Explication http://a.mongers.org/clueful/20020402-peopleware-blackteam
On Thu, Apr 22, 2010 at 10:48 AM, Paul Ramsey <[email protected]> wrote: > You're such a Black Team member, Regina :) > I think the geography spheroid calculation falls back to a sphere > calculation if it is handed the 180 case, and probably the 180 degree > test is sufficiently fuzzy that it is picking up "pretty close" > results. > Worth a ticket, I'm sure we can make things a bit more consistent, for > the geography type too. > > P > > On Thu, Apr 22, 2010 at 10:24 AM, Paragon Corporation <[email protected]> wrote: >> Also not entirely true. >> >> If we set to 179.9999 >> >> Answers are different >> >> Though 179 they are the same >> >> SELECT st_distance_spheroid(geomfromtext('POINT(0 0)',4326), >> geomfromtext('POINT(179 >> 0)',4326),'SPHEROID["WGS84",6378137,298.257223563]'); >> >> On 1.5 - 19926188.8494779 >> >> On 1.4 - 19926188.851996 >> >> However: >> >> SELECT st_distance_spheroid(geomfromtext('POINT(0 0)',4326), >> geomfromtext('POINT(179.999 >> 0)',4326),'SPHEROID["WGS84",6378137,298.257223563]'); >> On 1.4 - 20037397.0232984 >> On 1.5 - 19903482.0714439 >> -----Original Message----- >> From: [email protected] >> [mailto:[email protected]] On Behalf Of Paragon >> Corporation >> Sent: Thursday, April 22, 2010 1:18 PM >> To: 'PostGIS Users Discussion' >> Subject: Re: [postgis-users] ST_length_spheroid and ST_distance_spheroid >> >> I think it's a difference in versions >> >> On our PostGIS 1.4 windows the answers are the same (note Paul was showing a >> 1.4 answer I presume from his command prompt) >> >> On our PostGIS 1.5 its different. >> >> I suspect its because in >> >> PostGIS 1.5 the distance_spheroid piggy backs on the geography support to >> support more than just points. >> >> I suspect the length_spheroid logic wasn't changed to do the same which is >> why it gives the same answer as 1.4 >> >> Hope that helps, >> Regina and Leo >> http://www.postgis.us >> >> >> >> -----Original Message----- >> From: [email protected] >> [mailto:[email protected]] On Behalf Of Olivier >> Courtin >> Sent: Thursday, April 22, 2010 1:07 PM >> To: PostGIS Users Discussion >> Subject: Re: [postgis-users] ST_length_spheroid and ST_distance_spheroid >> >> >> On Apr 22, 2010, at 6:54 PM, Paul Ramsey wrote: >> >>> If you change the 180 to 179 do the results match up again? (ie, do >>> any distance less than a perfect half-sphere?) >> >> Yes, right assertion. >> Values are the same below 180 >> >> -- >> Olivier >> >> >> >> _______________________________________________ >> postgis-users mailing list >> [email protected] >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> >> >> _______________________________________________ >> postgis-users mailing list >> [email protected] >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> >> >> _______________________________________________ >> postgis-users mailing list >> [email protected] >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> > _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
