cubicweb-postgis #3390052 Distance and point [validation pending]

We should bind some distance functions of postgis (ST_DISTANCE, ST_DISTANCE_SPHERE), and also bind a function to allow creation of point in RQL for distance computation.

prioritynormal
typebug
done in0.2.0
load0.500
load left0.000
closed by#ad76e6d2d3e5 [site cubicweb] Add more postgis functions, closes #3390052
patch[site cubicweb] Add more postgis functions, closes #3390052 [applied]