I think that you may need to look at using a polar projection to do these types of operations at the poles.
David. On Mon, Sep 28, 2009 at 8:51 AM, Brian Modra <[email protected]> wrote: > 2009/9/28 Brian Modra <[email protected]>: >> 2009/9/28 Malm Paul <[email protected]>: >>> Hi list, >>> I would like to select data over the north pole inside a polygon of lat/lon >>> coordinates >>> For selection I create a polygon from theese coordinates >>> >>> 1) 80, -170 >>> 2) 80, 170 >>> 3) 75, 10 >>> 4) 75, -10 >>> >>> But is seems that the objects found are from around the pole instead of >>> over the pole, it does not find any objects over 80° >>> Is ther a way to get around this? >> >> This is a wild guess, having not looked at the PostGIS code, and not >> knowing how your data is stored, but I wonder if you need to put in >> more coords, because depending on the prjection, the lines joining >> those 4 points could be kind of weird. >> >> e.g. >> 80 0, 80 20, 80 40, 80 50, 80 60... 80 180, 80 -160, 80 -140 ... 80 0 > > Another question for the experts: > what is the inside of the polygon in the above example? Is it above > 80, or below 80, or is the polygon joined up as a straight line at 80 > degrees? I.e. with zero area? > > maybe a better polygon would be: > > 80 -170, 80 -150, 80 -130 ... 80 150, 80 170, 75 170, 75 150, 75 130 > ... 75 -150, 75 -170, 80 -170 > >> >>> Kind regards, >>> Paul >>> _______________________________________________ >>> postgis-users mailing list >>> [email protected] >>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>> >> >> >> >> -- >> Brian Modra Land line: +27 23 5411 462 >> Mobile: +27 79 69 77 082 >> 5 Jan Louw Str, Prince Albert, 6930 >> Postal: P.O. Box 2, Prince Albert 6930 >> South Africa >> http://www.zwartberg.com/ >> > > > > -- > Brian Modra Land line: +27 23 5411 462 > Mobile: +27 79 69 77 082 > 5 Jan Louw Str, Prince Albert, 6930 > Postal: P.O. Box 2, Prince Albert 6930 > South Africa > http://www.zwartberg.com/ > _______________________________________________ > 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
