Re: Earth distance

So does Postgres do 'Great Circle' calculations? Like distance between two
points? What dataset does it use?

Tad Marko wrote:
> On Thu, 2003-03-27 at 08:40, Stephan Szabo wrote:
>
>>On Thu, 27 Mar 2003, Bruno Wolff III wrote:
>>
>>
>>>On Wed, Mar 26, 2003 at 18:29:42 -0600,
>>> Tad Marko <tad(at)tadland(dot)net> wrote:
>>>
>>>>Bruno,
>>>>
>>>>I aplogize for bothering you direclty, but I'm having some difficulty with
>>>>some syntax using the earth distance functions. Every single example I can
>>>>find is using hard coded constants for the latitude and longitude, but I'm
>>>>trying to use a join to get these values. Basically, what I'm trying to do
>>>>is:
>>>>
>>>>select up.first_name, up.last_name, up.city, zip_code from user_primary as
>>>>up, ziplocs as zl where zl.zip=up.zip_code::integer and '(33.0, 97.1)'::point
>>>><@> '(zl.lat, zl.lon)'::point < 50;
>>>>
>>>>But this fails with a
>>>>
>>>>ERROR: Bad point external representation '(zl.lat, zl.lon)'
>>>>
>>>>message. I simply cannot figure out how to specify the lat and lon values
>>>>from the joined table. Can you offer any suggestions?
>>
>>That'd attempt to make a point from the string literal given, not what you
>>want. I think point(zl.lat, zl.lon) might work (there's a point function
>>that takes two doubles and returns a point).
>
>
> Excellent! That's all I needed. I just hadn't come across the point
> function in the documentation (searching on point yields quite a pile of
> responses at the Postgres site), and I'm starting to doubt the value the
> O'Reilly book on Postgres.
>
> Now all I have to do is figure out how to deal with the issue of
> canadian zip codes that we have mixed in.
>
> Thanks!
>
> Tad
>