[OSM-dev] Ways on the new renderer... maybe usable after all!

[Lars Aronsson]

David Sheldon wrote:

> On Fri, Jun 30, 2006 at 04:15:50PM +0200, Lars Aronsson wrote:
> > Adding more hardware is not going to solve this.  We'd have to 
> > wait ten years for Moore's law to have that effect.  So how are we 
> > going to solve it?
> 
> As far as I can tell, the only way to improve it is to change the
> datastructures in the database. Maybe denormalise a bit. 

How does traditional GIS software solve this, e.g. MapServer?  
Perhaps OSGEO could help here, if they're committed to improving 
software.

> The SQL at the moment requires many queries for a single tile. You will
> not get 40ms response times when you are calling that many queries.

But even if we could, retrieving every line segment in Greater 
London for the "map of England" scale doesn't make sense.  The 
amount of data we need to retrieve has to be reduced far more.

Every tile is 256 x 128 pixels = 32768 pixels.  On the map of 
England scale (zoom 6, or so) every pixel would cover hundreds of 
line segments.  There is little point in retrieving hundreds of 
line segments from the database only to determine whether that 
pixel should be pink indicating an urban area, dark red indicating 
a motorway or transparent representing the countryside.

> Removing the historical data from the tables will be a good 
> start (and we keep on comming back to this).

I agree that this would be a good idea anyway, but it's not a 
solution because the historic data is perhaps only 50% of the 
database.  And we need to remove 99% of our current time lag.


-- 
  Lars Aronsson (lars at aronsson.se)
  Aronsson Datateknik - http://aronsson.se