[postgis-users] Calculate variance of a multipoint

[Aren Cambre]

Did anyone have thoughts on this? :-)

Aren

On Wed, May 4, 2011 at 2:12 PM, Aren Cambre <aren at arencambre.com> wrote:

> The more I think about it, is this a job for R? I know I need to start
> using R at some point, just haven't begun yet.
>
> Aren
>
>
> On Wed, May 4, 2011 at 1:42 PM, Aren Cambre <aren at arencambre.com> wrote:
>
>> Suppose you have a geometry type with a multipoint. How would you
>> calculate the variance of the points in that multipoint?
>>
>> I looked through the PostGIS 1.5 function reference and am not coming up
>> with any easy way.
>>
>> A hard way seems to be using st_centroid(multipoint) to find the
>> multipoint's  center. From there, I can calculate the distance of each point
>> from its center, and use that towards calculating the variance (each
>> distance is squared, all squared distances are added together, then divide
>> by number of points).
>>
>> I guess my ultimate need is to measure relative dispersion of multipoints.
>> The multipoints that have the most dispersion are suspect, but I need a way
>> of identifying which ones are like this.
>>
>> Aren
>>
>
>
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