[postgis-users] ST_DWithin advice

[a wright]

Brigit,

Thank you so much for the response. I implemented a temporary workaround at
the Java application layer. But, I'll definitely take a look at your idea

-Adam


On Fri, Jun 13, 2014 at 8:24 AM, Birgit Laggner <birgit.laggner at ti.bund.de>
wrote:

>  Hi Adam,
>
> perhaps you could solve the problem with this workaround:
>
> 1. Transform pt1 into geometry data type with srid 4326 (coordinates are
> in degrees, now)
> 2. Create a new point by shifting pt1 for # degrees in x-direction
> 3. Create a linestring geometry by connecting pt1 and the new point
> 4. Transform the linestring back into geography data type
> 5. Calculate length of linestring in meters
> 6. Use length in meters for definition of the ST_DWithin radius
>
> It's a little bit complicated and maybe you came up with a better idea in
> the meantime...
>
> Regards,
>
> Birgit.
>
>
>
> Am 02.06.2014 20:58, schrieb Adam Wright:
>
>  We have several tables with latitude and longitude columns (data type:
> numeric) and I need to calculate whether a given lat/lon is within #
> degrees of a point-radius ring. I came up with the function below. The user
> supplied radius has to be in degrees (e.g. give me all records within 5 to
> 25 degrees of this lat/lon pair). Sample query:  select * from mytable
> where
> dist_check(mytable.latitude.mytable.longitude,35.6895,139.6917,5,25)=1.
>
>  Any advice on solving the same problem using the geography data type
> when the input radius is supplied in degrees?
>
>  CREATE OR REPLACE FUNCTION dist_check(lat1 numeric, lon1 numeric, lat2
> numeric, lon2 numeric, innerradius numeric, outerradius numeric)
>
> pt1 geometry;
> pt2 geometry;
> BEGIN
> pt1 := ST_MakePoint(lon1,lat1);
> pt2 := ST_MakePoint (lon2,lat2);
> IF ST_DWithin(pt1,pt2,outerRadius) AND NOT ST_DWithin(pt1,pt2,innerRadius)
> THEN return 1;
> ELSE
> return 0;
> END IF;
>
>  Thanks!
>
>
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