Pitney Bowes MapInfo Vertical Mapper - Manual (Page 43)

Chapter 3: Creating Grids Using Interpolation
User Guide
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The Extents button displays a summary of the geographic size and the z-value range of the original
point database, the density of the points, and the data value units.
Exploring the Natural Neighbour: Solution Method Dialog Box
The final step in the Advanced Natural Neighbour technique involves choosing the solution method
and setting a number of interpolation parameters.
The Constant option enables you to assign the exact value of the underlying natural neighbour
region to the new grid node. The resulting grid is a very close approximation of the natural neighbour
region map (Voronoi diagram) that can be generated from the original data points.
The Linear option enables you to assign the average z-value of each surrounding point weighted
according to the area that is encompassed by a temporary natural neighbour region generated
around the grid node.
The Slope option enables you to assign the area-weighted average slope of each surrounding point.
By examining the adjacent points, a determination is made as to whether that point represents a
local maximum or minimum value. If it does, a slope value of zero is assigned to that value, and the
surface will honour that point by neither overshooting nor undershooting it.
The Skewness Factor box enables you to define a weighting factor used in the grid node
calculation that can be used to assign greater or lesser influence to the data point that is closest to
the grid node, such as the point whose natural neighbour area directly underlies the grid node.
Allowable values range from 0.001 to 999. If the maximum allowable skewness factor is entered, the
resulting grid will appear very similar to a grid generated using the constant value solution because
the value at each grid node is almost entirely influenced by the point lying nearest to it.
The Hermitian Smoothing check box enables you to apply a weighting curve to the grid node
calculation that effectively assigns greater influence to points that are closer to the grid node based
on their proportionally larger intersecting areas. Conversely, Hermitian Smoothing will assign lower
weighting to points that lie farther from the grid node based on their proportionally smaller
intersecting areas.