[Digikam-users] map view seems to use odd EXIF tags

[Jean-François Rabasse]

Hello all and Happy New Year, full of attractive images ;)

On Tue, 31 Dec 2013, Martin Gerner wrote:

> Hello Jean-François and Michael -
> 
> Thank you for your replies - I have a better understanding of how Digikam
> operates now, and what you say makes sense. Re-reading the metadata of the
> images don't seem to change anything unfortunately, so it probably only
> considers the XMP section. I'll raise a bug for this.
> 
> Jean-François, I'm guessing that the software you use for correlating .gpx
> tracks with images does write to the XMP fields? What software is it?

Well, I currently use a test version of a correlating program I'm writing.
(The major reason is that I'm a bit unhappy with existing programs. My GPS
log device is a MobileAction GT120, a small, light weight, low cost, and
handy device, but small device means small antenna and not that great signal
to noise ratio, giving some spurious positions from time to time. When the
device aquires a position, at 5 seconds interval, and that new position is 
200 meters from the previous one, either you are a olympic level runner,
or the point is stupid.
Usual correlators can filter and discard points based on a minimal number
of satellites, but no one I know can discard on a velocity criterion.
And that's what I plan to do...)

But apart from that I've also being using exiftool for a long time, and 
still use it.

And you guess right, my GPS data is XMP data.
This, for philosophical reasons : many users - including me - consider that
Exif data is technical data written into the image file by a camera, and
should be considered as locked read-only data forever.
XMP schemas provide all the necessary editable informations and I personaly 
don't know any usecase where original Exif data should be modified.
Of course, it's nothing but an opinion.

So, I usually create XMP sidecar files from my original images, e.g. :
   exiftool -tagsfromfile XXX.JPG XXX.JPG.xmp

then do GPS correlation directly on the XMP files :
   exiftool -geotag tracklog.gpx XXX.JPG.xmp
with possible -geosync adjustements.

or, in a whole folder :
   exiftool -geotag tracklog.gpx *.xmp

That way, I never modify my original image file and original Exif section.
All metadata edition, title, rating, tags, description, copyright, et al.
is done at XMP sidecar file level.

This is the way I work, but I think same processing can be achived with
Digikam, from the moment your metadata setup is « Write to sidecar files
only ». Digikam can also create XMP sidecar files (using the libexiv2,
a little less complete than files produced by exiftool).


Regards,
Jean-François