarModelCovar |
Model(nugget, sill, range) | Power(nugget, slope, power) This expression defines the semi-variogram model and its parameters that should be used for the covariable. |
CrossVarModel |
Model(nugget, sill, range) | Power(nugget, slope, power) This expression defines the cross-variogram model and its parameters that should be used. |
Model |
Spherical | Exponential | Gaussian | Wave | RatQuad | Circular |
nugget |
value for the nugget, according to each semi- or cross-variogram (real value). |
sill |
value for the sill, according to each semi- or cross-variogram (real value). |
range |
value for the range, according to each semi- or cross-variogram (real value > 0). |
slope |
when using the Power model: value for the 'slope'. When pow is specified as 1 (i.e. thus using a linear model), then slope is the direction coefficient, i.e. Dg/Dh (real value >= 0). |
pow |
when using the Power model: an exponent 0 < real value < 2. When you use value 1, the Power model will become linear and the slope will be constant. If the power exponent is 2 the assumed stochastic model (‘randomness’) is not always justifiable and the interpolation can become pathological. |
LimDist |
a value for the limiting distance: points that are further away from an output pixel than the limiting distance will not be used in the Kriging equations. Normally, this is a value smaller than the range of the predictand semi-variogram model (0 <= real value < diagonal size of map). |
1 | 0 |
Specify whether or not an error map has to be created. The error map will contain the square root of the Kriging error variance values, i.e. standard deviations per pixel. When this parameter is not specified, no error map will be created. |
1 |
Create an error map. The error map will obtain the same name as specified for the output Kriging map followed by the additional string _Error. |
0 |
Do not create an error map. |
min, max |
Optional parameters (integer values) to specify the minimum and maximum number of points that should be taken into account per Kriging estimate/prediction, i.e. the number of points within the limiting distance of an output pixel that should be taken into account in the calculation of the output value for that pixel.
|
No | Average | Firstval |
|
|
Choose how handle possible coinciding points or duplicates should be handled. When no method is specified, Average will be used. |
No |
No removal of duplicates. Mind: when there are coinciding points, the Kriging system may become unsolvable and will give undefined values for the pixels for which coinciding points are found. |
Average |
Values of duplicates are replaced by the average (arithmetic mean); the coordinates of the first point are taken as new position. |
Firstval |
Values of duplicates (and their coordinates) are replaced by those of the first point. |
Tolerance |
Optional parameter to specify the distance within which 2 sample points are considered to coincide. When not specified, a tolerance of 0.1 m will be used. |
plane | sphere |
optional parameter to calculate distances in a plane (plane), or on the sphere by using the projection of the coordinate system as used by the georeference of the output raster map (sphere). If not specified, distances will be calculated in a plane. |
When the definition symbol = is used, a dependent output map is created; when the assignment symbol := is used, the dependency link is immediately broken after the output map has been calculated.
Example:
The following expression:
OutCoKr |
= |
MapCoKriging (MyPoints.MyAttrA, MyPoints.MyAttrB, MyGeoref, Spherical(10,70,800), Gaussian(30,80,1000), Power(20,40,2), 200, 1, 6, 20, Firstval, 0.2) |
performs CoKriging:
The results of the expression are:
See also: