[OSM-dev] Cartagen - client-side vector based map renderer, dynamic maps

Stefan de Konink stefan at konink.de
Thu May 7 20:24:12 BST 2009


Jeffrey Warren wrote:
> Wow, this is fantastic and very exciting! Stefan - by javascriptsockets 
> were you thinking of the thru-flash technique for sockets? 

I have two options; I was indeed looking at the flash technique for 
native protocol access. Alternatively the Cherokee Webserver has its own 
'dbslayer' implementation this allows an SQL database to be queried over
HTTP and outputed in the common formats [json/xml/cvs/...]

> I'd love to 
> help out if I can. Right now, Cartagen doesn't use sockets, but small 
> Ajax requests every 1/3 of a second. Latency is low but not quite 
> realtime... it's within about a second but depends on the size of the 
> plot requested of course. I've been avoiding Flash because it's not 
> available on the iPhone or Android, and it'd be nice to have almost the 
> same renderer/editor codebase on mobile devices and PC.

I don't want to reinvent the wheel, so I will checkout how you build 
this thing and probably hook in some code.

> Just curious, how does Mapnik or Omsarender do it? Surely they don't 
> actually render every node of a way for very large bboxes?

In the default Mapnik case polylines are fetched, so that is basically 
an operation that already has a materialized linestring. Since the 
tables know what type the line will be it is just a draw this line at 
that point. [A bit more complex due to layer = ...]


Stefan




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