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

[Andreas Neumann]

yes, I can certainly understand that adding various different curve 
algorithms creates a lot of complexity for the implementations. 
Suddenly, all the operators are more complex to implement, imagine doing 
buffers on spline curves, intersect, etc. Its certainly doable (Adobe 
Illustrator, CorelDraw, Inkscape, etc) - they do it, but it probably 
adds complexity to the Postgis/Geos code.

Then there is the question how curves would be transformable to other 
map projections? Would one just project the control points? Would 
probably lead to strange results, sometimes ...

Personally, I was hoping to find a match for the SVG supported curve 
types: quadratic and cubic bézier and arc segments. I do a lot of web 
mapping with SVG (see e.g. http://www.carto.net/williams/yosemite/ ), 
mostly based on Postgis as a backend, and having a match for quadratic 
and cubic béziers would be fantastic. Just dreaming ... Many 
cartographic datasets would benefit from spline support, e.g. river 
networks, roads and railway tracks, etc.

Andreas

Paul Ramsey wrote:

> 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
>


-- 
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Andreas Neumann
Institute of Cartography
ETH Zurich
Wolfgang-Paulistrasse 15
CH-8093  Zurich, Switzerland

Phone: ++41-44-633 3031, Fax: ++41-44-633 1153
e-mail: neumann at karto.baug.ethz.ch
www: http://www.carto.net/neumann/
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