[Xastir] Announcing tile support for OSM

[Jeremy McDermond]

On Jul 27, 2010, at 4:53 PM, Curt, WE7U wrote:

> On Wed, 28 Jul 2010, James Cameron wrote:
> 
>> Are the http requests streamed in one connection, or are there multiple
>> connections?  Are the multiple connections fired simultaneously or are
>> they queued one by one?
>> 
>> The reason I ask is that several users are on high latency connections,
>> such as satellite or commercial wireless "broadband", and a tiling
>> implementation that makes multiple requests pays the latency penalty
>> many times.
> 
> The requests are lined up serially, plus you can interrupt between
> them with a pan or zoom or F4.  F4 gives you the optimum zoom level
> in Xastir to match the tile resolution that's nearest.  I believe
> Jerry mentioned that the OSM servers will only accept 2 connections
> at a time from one address anyway, so you can't do much in the way
> of parallel operation to begin with.

I don't think the real question is whether they're simultaneous, but whether the HTTP request can be pipelined.  That way you can request multiple tiles in one TCP connection and save the TCP setup costs over a high latency connection.

> 
> In any case, once you have an initial set of tiles to match your
> desktop, panning only requests a few tiles along the new edge.  For
> zooming you take a hit, but only the first time.  It gets faster as
> it "learns" the area you move around in (because of caching the
> tiles).
> 
> -- 
> Curt, WE7U.                         <http://www.eskimo.com/~archer>
>   APRS:  Where it's at!                    <http://www.xastir.org>
>  Lotto:  A tax on people who are bad at math. - unknown
> Windows:  Microsoft's tax on computer illiterates. - WE7U.
> The world DOES revolve around me:  I picked the coordinate system!"

--
Jeremy McDermond (NH6Z)
Xenotropic Systems
mcdermj at xenotropic.com