[postgis-users] Identity Overlay

[Stephen Woodbridge]

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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