On Tue, Jun 25, 2013 at 12:31:41PM +0200, Sandro Santilli wrote: > On Tue, Jun 25, 2013 at 11:48:03AM +0200, Egil Möller wrote: > > Hi! > > > > I'm implementing a dynamic clustering of points in a map, where if you > > zoom out, any area with too many points in it has its points replaced by > > a big circle with the number of points it's covering written on it. When > > you zoom in, the big circles are gradually replaced with several smaller > > circles and finally with individual points. > > > > On the server side this is implemented using ST_SnapToGrid followed by a > > group by (with count) over the table with the points. Then for each row > > where count < some number, a new select query is done to get the actual > > points in the area. > > > > The problem is that I seem to get the are to select points from wrong. > > So, here's the question: > > > > Given that > > > > ST_SnapToGrid(ST_Point(lon, lat), sizeLon, sizeLat) = > > ST_Point(resultLon, resultLat) > > > > for a given pair of values resultLon and resultLat, and given > > sizeLon and sizeLat, what are the min and max values for lon and lat? > > They should be : > > resultLong +/- sizeLon > resultLat +/- sizeLat
Sorry, that is: resultLong +/- (sizeLon/2) resultLat +/- (sizeLat/2) --strk; > > > This does not seem to be documented anywhere in > > http://postgis.net/docs/manual-2.0/ST_SnapToGrid.html :( > > Patch welcome (after confirmation:) > > --strk; _______________________________________________ postgis-users mailing list [email protected] http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
