[postgis-users] Center of Points

[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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