[postgis-users] Finding Points with distance to a location.

[Brad Ediger]

You want to use the Distance function in the result set:

SELECT location_id, Distance(point_geom, MakePoint(-117.13538,  
32.6857)) FROM table;

You don't need a WHERE clause unless you want to restrict the result  
rows (for example, if you wanted to limit the results to locations  
within 50 miles of the target point).

I would suggest reviewing the PostgreSQL documentation for some basic  
SQL instruction (at http://www.postgresql.org/docs/; the manual is  
actually very good). Then you can refer to the PostGIS reference  
(http://postgis.refractions.net/docs/ch06.html) for a list of functions.

You really don't need a lot of knowledge on top of PostgreSQL to use  
PostGIS effectively. Most everything that seems confusing or vague  
about the PostGIS documentation can be clarified by reading the  
OpenGIS specs, at http://www.opengeospatial.org/standards/sfa and  
http://www.opengeospatial.org/standards/sfb.

And you can always ask on postgis-users if you need clarification.

Hope this helps,
Brad

On Dec 30, 2006, at 12:10 AM, Adam wrote:

> I've tried:
>
> SELECT point_geom, location_id
> FROM locations
> WHERE Distance(point_geom, 'POINT(-117.13538 32.6857)')
> But get error:  argument of WHERE must be type boolean, not type  
> double precision
>
>
> ----- Original Message -----
> From: Adam
> To: PostGIS Users Discussion
> Sent: Saturday, December 30, 2006 12:07 AM
> Subject: [postgis-users] Finding Points with distance to a location.
>
> I figured this out last year, but can't figure out how I figured it  
> out.  I've read "Mapping Hacks" and "Web Mapping Illustrated" along  
> with what I could find in the WIKI and documentation but can't  
> start to figure it out.
>
> I have my geometry column named "point_geom" and a unique column  
> named "location_id".
>
> I want to query the distance of all the points in my "point_geom"  
> column to coords:  Long = -117.13538 :: Lat = 32.6857
>
> What would the query for this look like?  Is there a comprehensive  
> article or book out that goes in depth into how spatial queries work?
>
> The output would look like this:
>
> location_id | distance
> -------------------------------
> 5 | 45.38823
> 9 | 50.39952
> 1 | 82.39923
> .
> .
> .
> -------------------------------
>
>
> I'm guessing that you'd use distance_spheroid for the calculation.
>
>
>
>
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