[Gdal-dev] Rendering optimization [Re: Looking for huge vector dataset]

[Mateusz Loskot]

Ari Jolma wrote:
> Mateusz Loskot kirjoitti:
>> Hi,
>> 
>> I'm looking for a big set of vector data, ideally available as
>> public geodata. I mean big as including >= 100 000 number of
>> features with geometries, preferable of type of polygon or
>> linestring.
>> 
>> If anyone does have such data and could share with me, I'd be very 
>> thankful!
>> 
>> I'm going to use it *only* for testing and benchmarking GDAL/OGR, 
>> no other purpose (like commercial) is considered.
>> 
> 
> What I would be interested in having in OGR is a fast on-the-fly 
> overviewing. Right now it takes quite a lot of time to go through
> large datasets like this for rendering. The only optimization I have 
> implemented in my visual code on top of OGR is to first check if the 
> whole feature is smaller than one pixel in the current viewport and
> then avoid invoking line or polygon draw. I think there was some
> discussion a while back on implementing Douglas-Peucker, but is
> anybody doing that? Something like RaveGeo (idevio.com) would be
> cool.

Ari,

Personally, I'm not sure if a data access layer is the right place to do
such optimization, quite rendering-specific.
I agree it would be worth to include this kind of functionality to the
OGR geometry model, but as an option.

GEOS does offer Doublas-Peucker algorithm implementation, so may be we
could try to incorporate it into OGR similarly to other GEOS stuff,
optional.

The only potential problem I see is that transforming OGR geometry to
GEOS geometry is/might be quite expansive in most cases.

What do you think?

Cheers
-- 
Mateusz Loskot
http://mateusz.loskot.net