[postgis-users] Identity Overlay

[Aaron Koning]

I forgot about the float comparison, so thanks for that pointer.

Great to hear that PIP will be built in. Currently, with a million and half
points it can take a while, but the end result is great!

Aaron

On 11/22/06, Paul Ramsey <pramsey at refractions.net> wrote:
>
> This is such a common performance case, we're going to add some
> automagical code to make Contains() work more efficiently, by
> short-circuiting and Contains(POLYGON, POINT) cases directly to an
> internal postgis PIP algorithm.
>
> P
>
> Stephen Woodbridge wrote:
> > Try:
> >
> > UPDATE point_layer SET b250k_tag = polygon_layer.b250k_tag WHERE
> >   polygon_layer.the_geom && point_layer.the_geom and
> >   distance(polygon_layer.the_geom, point_layer.the_geom) < 0.00001;
> >
> > It is not good to compare floats with equals due to possible rounding
> > errors.
> >
> > -Steve
> >
> > Aaron Koning wrote:
> >> Hi All,
> >>
> >> I am trying to perform an identity overlay where each point in a point
> >> layer gets a value from a polygon layer based on what polygon contains
> >> the point. I have come up with the following query which is working
> >> fairly well.
> >>      UPDATE point_layer SET b250k_tag = polygon_layer.b250k_tag WHERE
> >> contains(polygon_layer.the_geom, point_layer.the_geom);
> >>
> >> I am just wondering if other people have performed identity like
> >> overlays in PostGIS and is there a better / more efficient way to
> >> perform them?
> >>
> >> Thanks,
> >> Aaron
> >>
> >> +-------------------------------------------------
> >> |  Aaron Koning
> >> |  Information Technologist
> >> |  Prince George, BC, Canada.
> >> +-------------------------------------------------
> >> |  Flexible Internet Spatial Template:
> >> |       http://fist-mapping.org
> >> +-------------------------------------------------
> >>
> >>
> >>
> ------------------------------------------------------------------------
> >>
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-- 
+-------------------------------------------------
|  Aaron Koning
|  Information Technologist
|  Prince George, BC, Canada.
+-------------------------------------------------
|  Flexible Internet Spatial Template:
|       http://fist-mapping.org
+-------------------------------------------------
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