up previous next
PreprocessPts5

Reduce redundancy in a set of approximate points
Syntax 

PreprocessPts5(Pts: LIST, Toler: LIST): RECORD[Points: LIST, Weights: LIST]
PreprocessPts5(Pts: LIST, Toler: LIST, "Grid"): RECORD[Points: LIST, Weights: LIST]
PreprocessPts5(Pts: LIST, Toler: LIST, "Subdiv"): RECORD[Points: LIST, Weights: LIST]
PreprocessPts5(Pts: LIST, Toler: LIST, "Aggr"): RECORD[Points: LIST, Weights: LIST]

Description
This function is implemented in CoCoALib (requires an active CoCoAServer).

This function returns a record containing two fields Points which is a list of well-separated points, and Weights which contains the number of input points associated to each output point. The first argument is a list of points in k-dimensional space, and the second argument is list of k tolerances (one for each dimension). The function detects groupings of close points, and chooses a single representative for them (which lies within the given tolerance of each original point); the result is the list of these representatives, and the number of original points associated to each representative.

There is a third, optional argument: it should be one of the strings Grid, Subdiv, Aggr and specifies which specific algorithm to use. If there are just two arguments, an automatic choice is made between Subdiv and Aggr; the Subdiv method works well when the original points are densely packed (so the result will be a small list), while the Aggr method is better suited to situations where the original points are less densely packed. The Aggr and Subdiv methods regard the tolerances as being slightly flexible.

For a full description of the algorithms we refer to the paper J.Abbott, C.Fassino, L.Torrente Thinning Out Redundant Empirical Data (arXiv:0702327).



Example 
  Pts := [[-1,0],[0,0],[1,0],[99,1],[99,0],[99,-1]];
  Toler := [3,3];
  PreprocessPts5(Pts, Toler);
Record[Points=[[99, 0], [0, 0]], Weights = [3, 3]]
-------------------------------
  PreprocessPts5(Pts, [0.8,0.8]);
Record[Points = [[-1/2, 0], [1, 0], [99, 1/2], [99, -1]], Weights = [2, 1, 2, 1]]
-------------------------------
  PreprocessPts5(Pts, [0.9,0.9], "Aggr"); -- exhibits tolerance flex
Record[Points = [[0, 0], [99, 0]], Weights = [3, 3]]
-------------------------------


See Also