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

[Martin Gerner]

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?

Thanks,
Martin

On 31/12/13 16:52, Jean-François Rabasse wrote:
>
> 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
>
>
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