[OSM-newbies] Trust GPS or Yahoo aerial imagery?

[Gervase Markham]

Rick Collins wrote:
> So how does this mean that GPS signals are more accurate?  The last 
> time I checked, GPS calculations were done by explicitly calculating 
> both the position and the speed of multiple satellites in a very high 
> orbit, which means a very, very high speed compared to an aircraft or 
> low earth orbit.

Indeed. But this particular calculation _is_ in fact something that 
someone has spent billions of dollars on, if you will permit me to use 
your argument, as the US Government uses it to pass Tomahawks through 
windows.

I know we don't necessarily get their accuracy, but my point is that the 
original calculation is going to be very, very good.

>> My GPS on the other hand, is an OpenStreetMap recommended model, and I
>> was walking up and down the centre of the roads (not cycling or driving)
>> with a clear view of the sky.
> 
> I have no idea what is meant by "OpenStreetMap recommended 
> model".  Are you trying to say that your model of GPS receiver is 
> more accurate and consistent than others?  

No, I mean that the openstreetmap.org wiki recommends it on their 
hardware reviews page, and has even set up a special deal so they get 
some money when you buy one. It's a NaviGPS (BGT-11 model).

> How was that 
> determined?  What model is it?  How about checking your route by 
> comparing to some other data rather than just making an assumption 
> about which is more accurate and which is less accurate?  If you 
> don't want to use the USGS images, why not try measuring the same 
> route on multiple days?  

What are these USGS images you speak of? I haven't seen them as an 
option or an add-in for JOSM. Are they as high-res as the Yahoo images 
in the area in question?

Gerv