[postgis-devel] ST_3DIntersection sometimes outputs TINs

[Paragon Corporation]

Olivier and Vincent,

I see that ST_3DIntersection sometimes outputs TINS even when none of the
inputs are TINS.  Whats the logic it uses to decide when to use the TIN
representation and the polyhedral representation?

Example:

SELECT ST_AsText(ST_3DIntersection(
		ST_GeomFromText('POLYHEDRALSURFACE Z( ((0 0 0, 0 0 1, 0 1 1,
0 1 0, 0 0 0)), 
		((0 0 0, 0 1 0, 1 1 0, 1 0 0, 0 0 0)), ((0 0 0, 1 0 0, 1 0
1, 0 0 1, 0 0 0)), 
		((1 1 0, 1 1 1, 1 0 1, 1 0 0, 1 1 0)), 
		((0 1 0, 0 1 1, 1 1 1, 1 1 0, 0 1 0)), ((0 0 1, 1 0 1, 1 1
1, 0 1 1, 0 0 1)) )'), 
		'POLYGON Z ((0 0 0, 0 0 0.5, 0 0.5 0.5, 0 0.5 0, 0 0
0))'::geometry))



Outputs:

TIN Z (((0 0 0,0 0 0.5,0 0.5 0.5,0 0 0)),((0 0.5 0,0 0 0,0 0.5 0.5,0 0.5
0)))


Thanks,
Regina