Pitney Bowes MapInfo Vertical Mapper - Manual (Page 51)

Chapter 3: Creating Grids Using Interpolation
User Guide
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Exploring the Kriging: Interpolation Dialog Box
The Kriging Interpolation dialog box enables you to set a number of user-defined parameters.
The Cell Size (lag distance) box enables you to set the cell size in real units. The grid dimensions (in
cell units) vary inversely with cell size: the smaller the cell, the larger the grid file. The value chosen
here should be a compromise between the degree of resolution required for analysis and
visualization purposes and the processing time and file size. The default value is calculated by
dividing the diagonal width of the aggregated point file by 250, considered an optimum number
based on the computing power required to solve this computationally intensive algorithm.
The Search Radius box enables you to define the maximum size, in map units, of a circular zone
centred on each grid node within which point values from the original data will be used in the
calculation. You can also define the minimum and maximum number of data points in the Search
Criteria section. The default setting is calculated as the diagonal distance through the minimum
bounding rectangle of the point data. This setting will automatically change based on the results of
the semivariogram analysis. The analysis is performed when you click the Variogram Builder button.
The Minimum # of Points and Maximum # of Points lists enable you to set the minimum number
of points that must be found inside the search radius in order to assign a calculated value to a grid
node, and the maximum number of points that will be used in the calculation. The default values of
three and 10 respectively are appropriate for most data. You must keep in mind that if the maximum
number of points in this setting is doubled, the processing time will increase by a factor of eight.
The Set button enables you to choose one of three different types of kriging: ordinary kriging, simple
kriging, and universal kriging. The default method is set to ordinary kriging which is suitable for most
data. Regardless of the kriging type employed, block kriging can also be implemented.
The Variogram Builder button enables you to build a semivariogram of the data, enabling you to
match or tune a mathematical model to the experimental semivariogram. For more information, see
Semivariogram Analysis on page 156 and Exploring the Variogram Dialog Box on page 161 .
The File name box enables you to enter the file path and name of the new grid that will be created.
With the kriging interpolation technique, two grids are created. The first is the interpolated surface
grid and the second is a grid of the estimated variance at each grid cell. The variance grid will have
the same file name as the surface grid but will have “_var” appended to the end of the name. Both
grids are placed in the same folder.