[Digikam-devel] GPS wrong coordinate conversion?

[Arnd Baecker]

Hi,

maybe I am wrong, but I think that the conversion in the example
given at
http://docs.kde.org/development/en/extragear-graphics/digikam/using-kapp-camera.html#using-kapp-gps
is not correct:

"""The positional data (e.g. 13.44088333) must be converted into H.MS
format (13.235990) and split into its constituents as shown in the given
example."""

which leads to the entry
  add Exif.GPSInfo.GPSLatitude Rational "13/1 23/1 5990/100"

Doesn't 13.44088333 convert to: 13 26 27.18:
  int(13.44088333)       = 13
  int(0.44088333*60)     = 26
  (0.44088333*60-26) *60 = 27.18

The converter at http://www2.comp.polyu.edu.hk/~04329143d/Location.html
also gives these numbers.
If this is correct, it should read
  add Exif.GPSInfo.GPSLatitude Rational "13/1 26/1 2718/100"

The other way round, "13/1 23/1 5990/100"
would correspond to: 13.399972.

Best, Arnd
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[Gilles Caulier-2]

Le Vendredi 08 Septembre 2006 05:43 PM, Arnd Baecker a écrit :

> Hi,
>
> maybe I am wrong, but I think that the conversion in the example
> given at
> http://docs.kde.org/development/en/extragear-graphics/digikam/using-kapp-ca
>mera.html#using-kapp-gps is not correct:
>
> """The positional data (e.g. 13.44088333) must be converted into H.MS
> format (13.235990) and split into its constituents as shown in the given
> example."""
>
> which leads to the entry
>   add Exif.GPSInfo.GPSLatitude Rational "13/1 23/1 5990/100"
>
> Doesn't 13.44088333 convert to: 13 26 27.18:
>   int(13.44088333)       = 13
>   int(0.44088333*60)     = 26
>   (0.44088333*60-26) *60 = 27.18
>
> The converter at http://www2.comp.polyu.edu.hk/~04329143d/Location.html
> also gives these numbers.
> If this is correct, it should read
>   add Exif.GPSInfo.GPSLatitude Rational "13/1 26/1 2718/100"
>
> The other way round, "13/1 23/1 5990/100"
> would correspond to: 13.399972.
>
> Best, Arnd

Arnd,

The code relevant of GPS position decoding is in this source file :

http://websvn.kde.org/trunk/extragear/graphics/digikam/libs/widgets/metadata/gpswidget.cpp?rev=580664&view=auto

Look the method decodeGPSPosition() at end of file.

I'm busy this week end to check if something is wrong...

Gerhard, can you check this part please. Thanks in advance.

Gilles
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[Arnd Baecker]

Hi Gilles,

On Sat, 9 Sep 2006, Caulier Gilles wrote:

> Le Vendredi 08 Septembre 2006 05:43 PM, Arnd Baecker a écrit :
> > Hi,
> >
> > maybe I am wrong, but I think that the conversion in the example
> > given at
> > http://docs.kde.org/development/en/extragear-graphics/digikam/using-kapp-ca
> >mera.html#using-kapp-gps is not correct:
> >
> > """The positional data (e.g. 13.44088333) must be converted into H.MS
> > format (13.235990) and split into its constituents as shown in the given
> > example."""
> >
> > which leads to the entry
> >   add Exif.GPSInfo.GPSLatitude Rational "13/1 23/1 5990/100"
> >
> > Doesn't 13.44088333 convert to: 13 26 27.18:
> >   int(13.44088333)       = 13
> >   int(0.44088333*60)     = 26
> >   (0.44088333*60-26) *60 = 27.18
> >
> > The converter at http://www2.comp.polyu.edu.hk/~04329143d/Location.html
> > also gives these numbers.
> > If this is correct, it should read
> >   add Exif.GPSInfo.GPSLatitude Rational "13/1 26/1 2718/100"
> >
> > The other way round, "13/1 23/1 5990/100"
> > would correspond to: 13.399972.
> >
> > Best, Arnd
>
> Arnd,
>
> The code relevant of GPS position decoding is in this source file :
>
> http://websvn.kde.org/trunk/extragear/graphics/digikam/libs/widgets/metadata/gpswidget.cpp?rev=580664&view=auto
>
> Look the method decodeGPSPosition() at end of file.

I think that the code in the routine PSWidget::decodeGPSPosition
is alright.
It is just the example in the documentation which I cannot reproduce
(Maybe I am messing up things, as I don't have any experience
with GPS and all the coordinate stuff...).

> I'm busy this week end to check if something is wrong...

No problem - nothing urgent anyway ;-)

> Gerhard, can you check this part please. Thanks in advance.

I just checked the GPS plugin with two different places
(using exiv2 to add GPS info) and it seems to work fine
(of course I cannot check it precisely due to the lack of zooming
and also not to the accuracy of a few meters
because of the scale of the map - don't  get me wrong, no criticism
here, I know that further GPS stuff is post 0.9, and all this is a
great start!!)

Many thanks, Arnd

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[Gerhard Kulzer]

Am Samstag, 9. September 2006 11:19 schrieb Arnd Baecker:

> Hi Gilles,
>
> On Sat, 9 Sep 2006, Caulier Gilles wrote:
> > Le Vendredi 08 Septembre 2006 05:43 PM, Arnd Baecker a écrit :
> > > Hi,
> > >
> > > maybe I am wrong, but I think that the conversion in the example
> > > given at
> > > http://docs.kde.org/development/en/extragear-graphics/digikam/using-kap
> > >p-ca mera.html#using-kapp-gps is not correct:
> > >
> > > """The positional data (e.g. 13.44088333) must be converted into H.MS
> > > format (13.235990) and split into its constituents as shown in the
> > > given example."""
> > >
> > > which leads to the entry
> > >   add Exif.GPSInfo.GPSLatitude Rational "13/1 23/1 5990/100"
> > >
> > > Doesn't 13.44088333 convert to: 13 26 27.18:
> > >   int(13.44088333)       = 13
> > >   int(0.44088333*60)     = 26
> > >   (0.44088333*60-26) *60 = 27.18
> > >
> > > The converter at http://www2.comp.polyu.edu.hk/~04329143d/Location.html
> > > also gives these numbers.
> > > If this is correct, it should read
> > >   add Exif.GPSInfo.GPSLatitude Rational "13/1 26/1 2718/100"
> > >
> > > The other way round, "13/1 23/1 5990/100"
> > > would correspond to: 13.399972.
> > >
> > > Best, Arnd
> >
> > Arnd,
> >
> > The code relevant of GPS position decoding is in this source file :
> >
> > http://websvn.kde.org/trunk/extragear/graphics/digikam/libs/widgets/metad
> >ata/gpswidget.cpp?rev=580664&view=auto
> >
> > Look the method decodeGPSPosition() at end of file.
>
> I think that the code in the routine PSWidget::decodeGPSPosition
> is alright.
> It is just the example in the documentation which I cannot reproduce
> (Maybe I am messing up things, as I don't have any experience
> with GPS and all the coordinate stuff...).
>
> > I'm busy this week end to check if something is wrong...
>
> No problem - nothing urgent anyway ;-)
>
> > Gerhard, can you check this part please. Thanks in advance.
>
> I just checked the GPS plugin with two different places
> (using exiv2 to add GPS info) and it seems to work fine
> (of course I cannot check it precisely due to the lack of zooming
> and also not to the accuracy of a few meters
> because of the scale of the map - don't  get me wrong, no criticism
> here, I know that further GPS stuff is post 0.9, and all this is a
> great start!!)
>
> Many thanks, Arnd
>

Well there are no hard feeling here, rather the contrary. I'm still a bit
puzzled because I used a HP calculator (which is usually a rock-solid
reference) to make the conversion. It still gives me the same (wrong values).
I believe you are right.

By the way, I recently updated the maps.google interface to include a marker
at the spot of the location. When you zoom in you should be able to verify
your coordinates. I will do that too: take coordinates from maps.google,
convert them stick them into a picture and open maps.google from digikam.
They should match exactly.
Gerhard

--
http://www.gerhard.fr
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