[postgis-users] Topological Exceptions

[Kevin Neufeld]

Martin Davis wrote:
> A reasonable concern.
>
> To which some might be tempted to reply RTFM.  (I think this is the 
> solution offered by some proprietary vendors...)
>
> Would having parallel sets of functions, (Paranoid/Laissez-faire) be 
> an option?  Unpleasant to widen the API, however.
>
We could override the methods to take an addition parameter, 
'ignore_exceptions boolean'.

In which case, we would have:
ST_Contains(geom,geom,boolean) => true, false, or null (if set to true)
ST_Contains(geom,geom)
  a simple wrapper for ST_Contains(geom,geom,false)

This way, people's queries won't break or wonder why the change in their 
outcomes.  If they want the "null" behaviour, they can ask for it.

-- Kevin
>> On 3/12/08, Paul Ramsey <pramsey at cleverelephant.ca> wrote:
>>> ...
>>>
>>>  This means that the return values of
>>>
>>>  ST_Contains(geom,geom) => true, false or null
>>>
>>>  and
>>>
>>>  ST_Intersection(geom,geom) => geometry or null
>>>
>>>  I just checked, and null seems to be interpreted as false in a WHERE
>>>  clause, so adding this behavior probably wouldn't wreck too many
>>>  joins.
>>>
>>>
>>>  Paul