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

[Brad Ediger]

My bad.

SELECT location_id, Distance(point_geom, SetSRID(MakePoint 
(-117.13538, 32.6857),4326)) FROM locations;
PostGIS does some sanity checks to ensure you're not operating on  
different SRIDs (which would be meaningless). You have to tell  
PostGIS that the point you're creating has SRID 4326 (WGS84). Note  
that SetSRID won't convert a geometry from one SRID to another; you  
need Transform() for that. You're simply tagging that point with the  
4326 SRID.

On Dec 30, 2006, at 12:54 AM, Adam wrote:

> WHen I run: SELECT location_id, Distance(point_geom, MakePoint 
> (-117.13538, 32.6857)) FROM locations;
>
> I get error:  Operation on two GEOMETRIES with different SRIDs
>
> What does that mean?
> ----- Original Message -----
> From: Brad Ediger
> To: PostGIS Users Discussion
> Sent: Saturday, December 30, 2006 12:49 AM
> Subject: Re: [postgis-users] Finding Points with distance to a  
> location.
>
> 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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>
>
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