[postgis-users] circular arcs in postgis?

[Hubert Fröhlich]

Hi Paul,
> That depends on what the meaning of "handle" is, and "rudimentary". :)
> The classic "solution" to dealing with arcs and whatnot in a simple  
> features environment is to convert them to simple features at load  
> time.  So the arc gets replaced with an interpolated line that closely  
> approximates its shape.  How does that sound?

I already have a similar approach: saving the "polygon" with arcs and 
straight lines mixed in a self defined format ( actually as "text") and 
extracting an approximated multipolygon ,with help of a function. The 
multipolygon can be extracted "on-the-fly" when needed, or can be 
written to a column of its own e.g. by a trigger when a new record is 
inserted

However, this results either in reduced performance especially when 
dealing with large datasets (several million polygons) and/or, in the 
latter case, with the need of storing the same information twice.

Can you imagine a more comfortable approach?

Greetings,
Hubert
> P.
> 
> On 28-Oct-04, at 9:29 AM, Hubert Fröhlich wrote:
> 
>> I am using postgis for storing and processing land register data.
>>
>> However, unfortunately, in our data model, the real estate plots are  
>> some kind of "multipolygon", however not in the "OGC Simple Feature  
>> for  SQL" sense - which restricts borders to straight lines
>>
>> ( in GML:
>> <gml:LineStringSegment>
>> <gml:pos> 4547584.06 5317944.32 </gml:pos>
>> <gml:pos> 4547590.66 5317944.07 </gml:pos>
>> </gml:LineStringSegment>
>> )
>>
>> , but also with cicrular arcs allowed as borders:
>>
>> e.g. in GML
>>
>> <gml:Arc interpolation="circularArc3Points">
>> <gml:pos> 4547582.29 5317942.87 </gml:pos>
>> <gml:pos> 4547582.92 5317943.89 </gml:pos>
>> <gml:pos> 4547584.06 5317944.32 </gml:pos>
>> </gml:Arc>
>>
>> I know this is a rather complicated issue - and I can't avoid it  
>> because the "data model" is from the good old days of analog mapping,  
>> measuring and calculating ,
>> I know that things (calculations) might turn really VERY complicated,  
>> but - is there a chance to extend Postgis data handling so such data  
>> types, maybe only in a rudimentary way?
>>
>> Greetings,
>>
>> Hubert
>> --  
>> ----------------------------------------------------------------------- 
>> --------
>> Dr.-Ing. Hubert Fröhlich           
>> Bezirksfinanzdirektion München            
>> Alexandrastr. 3, D-80538 München, GERMANY
>> Tel. :+49 (0)89 / 2190 - 2980
>> Fax  :+49 (0)89 / 2190 - 2997
>> hubert dot froehlich at bvv dot bayern dot de
>>
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> 
> 
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-- 
-------------------------------------------------------------------------------
Dr.-Ing. Hubert Fröhlich			
Bezirksfinanzdirektion München 			
Alexandrastr. 3, D-80538 München, GERMANY
Tel. :+49 (0)89 / 2190 - 2980
Fax  :+49 (0)89 / 2190 - 2997
hubert dot froehlich at bvv dot bayern dot de