[Gdal-dev] Re: what about OGRCircle , OGRArc and OGREllipse

[Jacob Bensabat]

Hi and thanks for your message.
I understand now your point of view.
jac


"Frank Warmerdam" <warmerdam at pobox.com> wrote in message
news:40FFBECD.4000200 at pobox.com...
> Jacob Bensabat wrote:
> > hello to all
> > I have seen the need to draw arcs, ellipses and circles using ogr. The
> > problem is that these
> > geometric features are not directly supported by OGR. There seems to be
no
> > problem adding
> > them so my question is why these are not supported. Is there any reason
> > (conceptual or practical
> > one) ?
>
> Jacob,
>
> Basically, they aren't there because they aren't part of the simple
features
> geometry model, though they do have obvious (and intended) places to fit
as
> add-ons to that geometry model.  While I wouldn't necessarily mind having
> OGR classes for them, it is important to note that alot of stuff wouldn't
> work properly for them.  For instance, there would presumably be hardly
> any drivers that would support them.  Also, translation to WKT and WKB
would
> not be compatible with stuff like GEOS or PostGIS.
>
> Basically, my concern is that they wouldn't be well supported and that in
many
> cases it would be better to have just converted them into polyline or
polygon
> approximations.
>
> An important step in any system design is coming up with a data model.   I
> chose the OpenGIS Simple Features geometry model as a basis for OGR and it
> has provided me with a great deal of leverage in terms of compatibility
with
> other systems.
>
> Of course it does not lend itself to accurate or efficient representation
of
> some feature from CAD oriented systems.  However, that hasn't been a huge
issue
> for me till this point.
>
> In short, if you are interested I wouldn't necessarily mind having classes
for
> ellipse, circle and so on, but I would want to include big disclaimers on
them
> that they are not widely supported.  Furthermore, I would likely not want
to
> make drivers like DGN actually return these geometries even where it would
make
> sense as they would not be translatable to other drivers.
>
> Best regards,
> -- 
> ---------------------------------------+----------------------------------
----
> I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial Programmer for Rent