[Imports-us] [Talk-us] Rail westerly

Darrell Fuhriman darrell at garnix.org
Wed Dec 31 22:09:58 UTC 2014


Yes, WGS84 because that’s what’s used by GPS (which was, after all, the original data source for OSM). 

Of course, then there’s the question of *which* WGS84 definition we’re talking about. You actually can’t assumed that current definitions of WGS84 and NAD83 are <1m difference.  You can dip your toe into the complexity here: http://www.ngs.noaa.gov/CORS/Articles/WGS84NAD83.pdf

Also note, that the satellite photography used for a great deal of OSM mapping has much less than 1m accuracy, and as you note, unless you’re using expensive GPS, you’re not likely to get <1m accuracy anyway.

Relatedly, I’m curious if anyone has used one of these guys: http://gps.dualav.com/explore-by-lifestyle/outdoors/

d.

On Dec 31, 2014, at 13:56, Dave Mansfield <mansfieldd at chartermi.net> wrote:

> 
> That brings up a good question. What datum is used by OSM? I would assume it's WGS 84. NAD 83 is within about a meter of WGS 84. That’s closer than the GPS units most of us have so would not cause much of an error if any. NAD 27 on the other hand could be off by as much as 180 meters.
> 
> Dave
> 
> -----Original Message-----
> From: stevea [mailto:steveaOSM at softworkers.com] 
> Sent: Wednesday, December 31, 2014 2:24 PM
> To: talk-us at openstreetmap.org
> Cc: imports-us at openstreetmap.org
> Subject: Re: [Talk-us] Rail westerly
> 
> I examine these in JOSM right now.  First they need to be unzipped, and it looks like the (provided on that web page) PRJ file to change from WGS 84 (default) to either NAD 27 or 83 projection is required. 
> I haven't done that to these data in the instant case, but I've fiddled these before and I think it is doable.
> 
> SteveA
> California
> 
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