[postgis-users] How to add circle to Postgis database?

[Brad Ediger]

On Mar 7, 2007, at 1:36 PM, Jeremy Dunck wrote:

> On 3/7/07, Brad Ediger <brad at bradediger.com> wrote:
>> On Mar 7, 2007, at 12:59 PM, Brent Wood wrote:
> ...
>> > There is unfortunately a nasty trap here, as the point will need  
>> to be
>> > reprojected to a suitable equidistant or equal area projection to
>> > generate a
>> > true circle, ...
>
>> (SRID 27582 is a Lambert II planar projection, as measured in  
>> meters.)
>>
>> CREATE OR REPLACE FUNCTION circle(geometry, numeric) RETURNS geometry
>>      AS 'SELECT Transform(SetSRID(Buffer(Transform(SetSRID($1, 4326),
>> 27582), $2), 27582), 4326);'
>>    LANGUAGE sql;
>
> Hmm, if I understand correctly, Lambert is conformal, which doesn't
> fit the  criteria suggested by Brent (i.e. equidistant or equal-area).
>
> I'm a newbie at this stuff, so it's fairly likely I'm missing  
> something.  :-/
>
> I'm jumping in here because I have the same desire to use a circle
> around a given point.  Cheers for the pointers so far!

OK, you got me. On two counts:

1) I didn't fully read the original post, and
2) I'm a programmer, not a cartographer.

Well, you learn something new every day. I think Lambert II is  
conformal, so that wouldn't help the OP. But aren't there equal-area  
(azimuthal and cylindrical) Lambert projections as well? I defer to  
someone who has real experience in geodesy, rather than my pretend  
experience. :-)

be
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