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Author Topic: Map module misplacing photos  (Read 1289 times)
Rhossydd
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« on: July 18, 2013, 06:54:34 AM »
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Trying to tag image location data to some photos from gpx data and LR 4.4.1 is getting the locations incorrect.

Photo in LR shows it was taken at 14:18:34 (it's a photo of GPS unit recording a waypoint. Taken to record actual error between camera and GPS = -15seconds read from GPX data)

Use LR to tag photo from the GPX track and it misplaces the image. Change the time zone offset to -1hrs and it gets the location correct.
If the camera time and log time are near enough identical shouldn't it get the location correct ?

What's going on here ? Is LR somehow automatically using location data to determine was it thinks should be the correct offset and applying that regardless ?


W7
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wolfnowl
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« Reply #1 on: July 19, 2013, 03:03:30 PM »
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Don't know your answer, I'm afraid, but using Google My Tracks I discovered that the .gpx data itself was off by 24 hours.  The date was correct on the filename, but the actual data was out.  Really confused me the first time as LR told me none of my images matched the track.

Mike.
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Adele
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« Reply #2 on: July 25, 2013, 06:19:31 PM »
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I had the same problem, and found the answer in Victoria Bampton's Lightroom 5 FAQ - "GPX logs,by definition, are time stamped in UTC (Coordinated Universal Time), whereas photos are usually stamped in the local time."  So you almost always have to adjust the GPX time in the Map module.  Adele
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Rhossydd
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« Reply #3 on: July 26, 2013, 02:11:13 AM »
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"GPX logs,by definition, are time stamped in UTC (Coordinated Universal Time), whereas photos are usually stamped in the local time." 
As far as I can see there's no indication of time zone in the camera EXIF data. So it still doesn't make sense to me why LR would think that 14:34 on the camera would be any different to 14:34 in the GPS data.
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Robert55
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« Reply #4 on: July 26, 2013, 02:50:50 AM »
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Adele is right.
The underlying problem is that there are 4 actors involved in this:
- the gps has a time + timezone + DST offset [and can be assumed to be right;
- the camera has a time, but unless you can set those not a timezone / DST stamp. Older Canons have neither, in my NEX they can be set.
- OS: don't know about the others, but Windows can [and is usually set to] check the time and place through an internet connection
- LR in itself has no clock; it takes its time from the operating system
I think the problem you are seeing is in the way the OS handles DST

BTW: I don't use LR for adding gpx data to exif. I use Geosetter [which uses Exiftool]. Already used it before the Map module was added, saw no reason to change. It is an extra step, but for me it is more flexible. While the Sony allows for hour shifts, it can't handle oddball timezones like Kathmandu (UTC +5.45 IIRC).
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Rhossydd
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« Reply #5 on: July 26, 2013, 02:58:41 AM »
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I think the problem you are seeing is in the way the OS handles DST
The problem here seems to be LR is making assumptions about time zones that aren't correct.
If camera time = GPS time there shouldn't be a need for any offset. It ought to be that simple.
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mlewis
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« Reply #6 on: July 26, 2013, 03:30:15 AM »
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The problem here seems to be LR is making assumptions about time zones that aren't correct.
If camera time = GPS time there shouldn't be a need for any offset. It ought to be that simple.
It is that simple if the camera clock is set to UTC.

GPS data always uses UTC (GMT) time.  The EXIF spec doesn't allow for time zone data so geotagging software doesn't know what time zone the camera clock is set to - it has to guess.  Exiftool assumes it is the same as the system it is running on and compensates accordingly. I use exifttol for geotagging and if I am doing the geotagging in a different time zone to where the photos were taken I have to remember to change the system clock to match the photo time zone.
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Robert55
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« Reply #7 on: July 26, 2013, 04:43:41 AM »
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I use Geosetter as GUI for Exiftool. Camera is set to local time. In Geosetter I add the timezone stamp, and then the gps location data. These are saved to an xmp sidecar file which is recognised by all SW I've used. No need to do anything else.

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Adele
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« Reply #8 on: July 28, 2013, 01:32:54 PM »
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The gpx logs themselves provide only CUT (Coordinated Universal Time - which is roughly equivalent to GMT) - they do not have have any adjustments for local time.  Various devices/software programs can convert the gpx data to local time.  In the case of a GPS device, the device makes the calculation.  In the case of LR, you need to tell LR the number of hours difference the local time is from CUT.  LR then matches the images to the tracklog by adjusting CUT by the required number of hours and matching the images based on the local time as recorded in the camera metadata. 

Hadn't heard of Geosetter - will check it out.

Adele
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