[postgis-users] degrees between points

[Nicholas Lan]

I was under the impression that using srid 4326 meant that point coordinates
would correspond to latitude and longitude on a spheroid such that
st_distance(...) between two such points would give the angle between them,
hence 90 in this case. As you say, st_distance is treating these points as
cartesian coordinates, giving 127. I guess I've got the wrong idea
somewhere.

Regards
Nicholas Lan
  
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-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Chris
Hermansen
Sent: Wednesday, January 16, 2008 5:36 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] degrees between points

Nicholas:

sqrt(90*90 + 90*90) is about equal to 127, as ST_DISTANCE() reports. 
Why are you expecting your distance to be 90?

Nicholas Lan wrote:
>
> Hello,
>
>  
>
> I’m a newbie and have been trying to find the degrees between points
> on a sphere. From reading the documentation I have a table with column
> named “4326” of srid 4326.
>
>  
>
> I insert into this column a point, Geomfromtext(POINT(0 0), 4326)
>
>  
>
> And then doing
>
>  
>
> select ST_DISTANCE("4326",Geomfromtext('POINT(90 90)', 4326)) as dist
> from test3;
>
>  
>
> I expected to see 90 but got 127. What am I doing wrong? Sorry if this
> is a stupid question.
>
>  
>
> Regards
>
> Nicholas Lan
>
>  
>
> ------------------------------------------------------------------------
>
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> postgis-users at postgis.refractions.net
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>   


-- 
Regards,

Chris Hermansen · mailto:clh at timberline.ca
tel:+1.604.714.2878 · fax:+1.604.733.0631
Timberline Natural Resource Group · http://www.timberline.ca
401 · 958 West 8th Avenue · Vancouver BC · Canada · V5Z 1E5

C'est ma façon de parler.

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