[mapserver-users] calculating extent on basis of distance from point

[User Map]

hi,
i have OSGB36 data in postgre, srid 27700. what i want to do is to calculate the extent on basis of the distance from a given point. i have geom of type geometry in the table, from which to calculate extent. i have tried the funtions Distance(geom,geom)<50, but it is too slow, as it uses no index. i have calculated the point from the polygon by function Centroid(geom), from where the other distances have to be calculated, but i think its not working properly, as i am also testing it with the mapserver map and map saclebar, they are not matching exactly. i mean the scalebar is not showing 100 meter but instead showing 192 meters.
the main isuue is of the time the distance query is taking.
is there any why else to do this quickly.
thanks


      
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