[postgis-users] GeomUnion Bug?

[Charlie Savage]

Hi Carl,

> Charlie ,
> 
> neither of those polygons are valid
> 
> repeating points, self intersecting and the second one is not a closed 
> linestring

Interesting - that is what PostGis/Geos produces when you do this:

select astext(envelope(GeomFromText('POINT(-104 40)')))

"POLYGON((-104 40,-104 40,-104 40,-104 40,-104 40))"

But you are right, PostGis doesn't think they are valid:

select isvalid(envelope(GeomFromText('POINT(-104 40)')))

False

And this did work in older versions of GEOS - maybe it shouldn't have.

So here is my problem then.  I have a map, a user enters a point.  I 
want to store the bounding box.  So I use the envelope function as 
above.  User enters another point.  Find its bounds.  Then union them 
together.  I don't want to recalculate the bounds based on all the 
points each time because its too expensive finding all the constituent 
geometries.

Ideas?

Charlie


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