[Digikam-devel] GPS coordinate accuracy

[Andreas Huggel]

On Friday 24 November 2006 23:24, Gilles Caulier wrote:
> On Friday 24 November 2006 16:26, Arnd Baecker wrote:
[...]
> > - In the GPS Info Tab in the sidebar of digikam the
> >   location is given as 54'1.41''.
> >   Why not just use the decimal variant here as well?
>
> (:=))...
>
> I let's others digiKam users GPS fan talking about your remark.
>
> Julien, Fabien, Gerhard, ...
>
...count me in :)

I've tweaked the exiv2 logic a bit for the upcoming 0.12 release. Since 
the exiv2 output is shown in digikam if I'm not mistaken, here is what 
it is now:

Consider
   3.14159292 degrees, which can also be written as 
   3deg 8.4955752' or
   3deg 8' 29.734512"

Depending on how the value is encoded in the Exif data (*), exiv2 will 
show 7 decimal places for degrees, 5 for minutes and 3 for seconds, 
i.e.,
   3.1415929deg (**)
   3deg 8.49558'
   3deg 8' 29.735"

Converting this to distance, the corresponding accuracies of such values 
are (at least):
   10^-7deg ~ 1.1cm
   10^-5'   ~ 1.9cm
   10^-3"   ~ 3.8cm

i.e., all much lower than the best GPS accuracy you can ever get, so 
there shouldn't be a concern that the numbers shown do not correspond 
to a location determined by GPS accurately enough.

(*) In the Exif field, longitude and latitude values must be encoded as 
three rationals (two 32bit integers each): the number of degrees, 
minutes and seconds. Fractions are obviously possible for all three and 
one specific value can be encoded in multiple ways.

(**) I also replaced the degree sign with 'deg', due to charset 
concerns.

-ahu.