Why?? "Warning: No writable tags set" error message [SOLVED]

[quixote]

I've searched and searched and can't understand what I've found well enough to solve my problem. I have a camera without GPS. I use a gps logger to get coordinates with time stamps. Then (usually) I use gpicsync to enter the coordinates into the photo metadata.

Gpicsync kept telling me there was "no DATE/TIME in original" which is wrong. Other graphics programs (eg gwenview, aftershotpro) see original time. I checked it with exiftool itself and, using "exiftool -s -time:all *.CR2" it reported, for instance, for one of the files:

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======== IMG_7630.CR2
FileModifyDate                  : 2017:03:16 23:21:30+13:00
FileAccessDate                  : 2018:08:26 10:43:57+12:00
FileInodeChangeDate             : 2018:02:10 17:14:54+13:00
ModifyDate                      : 2017:03:16 10:21:30
DateTimeOriginal                : 2017:03:16 10:21:30
CreateDate                      : 2017:03:16 10:21:30
TimeZone                        : +12:00
TimeZoneCity                    : (not set)
DaylightSavings                 : Off

So I tried to use exiftool to put in the gps data directly, without the gpicsync frontend. Using this command

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exiftool -geotag ~/20170316.gpx '-geotime<${createdate}--7:00' ~/photos-2017/367_0316/*.JPG (California, UTC -7, and the logger uses UTC, hence the correction factor.)

And got this error message for each file (only the last one shown below):

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Warning: No writable tags set from /home/mm/IMG_7630.JPG
    0 image files updated
   17 image files unchanged

(I have the same problem whether I try to work with CR2 (RAW) files or jpgs.)

What's going on??? Why are the tags readable but not writable? How can I make them writable? How can I make sure this problem, whatever it is, doesn't happen again???

Thanks for any help and for a great exif-editing program!

[StarGeek]

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exiftool -geotag ~/20170316.gpx '-geotime<${createdate}--7:00' ~/photos-2017/367_0316/*.JPG

If you're using this command, you have 2 hyphens in front of the time zone, there should only be one.

Are you sure there are time stamps in the gpx file?  You can run exiftool on it and see if you have GpxTrkTrksegTrkptTime tags. 

This error usually is a timing issue.  The times in the gpx file should be (hope my math is right) in the area of 2017:03:16 17:21:30 ± 30 minutes for it to track right.

Finally, while it shouldn't be part of the problem, the TimeZone in your listing is +12:00, not -7:00.  It shouldn't be a problem with the geotrack as that should be a Canon Makersnote tag, which I don't believe exiftool checks when it looks for time.  But it does make me think that there is timing problems.

[quixote]

I opened the gpx file in kwrite (I'm running Debian + kde) and there are time stamps there.

I checked the command I'd run and sure enough, two hyphens. Running it with one hyphen ... it magically works!

Man. How embarrassing.  But totally delighted the problem is solved.

I was also convinced it was a timing issue and spent hours triple checking the photo and gpx time stamps, time differences, etc, etc, etc. I noticed that timezone +12 listing rather than -7. The only thing I can think is that the OS is convinced the computer's timezone should override the camera's? The pictures were taken in California, but I'm now in New Zealand and I'm not sure I've accessed them since they were taken. It seems completely nuts for the OS to mess about with a file's timezone, and it would definitely be a bug not a feature, but it's the only thing that makes any sense. NZ is UTC+12.

Thanks again for your help!