[postgis-users] Center of Points

[Paul Ramsey]

Since you are just dealing with points, it is far more effective to  
calculate this *outside* the spatial domain.

SELECT makepoint(avg(x(the_geom)),avg(y(the_geom))) FROM thetable  
WHERE <theclause> GROUP BY <thegroup>

P.

On 9-Mar-06, at 6:44 AM, Stephen Woodbridge wrote:

> This works for me on:
>
> "POSTGIS="1.1.1" GEOS="2.2.1-CAPI-1.0.1" USE_STATS", "POINT 
> (-47.3229673751195 -22.7344596651925)",
> "POINT(-47.3570658875554 -22.6784457605688)"
>
> -Steve
>
> Jens Werdin wrote:
>> This is my version:
>> POSTGIS="1.1.0" GEOS="2.2.1-CAPI-1.0.1" PROJ="Rel. 4.4.9, 29 Oct  
>> 2004" USE_STATS
>> Am Donnerstag, 9. März 2006 14:42 schrieb Gustavo Henrique Sberze  
>> Ribas:
>>> Hallo,
>>>
>>>
>>>> I'm using postgis 1.1.0 on a postgres 8.1.2.
>>>> if i'm using your query as it is, i'm getting POINT(nan nan) too.
>>>
>>>  Well, I've forgot to include commas to separate the points. This
>>> wasn't an issue with PostGIS 0.9 but version 1.0 complained about  
>>> it.
>>> Anyway, I've tested it against the versions I had available:
>>>
>>> POSTGIS="1.0.1" GEOS="2.1.1" PROJ="Rel. 4.4.9, 29 Oct 2004"  
>>> USE_STATS
>>> DBPROC="0.3.0" RELPROC="0.3.0" PostgreSQL 8.0.3
>>> and
>>> POSTGIS="0.9.0" GEOS="2.0.1" PROJ="Rel. 4.4.8, 3 May 2004" USE_STATS
>>> DBPROC="0.0.1" RELPROC="0.0.1" PostgreSQL 8.0.0
>>>
>>> both worked. Perhaps there's something wrong with your installation?
>>>
>>>
>>>> if i'm adding a convexhull on the geomcoll I get a POINT, but
>>>> i think it is the center of the hull and not the center of the  
>>>> points.
>>>
>>> You're right. Just in case you're curious (I was) the green point  
>>> in the
>>> attached picture shows the convex hull's centroid. The numeric  
>>> results
>>> are
>>>  pointscentroid = POINT(-47.3229673751195 -22.7344596651925)
>>>  convexhullcentroid  = POINT(-47.3570658875554 -22.6784457605688)
>>> the query I used is attached below.
>>>
>>> Servus,
>>> Gustavo
>>>
>>> --
>>>
>>> select asText(centroid(geomCollFromText('GEOMETRYCOLLECTION(
>>> POINT(-47.2412222222222 -22.7405833333333),
>>> POINT(-47.3199166666667 -22.7333333333333),
>>> POINT(-47.3545555555556 -22.7443055555556),
>>> POINT(-47.3008346557617 -22.7133331298828),
>>> POINT(-47.3302764892578 -22.731388092041),
>>> POINT(-47.3406111111111 -22.76525),
>>> POINT(-47.29525 -22.7161388888889),
>>> POINT(-47.3481666666667 -22.7247222222222),
>>> POINT(-47.3160277777778 -22.7383888888889),
>>> POINT(-47.3275 -22.7459722222222),
>>> POINT(-47.34025 -22.7523333333333),
>>> POINT(-47.3368988037109 -22.7385997772217),
>>> POINT(-47.3527793884277 -22.7352771759033),
>>> POINT(-47.3476388888889 -22.7324444444444),
>>> POINT(-47.3481666666667 -22.7247222222222),
>>> POINT(-47.2624722222222 -22.7496944444444),
>>> POINT(-47.34025 -22.7523333333333),
>>> POINT(-47.3160277777778 -22.7383888888889),
>>> POINT(-47.3406111111111 -22.76525),
>>> POINT(-47.3275 -22.7459722222222),
>>> POINT(-47.3001944444444 -22.7144444444444),
>>> POINT(-47.3520555555556 -22.7320277777778),
>>> POINT(-47.2952222222222 -22.7311111111111),
>>> POINT(-47.3071944444444 -22.7513888888889),
>>> POINT(-47.2978611111111 -22.7079722222222),
>>> POINT(-47.3025833333333 -22.7260555555556),
>>> POINT(-47.3317777777778 -22.7485),
>>> POINT(-47.2861111111111 -22.7694444444444),
>>> POINT(-47.2861111111111 -22.7722222222222),
>>> POINT(-47.2944444444444 -22.775),
>>> POINT(-47.2861111111111 -22.7805555555556),
>>> POINT(-47.5083333333333 -22.5055555555556))',4326))) as  
>>> PointsCentroid
>>> ,asText(centroid(convexhull(geomCollFromText('GEOMETRYCOLLECTION(
>>> POINT(-47.2412222222222 -22.7405833333333),
>>> POINT(-47.3199166666667 -22.7333333333333),
>>> POINT(-47.3545555555556 -22.7443055555556),
>>> POINT(-47.3008346557617 -22.7133331298828),
>>> POINT(-47.3302764892578 -22.731388092041),
>>> POINT(-47.3406111111111 -22.76525),
>>> POINT(-47.29525 -22.7161388888889),
>>> POINT(-47.3481666666667 -22.7247222222222),
>>> POINT(-47.3160277777778 -22.7383888888889),
>>> POINT(-47.3275 -22.7459722222222),
>>> POINT(-47.34025 -22.7523333333333),
>>> POINT(-47.3368988037109 -22.7385997772217),
>>> POINT(-47.3527793884277 -22.7352771759033),
>>> POINT(-47.3476388888889 -22.7324444444444),
>>> POINT(-47.3481666666667 -22.7247222222222),
>>> POINT(-47.2624722222222 -22.7496944444444),
>>> POINT(-47.34025 -22.7523333333333),
>>> POINT(-47.3160277777778 -22.7383888888889),
>>> POINT(-47.3406111111111 -22.76525),
>>> POINT(-47.3275 -22.7459722222222),
>>> POINT(-47.3001944444444 -22.7144444444444),
>>> POINT(-47.3520555555556 -22.7320277777778),
>>> POINT(-47.2952222222222 -22.7311111111111),
>>> POINT(-47.3071944444444 -22.7513888888889),
>>> POINT(-47.2978611111111 -22.7079722222222),
>>> POINT(-47.3025833333333 -22.7260555555556),
>>> POINT(-47.3317777777778 -22.7485),
>>> POINT(-47.2861111111111 -22.7694444444444),
>>> POINT(-47.2861111111111 -22.7722222222222),
>>> POINT(-47.2944444444444 -22.775),
>>> POINT(-47.2861111111111 -22.7805555555556),
>>> POINT(-47.5083333333333 -22.5055555555556))',4326)))) as  
>>> ConvexHullCentroid
>
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