Re: KD Tree with great circle distances

Hi Ashwin,

If you are using the whole globe, you might want to consider using
something like a VP-tree instead.  A KD-tree needs left/right to be
defined, which you can't do on a sphere.

Scikit-learn has a BallTree, which you can use with a 'haversine' distance
metric, which should allow you to do do nearest neighbours on a sphere

http://scikit-learn.org/stable/modules/generated/sklearn.neighbors.BallTree.html

Hope that helps,
Ed


On 20 May 2018 at 17:49, ashwin .D <[email protected]> wrote:

> Hi David,
>                 Many thanks for your prompt response and that maybe the
> route that I may have to take eventually. I was just wondering whether
> scipy has any equivalent for the stuff described in this paper -
> http://www.soest.hawaii.edu/wessel/sphspline/Wessel+Becker_2008_GJI.pdf ?
>
> Regards,
> Ashwin.
>
> On Sun, May 20, 2018 at 9:56 PM, David Hoese <[email protected]> wrote:
>
>> Hi Ashwin,
>>
>> As far as I know this is the easiest way to do it. I'm not a scipy
>> developer, but you may be interested in the pyresample package:
>>
>> http://pyresample.readthedocs.io/en/latest/
>>
>> Which uses the pykdtree library:
>>
>> https://github.com/storpipfugl/pykdtree
>>
>> And can perform resampling of irregularly spaced data. For certain
>> calculations/utilities it will also convert to XYZ space as described in
>> that SO answer. Hope this helps a little, sorry if it isn't the answer
>> you're looking for.
>>
>> Dave
>>
>>
>> On 5/20/18 11:09 AM, ashwin .D wrote:
>>
>>> Hello,
>>>             I am using - https://docs.scipy.org/doc/sci
>>> py/reference/generated/scipy.spatial.KDTree.html#scipy.spatial.KDTree
>>> which  I believe is using Euclidean distances underneath the hood. But I
>>> want to be able to use great circle distances. Is this the only way to do
>>> this - https://stackoverflow.com/questions/20654918/python-how-to-s
>>> peed-up-calculation-of-distances-between-cities or is there some way I
>>> can extend that class to use great circle distances(maybe somebody has
>>> already done that ? ) I have a irregular shaped grid in a WGS 84
>>> ellipsoid(can be assumed to be a sphere) and so I want to use great circle
>>> distances or if somebody can convince me not to that would be great as well.
>>>
>>>
>>> Best regards,
>>> Ashwin.
>>>
>>>
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