On 15 September 2011 17:18, Yamini Singh <[email protected]> wrote: > Hi All, > > I have two questions to ask: > > Q1: I have a table that has one geometry column and I want to calculate > distance (in Km) between two geometries which is in one column. I am using > select query as under, and wanted to know if this is the right way of doing > distance calculation between two points. Since, both the points are in one > table but in different rows so I am using select statement to pick the geom > from > each row. > > select st_distance_sphere((select the_geom from table_name where > place_name='PL1'), (select the_geom from table_name where > place_name='PL2'))/1000; > > Q2: I have a table that has columns distance, direction, place_name > and geometry (with SRID 4326) as under. > > _________________________________________________________ > > | Id | distance | direction | Place_name | geom | > -------------------------------------------------------- > | 1 | 42 km | E | PL1 | some geometry| > > --------------------------------------------------------- > > Now I want to calculate new geometry with reference to given geometry based > on some distance and direction. Such that new geometry is at ?42km E of some > reference geometry?. Is there a function that can do this? Or if someone can > point me to a specific link.. >
Hi Yamini, It may be easier to first reproject your data to a planar system before translating geometries, then st_translate() should do the trick. Based on distance and direction, you can compute the deltax and deltay translation parameters and give them to st_translate (here, 42 000 m (assuming your planar projection system is in meters) added to X coordinate will translate the input geometry east. I don't think st_translate will be able to work with geographic data without some maths to convert from KM to degrees, taking into account currrent latitude. Nicolas _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
