Grid Tools: Secondary Estimates

Secondary estimates, used to determine Z values at any grid nodes not assigned a value during primary estimates, are applied when using the Radial Search and Radial Search (Clustered) algorithms, and are sometimes applied when the Weighted Resampling algorithm does not return a value at each node during primary estimates.

Secondary estimates are formed only at those nodes that qualify based on their distance from a primary estimate, and the distribution of any surrounding nodes that have been assigned values. Distance has a major effect on the coverage generated. Using a small distance, equal to the grid interval, avoids the calculation of secondary estimates. The number of empty octants allowed also has a major affect on the resulting coverage. Allowing empty octants of 4 or 5 permits extrapolation beyond the limits of the point set coverage area.

Each qualified node is calculated by fitting the surrounding valued nodes to a plane then weighting all points by their relative distance from the node to be calculated. This process is stabilized by computing nodes adjacent to a node that already has a value. Multiple passes over the entire grid range expands the number of grid values about the primary estimates robustly.