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

[Ari Jolma]

Mateusz Loskot kirjoitti:
>> Has anybody seen rendering big vector data sets been satisfactorily
>> solved in any desktop GIS?
> 
> It is a complex task, indeed.
> I've seen two approaches and the very base idea is not directly
> related to rendering, but to data management:
> 
> 1. load the whole geometry data into memory, into simple structures
> (arrays) - this is similar to how Manifold works

This is doomed to lead into problems once you try to open a theme with 5
million polygons...

> 
> 2. suck data from the disk (datasource like file/database) on every read
> (draw) - this is memory efficient but limited by speed of data medium
> access. This approach is used by GDAL, as well as old ArcView 3.x.
> 
> BTW, have you tried to implement simplifications out of OGR?

I'm currently using this approach. The code is in libral. It in fact
gets the data from OGR and converts it into another structure before
rendering (laziness on my part, it was easier that way to implement the
polygon rendering). I have not profiled the code extensively, it could
indeed be worth while to put a simplification algorithm just on top of OGR.

> 
>> Often implementers show the incremental rendering so that users don't
>> get bored while waiting, but it still is slow.
> 
> Yes, that's another possible improvement, also multi-threaded rendering

That would be a good idea, but I'm not that familiar with
multi-threading and AFAIK OGR might not support multi-threading?

Cheers,

-- 
Prof. Ari Jolma
Geoinformaatio- ja paikannustekniikka / Geoinformation and positioning
Teknillinen Korkeakoulu / Helsinki University of Technology
tel: +358 9 451 3886 address: POBox 1200, 02015 TKK, Finland
Email: ari.jolma at tkk.fi URL: http://www.tkk.fi/~jolma