[postgis-devel] about lwcurve in postgis

Håvard Tveite havard.tveite at umb.no
Mon Jun 23 05:53:13 PDT 2008


According to my (not final version of) SQL-MM, ST_Curve is
not instantiable:

"ST_Geometry, ST_Curve, and ST_Surface are not instantiable
types. No constructor functions are defined for these types."

Håvard

xie jiong wrote:
> SQL-MM specification's curve is the base class of circluar string and line string,
> so use curve as circle isn't very proper i think.
> 
> ----- Original Message -----
> From: "Mark Leslie" <mrk.leslie at gmail.com>
> To: "PostGIS Development Discussion" <postgis-devel at postgis.refractions.net>
> Sent: Thursday, June 19, 2008 7:40 AM
> Subject: Re: [postgis-devel] about lwcurve in postgis
> 
> 
>> 2008/6/18 xie jiong <xie_jiong at 163.com>:
>>> HI:
>>>
>>> in current postgis, lwcurve only represent circularstring, so why use
>>> curve name?
>>>
>>> Jiong
>>> _______________________________________________
>>> postgis-devel mailing list
>>> postgis-devel at postgis.refractions.net
>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel
>>>
>>>
>> One answer is that a circle is a curve.
>>
>> The correct answer is that the curved geometry support was developed
>> to the SQL-MM specification, which supports only the circular string
>> version of curves, so our naming convension is directly derived from
>> theirs.
>>
>> --
>> Mark Leslie
>> Geospatial Software Architect
>> LISAsoft
>> http://www.lisasoft.com/LISAsoft/SupportedProducts.html
>> _______________________________________________
>> postgis-devel mailing list
>> postgis-devel at postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-devel

-- 
Håvard Tveite
Department of Mathematical Sciences and Technology, UMB
Drøbakveien 31, POBox 5003, N-1432 Ås, NORWAY
Phone: +47 64965483 Fax: +47 64965401 http://www.umb.no/imt/



More information about the postgis-devel mailing list