[postgis-users] More information on the new curve type

[Marshall, Steve]

You could add a text parameter called "interpolation_method" to the
curve interpolation functions.  If not specified, it would default to
the method you want to implement first (circular).  The implementation
of the SQL interpolation function would be to check the interpolation
type, then call the appropriate real interpolation function.  An error
would be thrown if an unsupported interpolation method was specified.

You could define an internal API underneath the SQL function, so that
other PostGIS users could add additional real interpolation functions
underneath.  

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paul
Ramsey
Sent: Monday, January 22, 2007 11:29 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] More information on the new curve type

Right now, because we don't do any operations on the curves, just
indexing and input/output, they can be said to "support" any
interpolation type you want... all we store are three control points for
each curve segment, you can interpret what happens between them how you
like.

However, once we start implementing operations, you'll find that the
interpolation type is circular arc, as specified by ISO.  That doesn't
stop you from using the storage/input/output routines and they doing any
operations outside the database in a tool that understands your
interpolation type.

Once you say "curve" everyone starts leaping up and down, asking about
their favourite interpolation type (Spline! No, clothoid! No, circle! No
bezier!), and I am not sure how to satisfy that demand without embarking
on a 10 year development project.  Anyone have any ideas?

Paul

Andreas Neumann wrote:
> Hello,
> 
> I am interested in the new curve type. Is there any information 
> (either by ISO/Opengeospatial or Refractions) available with some
examples?
> 
> Specifically, what geometry does the "curve" type support? Does it 
> support spline curves (if yes, which ones) or arc segments? I 
> understand that curve is sort of a superclass of Linestring, etc., but

> does it also support more complex curves like splines/beziers?
> 
> Thanks for any information,
> Andreas
> 


-- 

   Paul Ramsey
   Refractions Research
   http://www.refractions.net
   pramsey at refractions.net
   Phone: 250-383-3022
   Cell: 250-885-0632
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