[postgis-users] voronoi fails on regular grid

[J.J. Green]

Hi Darafei,

Many thanks for your reply

> Please post your points to https://trac.osgeo.org/geos/ as a bug report.

I'll do that

> In my experience two things help with Voronoi issues:
>   - ST_SnapToGrid;
>   - falling back to non-geos voronoi implementation, 

In fact the first of those works beautifully -- I tried several
values and found that dyadic fractions (as in 1/2^n) work best,
this kind-of makes sense since it "zeros-out" the bottom-end of
the floats, and then calculations with them should be exact
(provided the input numbers are of the same order, and they are).

For the sake of others happening across this issue, my
working Voronoi call is now

   CREATE TEMPORARY TABLE cell_poly_tmp ON COMMIT DROP AS
     SELECT
       Geometry(
         (
           ST_Dump(
             ST_CollectionExtract(
               ST_VoronoiPolygons(
                 ST_SnapToGrid(
                   ST_Collect(point),
                   pow(2.0, -8)
                 ),
                 0.0
               ),
               3
             )
           )
         ).geom
       ) AS poly
     FROM cell_point_tmp;

Thanks again!

Jim
-- 
J.J. Green
http://soliton.vm.bytemark.co.uk/pub/jjg/en/