Pitney Bowes MapInfo Vertical Mapper - Manual (Page 44)

Natural Neighbour Interpolation
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Vertical Mapper 3.7
Quantitatively, if the proportional natural neighbour area of a point is greater than 50 percent of the
total grid node natural neighbour area, the Hermitian curve applies greater weight to this point. If the
proportional natural neighbour area of a point is less than 50 percent of the total grid node natural
neighbour area, the Hermitian curve applies lower weight to this point.
The Weight Factor box enables you to define the degree of influence imposed by neighbouring
triangles in calculating a slope value for each data point. This is used only in the slope-based
method of natural neighbour interpolation. Increasing the weighting factor will increase the relative
influence of more distant data points.
The Exponent box enables you to set a variable, when calculating a slope value for each data point
for the slope-based solution, that defines the exponential decay of influence by neighbouring points
that lie farther from each point. Increasing the exponent will decrease the relative influence of more
distant points.
The Allow Overshoot/Undershoot check box enables you to set the slope so that you can see
values in the newly interpolated grid that exceed the range of the original point values.
Exploring the Natural Neighbour: Interpolation Dialog Box
After you have made the necessary adjustments to the grid surface in the Advanced Natural
Neighbour Interpolation dialog box, you need to set a number of general parameters that control the
grid building process.
The Boundary Type section refers to the selection of a hull that controls the outward extent of
interpolation and forms the outermost boundary of the grid file. Two choices are available.
• The Convex Hull option enables you to set the natural boundary of the data defined by the
outermost extent of the points. When you choose this option, the Hull Boundary Width and
Corner Increment boxes become available.
• The Pick Region from MapInfo Table option enables you to choose a pre-defined MapInfo
region as the point boundary. When you click the Finish button, you are prompted to pick a
MapInfo table as a boundary region.
The Cell Size 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