G'day Li, I can't help with Q2, but
On 01/04/2010, at 12:28 , Chen, Li [Contractor] wrote: > Q1. > ST_Buffer(g1, range) is able to return a geometry within the range of g1. > > So, I define two point using lon/lat (SRID=4326) and range 10km. I want to > see whether they cross each other by using ST_Crosses(g1, g2). > However, I don’t know the unit of the range parameter in ST_Buffer(g1,range) > as it is not provide in the docs. So is it km or meters? The same unit as your Geometry - decimal degrees. Obviously due to the change in the value of this unit at differing latitudes, this is not useful, so a more sensible approach is either to transform your point into a projection using metres, and then use metres (off the top of my head it would look like : select st_buffer(st_transform(g1, appropriate_projection_epsg),10000); but you should check the docs) or use the geography type from postgis 1.5? but I haven't tried it yet? cheers Ben _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
