[postgis-users] How to get the distance between geometry in meters?

[R H]

isn't this the same as putting two geom w/ a meter projection into st_distance(), st_distance() still returns a cartesian distance not a distances in meters?  Wouldn't you need to do something like...
transform(st_distance(geom,geom),srid)???  
 
I only ask because I am having a simular problem.  My projections are in a meter projection, but I can't get st_distance() or st_dwithin() to use meters?  any thoughts?


Subject: RE: [postgis-users] How to get the distance between geometry in meters?Date: Wed, 19 Mar 2008 06:56:24 -0400From: robe.dnd at cityofboston.govTo: postgis-users at postgis.refractions.net

You'll need to transform to a meter based projection to do that.  If for example you are in the U.S, SRID 2163 US National Atlas Equal Area works pretty good for measurement.  It is not as accurate as UTM or State Plane, but its pretty good and covers all of US I believe and probably works for some of Canada as well (not sure about non-continental e.g. Hawaii, Alaska).  
 

e.g.
 
SELECT road.rd_name, ht.ht_name, ST_Distance(ST_Transform(roads.the_geom,2163) , ST_Transform(hotel.the_geom,2163))  as dist_meters
FROM road, hotel
WHERE <some criteria here>
 
If you are somewhere else and your locations are within that projection, you can use that.  Look at the utmzone function in the wiki that will help you determing the right UTM zone SRID for your data
 
http://postgis.refractions.net/support/wiki/index.php?plpgsqlfunctions
 
So you would use something liek
SELECT utmzone(ST_Centroid(the_geom)) as srid
 
to get the right UTM zone SRID
 
 
Hope that helps,
Regina
 
 



From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Sinboy ChangSent: Wednesday, March 19, 2008 3:09 AMTo: postgis-users at postgis.refractions.netSubject: [postgis-users] How to get the distance between geometry in meters?

i want to get the distance between geometry,just like road or hotel poi,but ST_Distance() return the result in cartesian dintance.
So how can get the distance() by meters?




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