[OSM-talk] What to display on the slippy maps - another approach

[John McKerrell]

On 16 Feb 2007, at 11:47, David Earl wrote:

> In discussing what osmarender should or shouldn't display, there's a
> continual compromise between a desire for the detail and cluttering  
> the map.
> The tiles are pre-rendered for efficiency in the slippy map. But  
> most of
> this is to do with lines and areas.
>
> But how about this: have the tiles rendered with all areas (*all*  
> areas) and
> lines (highways etc.) as thought fit, and selective nodes (e.g.  
> places). But
> leave all the other nodes off.
>
> Then on the slippy map, add the node icons and names dynamically on  
> top.
> Placing some tiny and cached transparent background prerenderd gifs 
> (*) for
> the icons will be much more efficient than a complete dynamic  
> rendering of
> an area. Placing icons can also be done lazily so that if someone  
> moves the
> map, we can cancel the overlaying for tiles which go off the area.
>

I'm very interested in doing something like this. I've actually been  
playing around with it but haven't got much further than a very  
simplified planet -> SQL script for pulling out interesting nodes.

>
> The overlaid nodes could be generated live from the database, but more
> likely could sit cached alongside the tile cache perhaps referenced  
> relative
> to their containing tile rather than by lat/long for efficient  
> display.
>
I'd probably go with a database, but indexed with a morton index to  
make it peedy.
>
> (*) they'd have to be gifs not pngs for now unfortunately because IE6
> doesn't render the transparency in pngs. IE7 does, but it will be a  
> long
> time before this is widespread enough.

PNGs can be made to work in IE6. I imagine we would use the openlayer  
API to overlay the POIs and that probably supports them automatically.

If I get any results from my playing around I'll post them on here.

John