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

[Ari Jolma]

Mateusz Loskot kirjoitti:
> Personally, I'm not sure if a data access layer is the right place to do
> such optimization, quite rendering-specific.
>   

Yes, rendering specific, but rendering, or geovisualization or mapping, 
is a (or the) major application area for geodata. Also, to be efficient, 
such optimization would probably need to be implemented near to the 
actual data access procedure.

This is the biggest headache I have in my geospatial GUI, I think. Has 
anybody seen rendering big vector data sets been satisfactorily solved 
in any desktop GIS? Often implementers show the incremental rendering so 
that users don't get bored while waiting, but it still is slow.

> I agree it would be worth to include this kind of functionality to the
> OGR geometry model, but as an option.
>   

A natural place for it would be a method, for example 
OGRLayer::SetSpatialApproximationFilter that would be similar as the 
method OGRLayer::SetSpatialFilter, i.e., it would be used in 
ResetReading, GetNextFeature loop. I haven't thought much about what 
kind of class a SpatialApproximationFilter would be, though.

Hm, this could be a very nice project for a student...

> 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?
>   

I think, rewrite the algorithm into OGR :)

Cheers,

Ari

-- 
Prof. Ari Jolma
Geoinformaatio- ja paikannustekniikka
Geoinformation and positioning technology
Teknillinen Korkeakoulu / Helsinki University of Technology
POBox 1200, 02015 TKK, Finland
Email: ari.jolma at tkk.fi URL: http://www.tkk.fi/~jolma