[mlpack] Numeric sensitivity of RangeSearch

[Li Dong]

Dear all,

I have used RangeSearch to search neighbours on the sphere surface. Previously, the radius of sphere is set to 1, so the Cartesian coordinate range (I convert spherical coordinate to Cartesian coordinate for searching) is from -1 to 1. In real applications, the radius of the Earth is around 6.371e6, and the Cartesian coordinate range is also from -6.371e6 to 6.371e6. The problem that I am facing is when radius is 6.371e6, many neighbours are not found by RangeSearch.

I have uploaded the result comparison in https://gist.githubusercontent.com/dongli/9634592/raw/cb3e6cdf85758594be15fabd7fa61d73ac4ecf3e/rangesearch_numeric_problem.png, where the blue circle represents the range (approximately), and red points are the neighbours. The only difference is the radius.

Any idea? Thanks in advance!

Best regards,

-----------------------------------------
Dr. Li Dong (董理)
LASG, Institute of Atmospheric Physics
Chinese Academy of Sciences
P.O. Box 9804
Beijing 100029, China
Phone: 8610-8299 5143

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