[postgis-devel] ST_GeometrySplit

[George Silva]

ArcGIS does not return a multipart geometry, but brand new records.

In the case showed, ArcGIS would return 4 new records, copying the old
values to the new ones.

George

On Wed, Mar 10, 2010 at 4:49 PM, Chris Hodgson <chodgson at refractions.net>wrote:

> 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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>>
>
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-- 
George R. C. Silva

Desenvolvimento em GIS
http://blog.geoprocessamento.net
(34) 9664-3717
(34) 8843-3717
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