Pitney Bowes MapInfo Vertical Mapper - Manual (Page 41)

Chapter 3: Creating Grids Using Interpolation
User Guide
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The Interpolation Wizard provides two methods of performing natural neighbour interpolation. The
simple option offers the first-time user a two-step process for implementing the interpolation method.
Many of the controls have been pre-set to generate the most appropriate surface given the
distribution of points. The Advanced option enables you to fine-tune the grid surface.
Exploring the Simple Natural Neighbour Interpolation Dialog Box
The Simple Natural Neighbour Interpolation dialog box contains basic settings for building a grid file.
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 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
point file by 500, considered an optimum number based on the computing power required to solve
this algorithm.
The Aggregation Distance box enables you to define the minimum separation allowed between
data points before aggregation of the points is initiated. The aggregation technique makes use of the
Forward Stepping method (see
Forward Stepping Aggregation on page 180 ) where the
aggregation distance is the radius of circular search zones centred on successive points in the data.
Data points that fall within this search zone are mathematically averaged, and a new data point is
placed at the geometric centre of the aggregated points. Aggregation is a useful method for quickly
grouping points that may be virtually coincident. It is also used as a preliminary data smoothing
technique where highly variable data points that are spaced closely together can be aggregated and
new values calculated using averaging. If no aggregation is desired, set this value to zero. By
default, the aggregation distance is set at 10 percent of the mean distance between the data points.
The Surface Solution Type section contains three options that are used to control the degree of
smoothness applied to the new interpolated grid and refer to the different variations of the natural
neighbour algorithm available.
• The Linear option calculates the value of a grid node using the average value of the surrounding
points. The calculation is area-weighted to account for the relative influence of the surrounding
points. The Linear Solution produces a profile that is slightly smoother than the constant value
solution available with natural neighbour interpolation.