Forgot to mention 2163 - my mention of pretty good may not be as good as your idea and my "pretty good" definition actually varies depending on what function I am trying to do. I guess I should have said "May be good enough" rather than pretty good. 2163 will give you a ball park figure (say within a couple meters of accuracy) and the further the geometries are away from each other I think the worse that ballpark figure gets. If you are doing surveying work or launching missiles - 2163 is horrible and you'll want something like UTM or stateplane (basically a conformal projection that covers smaller area). It is all a matter of trade-offs. Hope that helps, Regina
________________________________ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Obe, Regina Sent: Wednesday, March 19, 2008 6:56 AM To: PostGIS Users Discussion Subject: RE: [postgis-users] How to get the distance between geometry inmeters? 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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Sinboy Chang Sent: Wednesday, March 19, 2008 3:09 AM To: [email protected] Subject: [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? ________________________________ The substance of this message, including any attachments, may be confidential, legally privileged and/or exempt from disclosure pursuant to Massachusetts law. It is intended solely for the addressee. If you received this in error, please contact the sender and delete the material from any computer. ________________________________ Help make the earth a greener place. If at all possible resist printing this email and join us in saving paper. ----------------------------------------- The substance of this message, including any attachments, may be confidential, legally privileged and/or exempt from disclosure pursuant to Massachusetts law. It is intended solely for the addressee. If you received this in error, please contact the sender and delete the material from any computer.
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