[OSM-dev] Proposal: Database accelerator and dirty tile marker based on simple algorithm.

Anselm Hook anselm at hook.org
Wed Sep 20 17:32:35 BST 2006


Reading through the 44 messages in ths thread - I'm wondering if making a
conscious choice to take some time to research and try the shelf solutions
for this stuff - regardless of efficiencies or inefficiencies - wouldn't
be best?  The core value of OSM is data collection and advocacy - the rest
is just housekeeping; even if done badly it could be 'good enough'.

If you look at the discussion: Nick proposing a dirty tile marking
scheme, Nigel Magnay noting that tiles are only marked dirty at the
end-points of a line-segment (rather than more correctly dirtying a
bresenhams or a boundary of the line-segment) and proposing a quadtree.
Then the discussion moving onto using decimal integer coefficients (I
personally used hexadecimal coefficients for performance in
http://thingster.org/client.html which is an adobe svg only demo with
precomputed tiles)...  Overall you see a lot of possible branching
decisions that take significant mental computation to evaluate.

I do agree with Lars, although not the tone used, that PostGIS, GRASS and
the like should be leveraged.  The OpenLayers and the OSGEO community I
think would be more than happy to help standardize the back end data
representation and storage of line segments in such a way that all of the
concerns could be satisfied; such as making sure that tiles are never
obsolete.  The 'Mapping Hacks' book is worth spending a few days browsing
over; and it is worth even just trying mapserver, playing with postgresql,
ka-maps and the like such as OpenLayers is pushing.  There is even still
possibly a role for squid where it could be used as a tile invalidation
scheme.  For me, putting together http://maps.civicactions.net was pretty
trivial aside from the javascript mostly because I just used off the shelf
solutions.  I feel like there is so much value in what OSM is doing that
if there were some way that the strengths of GIS approaches could be used
without having to discard them due to gating considerations such as
concern over tile invalidation, that it would be best.

So no technical advice; just basically a 10,000 foot view comment...

 - a







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