Re: [Geopriv] [geopriv] #14: uncertainty specification

> I think that uncertainty should be speicified in meters, independent
> from the CRS, and the members of the WG that i have spoken to seem to
> agree.

I agree too.

With uncertainty expressed in degrees one has to understand whether that
means:

1. (lat+/-u', lon+/-u')

    i.e. the region bounded by (lat-u -> lat+u, lon-u -> lon+u). The
shape of
    and area of this region depends on where you are on the globe, and you
also
    get large problems with wrap-around at the poles.

  or

2. (lat, lon) +/- u'

    i.e. anywhere within the 3d-chord specified with center (lat, lon)
subtending
    u degrees. This is a circular region that has almost the same shape
and area
    everywhere (WGS84 ellipsoid notwithstanding).

It's slightly tricky - personally if someone said " (51'N, 1'W) +/- 1' "
I'd probably assume definition 1 above, and take that to mean "50 - 52 N,
2 - 0 W".

However IMHO definition 2 is more intuitive. It's also much more
consistent with specifying the uncertainty in meters.

Ray

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Received on Fri, 31 Jul 2009 12:00:55 +0200