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

[Jean-François Rabasse]

Hi Martin,

Some comments, as I geotag images files from GPX tracks logs too,
using an external program.

On Tue, 31 Dec 2013, Martin Gerner wrote:

> I used a piece of software to synchronize .gpx files with .jpg photos,
> with the effect of setting a number of GPS exif tags such as GPSLatitude, 
> GPSLongitude, etc (GPSversionID is 2.3.0.0). My understanding is that 
> geolocation tags can also be saved to "XMP Exif" tags - these tags were
> empty after synchronization.

Yes, Exif properties « can be saved » into proper XMP Exif schema, but this
isn't a law. It's up to the writing software to choose to update data in
the Exif section, or the XMP section, or both.
If your GPS correlation software updates only the Exif section, your
XMP data remain empty, or worse, can contain values from a previous GPS
correlation done with a different software.

Digikam keeps images GPS position in its database. These values will be
read when scanning for new images and reading their metadata, and will be
updated when you edit positions, inside Digikam.

> My suspicion at the moment is that the geolocation window reads location 
> data from the 'plain' EXIF fields (and probably the XMP ones too), that
> inconsistently the rest of the map views only read the XMP fields, and 
> that the reading of only the XMP fields is incorrect as it doesn't seem
> to match what other similar software does. It's a pain, since it means 
> that Digikam doesn't operate well together with other software.

No, Digikam functions don't read position data from Exif, or XMP, but
from the Digikam database. So they use what has been loaded when reading
images metadata.

But, when you write metadata to your images, or sidecar files, database
values are also exported into the Exif XMP schema.

And that's why, when you edit internally, database values are updated
then metadata is exported viw XMP schema :

> If I change the location of the photos in the geolocation window and apply
> the changes (from within Digikam), I can see that the XMP EXIF geolocation
> fields are updated for the photos; after this, they show up fine in the 
> rest of the map views in Digikam.
(Show up fine because the database has been updated, not because the data
has been XMP exported.)


I agree with Michael saying :

On Tue, 31 Dec 2013, Michael G. Hansen wrote:

> since you used external software to update the EXIF data, it may be that
> the database of digikam was not updated yet. You can select your newly 
> tagged photos and do Image->"Reread metadata from images".

You should check. If you first geocorrelate your images then start Digikam
and get the images as new images, metadata will be read.
But if you geocorrelate images already managed in Digikam, you have to
trigger « Reread metadata » so that Digikam updates its database.


As for compatibility with other software, my personal opinion is that
consistency must be guaranteed. GPS positions should be edited with one
and only one software, not different ones. This could ensure Exif GPS
data, or XMP GPS data be the same.

Most software will be able to read data in a fixed order, Exif data first
then XMP data. But I have no idea of what could they do, facing an 
inconsistency. Could probably lead to weird results.

As for me, I never faced that kind of problem because I edit positions
with an external program and writes only XMP Exif GPS data. So, the
original Exif GPS data in my images are always empty.
And I use Digikam only to « see » positions, not to edit.
(Of course, rereading metadata is required when I update positions from
outside.)

Regards, and Happy New Year :)
Jean-François