[Openstreetmap] Re: Best time of day for urban canyon performance

[SteveC]

* @ 29/03/05 04:49:01 AM schuyler at nocat.net wrote:
> > My conclusion is that it isn't worth looking at unless you take in to
> > account all sorts of error sources and really have difficulty with some
> > spot getting reception, and don't want to average data.
> 
> What isn't worth looking at?

Ok, so I was thinking that if you knew there would be say a 30-60 minute
window of extra good reception then it might be worth using your gps at
that time in built up areas. Where 'extra good reception' means
satellites directly overhead, so they arn't blocked by buildings.

But, if you need a 60 degree cone up to get the minimum then its
difficult because modestly built up areas I was wandering around don't
even have that. So the most simple case of a cone doesn't seem super
useful.

The corollary to that is 

* You want good *vertical* accuracy. Hmmm.. .would need to turn sat
position in to some measure of DOP for each dimension.

* Instead of looking at a cone, assume you're in the middle of an
infinite street that runs in a straight line and do the visibility
analysis for that.

The other case is that you just assume a satellites will be visible down
the street and you want one or two above, but even for a 40 degree cone
this happens all the time (that you have 1 or 2 above) so a proper
analysis dones't seem useful. Eg, you don't mind tracking off of two
instead of threee minimum.

have fun,

SteveC steve at fractalus.com http://www.fractalus.com/steve/