[postgis-users] ST_Buffer questions

[Chen, Li [Contractor]]

Hi,

Do you might know a proper "appropriate_projection_epsg"? I am in Australia but I might need to use data from the whole world.

Also, I was not able to find a SRID for ECEF reference system, does anyone know?

Thanks,

Li

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Ben Madin
Sent: Thursday, 1 April 2010 4:42 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] ST_Buffer questions

G'day Li,

I can't help with Q2, but

On 01/04/2010, at 12:28 , Chen, Li [Contractor] wrote:

> Q1.
> ST_Buffer(g1, range) is able to return a geometry within the range of g1.
>  
> So, I define two point using lon/lat (SRID=4326) and range 10km. I want to see whether they cross each other by using ST_Crosses(g1, g2).
> However, I don't know the unit of the range parameter in ST_Buffer(g1,range)  as it is not provide in the docs. So is it km or meters?

The same unit as your Geometry - decimal degrees. Obviously due to the change in the value of this unit at differing latitudes, this is not useful, so a more sensible approach is either to transform your point into a projection using metres, and then use metres

 (off the top of my head it would look like :

select st_buffer(st_transform(g1, appropriate_projection_epsg),10000);

but you should check the docs)

or use the geography type from postgis 1.5? but I haven't tried it yet?

cheers

Ben

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