[Openstreetmap] landsat background to the static renderer
Lars Aronsson
lars at aronsson.se
Sat Jul 16 19:19:31 BST 2005
Tom Carden wrote:
> There's a limit of 5000 nodes on the static renderer to stop the
> server from falling over. Until we have a way to distinguish
> "main roads" from others, or to cache the images, it's likely
> that looking at a whole continent will be less than
> satisfactory.
It is good that we have this problem, because it means we have a
lot of data. Growing pain means we are growing. A working
solution must be based on our continued growth.
Every street segment has a visible size. On a map-of-Europe where
scale=0.1 every pixel is 0.1 degrees or 11 km. All points within
a small city becomes a single pixel. Instead of looking at the
maybe 400 points that make up the street net of that city, we
could look at generating one pixel: should it be white or not?
Each entire map is 700x500 = 350,000 pixels. This is constant and
doesn't change with the map scale or amount of data we collect.
All we need is a fast way to query the database: Is there anything
within this 11x11 km area? If this can be answered in 1
microsecond, then 350,000 such queries can be answered in 0.35
seconds, which would be a reasonable response time for a
webserver. I guess this is a standard GIS problem. Quad trees?
--
Lars Aronsson (lars at aronsson.se)
Aronsson Datateknik - http://aronsson.se
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