(from pysal/network) add option for approximate point snapping to network #650

[jGaboardi]

pysal/pysal#650

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Current implementation is exact, but crawls when the network gets large. Adding an option to approximation which only uses the kd-tree for the segment nodes might be a compromise.

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In addition, we might look at swapping the current rtree implementation for a cython implementation. Could test, against the current implementation, for speed and accuracy of these different methods.

[jGaboardi]

Here, I think it may be a good compromise for "approximate" point snapping to be realized as snapping to network nodes, not the along the lines themselves.

[jGaboardi]

The is exactly related to #76