Composite Location Tags

[Gennaro]

Hi all,

after a bit of searching on internet and forums, there's something that it is still not entirely clear.

As far as I seem to understand, the values of the "Composite" tags are derived from the values of other tags - I found many of these and how they are derived on the ExifTool website and elsewhere.

This brings to my first question:

(1) How is it possible that some composite tags can be directly modified and are not locked?


As regarding the location tags, I do not entirely understand how they work. If I add country/state/city/location (either through reverse geocoding or through the location metadata subpanel), all of these metadata are part of the "Composite" tags, except ISO Country Code which is written directly into the relevant IPTC Core field.

When Metadata are written back into the (jpg) file, their values propagate to the relevant IPTC metadata (Location Shown City, etc.), according to IMatch default rules.

(2) I do not understand why all these location metadata are in "Composite" tags and not written directly as XMP IPTC tags.

Furthermore, if they did not propagate, where would they be stored? Are they user-defined Exif Composite tags which can be recognized by any (modern) software?


thanks a lot,
Gennaro

[Mario]

(1) How is it possible that some composite tags can be directly modified and are not locked?

IMatch displays all tags as writable which are reported by ExifTool as writable.
A number of the Composite tags is writable and when the data for these tags is updated in IMatch, ExifTool works it's magic at write-back time and distributes the data contained in the Composite tags to one or more associated tags.

(2) I do not understand why all these location metadata are in "Composite" tags and not written directly as XMP IPTC tags.
Furthermore, if they did not propagate, where would they be stored? Are they user-defined Exif Composite tags which can be recognized by any (modern) software?

When setting up the "standard" tags for IMatch (the list of tags you see in the "Standard" tab of the tag selector dialog) I tried to find the best tag for the job. Initially, I always used the Composite tags, because some of them come with some extra ExifTool magic attached which overcomes subtle differences and problems during write-back. Or just supports more output formats.

For some of the standard tags I had later to change to the original XMP tag because the testers found problems with using the Composite tags, or there were situations where ExifTool did something unexpected for some combination of options and output format. 

There is no ISO country code Composite tag, which is why I used the XMP tag.

Do you have a specific problem with IMatch using the Composite tags? Somethings not working?

[Gennaro]

Thank you for your reply, it's all much clearer now.

I'm not having any specific problem with IMatch and Composite tags, everything seems to be working fine.

I am somewhat of a beginner and the use of Composite tags was not very clear. There doesn't seem to be anything on the help file and I couldn't find that much google-ing around either. In particular, it wasn't clear why location tags had to be Composite, and the fact that some are Composite and others (well, just one) are XMP can be a bit confusing.

thanks
Gennaro

[jch2103]

It's useful to have the observations of a new user to the wild and wooly world of metadata that IMatch exposes. Perhaps you should submit specific suggestions to Mario about the Help file (via the Send Feedback about this help topic' at the bottom of each Help page).

[Mario]

The idea of the standard tags I've implemented for IMatch (there is a big section on that in the help) was to hide some of the grittier details of metadata processing from the user. I tried to find the best working ExifTool tag to 'fill' the standard tag, and sometimes IMatch looks at three or four ExifTool tags to make up a standard tag. Users are supposed to use Standard Tags where possible, and to use the native XMP, EXIF, GPS, IPTC etc. tags only for specific purposes. This gives metadata a much friendlier interface. Unless you look at the tooltips in the MD panel or use the Tag selector dialog to directly select tags, you are shielded to some extent from the actual tag names.

If IMatch would present a restricted view on metadata similar to other tools, I could hide all the tag business entirely behind a nice and limited number of metadata elements. But this is IMatch and my users expected that they can go down to the metal if required. Even casual users run into situations where they have to work with the real tags, complex maker notes and suchlike to solve a specific problem they have. And in IMatch, they can.

Over the Alpha and this Beta I had to change the tags used to form the standard tags several times, because users discovered subtle problems caused by specific combinations of Composite tags and file formats / metadata formats. Since all standard tags are controlled by an XMP configuration file, this is easy to do and every feature in IMatch, from the MD panel to scripting, will automatically use the new tag definition.