Topic:
How does the least squares algorithm work in Basemap Plus?

Description:
When gridding in GeoFrame, how does the least squares algorithm calculate the
node values?

Solution:
Least Squares uses a search radius to locate data within a specified distance of
each grid node.  For each node, the data is collected, compared, and weight
averaged based on distance from the node is used to calculate the grid node
value.  No iteration occurs, the final grid size is used throughout the
process.  

The advantages are:
  - it does not extrapolate far from the data
  - it works well for evenly distributed data
  - it produces good estimates of linear models 
  - it does not contour inside fault boundaries.  

Weaknesses include, very time consuming on large data sets, it produces poor
results under conditions of irregularly spaced, sparse data (i.e. 2D seismic),
and when it does extrapolate, the results are poor.



Last Modified on: 11-FEB-99