[postgis-devel] ST_GeometrySplit

[Chris Hodgson]

Works for the line case though:

select st_astext(st_difference( st_geomfromtext('LINESTRING(0 0, 0 2)'), 
st_geomfromtext('LINESTRING(-1 1, 1 1)')));
              st_astext              
--------------------------------------
 MULTILINESTRING((0 0,0 1),(0 1,0 2))

Perhaps the point case is a precision issue? Or I don't know the exact 
spec for this function.

Not the result I expect for the polygon-line case either:

select st_astext(st_difference( st_geomfromtext('POLYGON((0 0, 0 2, 2 0, 
0 0))'), st_geomfromtext('LINESTRING(-1 1, 2 1)')));
             st_astext             
------------------------------------
 POLYGON((0 0,0 1,0 2,1 1,2 0,0 0))

I'm running on old stuff here, maybe someone can check on a newer version...

select postgis_full_version();
                                
postgis_full_version                                
-------------------------------------------------------------------------------------
 POSTGIS="1.3.3" GEOS="3.0.0-CAPI-1.4.1" PROJ="Rel. 4.6.1, 21 August 
2008" USE_STATS

Chris


Chris Hodgson wrote:
> Hmm... nevermind, I guess it's not.
>
> select st_astext(st_difference( st_geomfromtext('LINESTRING(0 0, 0 
> 2)'), st_geomfromtext('POINT(0 1)')));
>      st_astext     ---------------------
> LINESTRING(0 0,0 2)
>
> Chris
>
> Chris Hodgson wrote:
>> Isn't this the same as st_difference(A,B), when given any of those 
>> pairs of arguments? Wrap it in an st_dump() if you want to separate 
>> the individual results?
>>
>> Chris
>>
>> strk wrote:
>>> Brain picking you guys about a ST_GeometrySplit.
>>>
>>> The cases of interest seem to be:
>>>  - Split polygon by line
>>>  - Split line by line
>>>  - Split line by point
>>>
>>> Initial questions:
>>>  - Should we allow multi-segment "blade" lines ?
>>>    (where a single polygon or line might be cut in multiple pieces)
>>>  - Should we allow multi-component inputs ?
>>>    (where the "blade" might cut a single component)
>>>
>>> Both questions are related to the kind of returned output,
>>> that is: should output be always composed by 2 parts or
>>> possibly multiple parts ?
>>>
>>> Comments welcome.
>>>
>>> --strk;
>>>
>>>   ()   Free GIS & Flash consultant/developer
>>>   /\   http://strk.keybit.net/services.html
>>> _______________________________________________
>>> postgis-devel mailing list
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>>>   
>>
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