[postgis-devel] ST_GeometrySplit

[Chris Hodgson]

It would be nice if the results were separated into "left" and "right". 
So you might return a geometrycollection which always contains 2 
components, the first one always being the left side and the second 
being the right. The geometries in the collection would have the 
appropriate type, perhaps minimized to the "lowest" applicable type 
(line vs. multiline or poly vs. multipoly).

I guess this result format is what would differentiate "split" from 
"difference", as with st_difference the results are effectively unioned 
into the most combined, minimal geometry, while with split you really 
want to keep things separate.

Right-side vs left side can be ambiguous too... an example is a circle 
or spiral that is split by a line on only one side. Perhaps a 3rd 
component to the resulting collection?

Chris

strk wrote:
> On Wed, Mar 10, 2010 at 08:51:18AM -0300, George Silva wrote:
>   
>> Hello guys,
>>
>> AFAIK, ArcGIS only handles the first case. One geometry splitting another,
>> even in multiple pieces, in case of the aforementioned C shape linestring.
>>
>> We should return multiple parts, as many as necessary: example, imagine
>> multiple "C" shape linestrings concatenated together:
>>
>> ___a________start
>> |__ b___
>> ___c___|
>> |__ d___end
>>      e
>>
>> In this case we would have 5 parts (I'm not sure if you all can see it...).
>>
>> Although the splitter line can be as complex as the user wants, it's a
>> single line.
>>     
>
> What kind of multi-part does ArcGIS returns ?
> A multiline in the "split line by line" seems good to me,
> but a multipoly in the "split poly by line" will be invalid
> as components would be "touching" on the split line.
>
> --strk;
>
>   ()   Free GIS & Flash consultant/developer
>   /\   http://strk.keybit.net/services.html
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