ExifTool Forum

ExifTool => The "exiftool" Application => Topic started by: hrpunio on October 30, 2017, 05:30:52 AM

Title: Magic behind -geosync
Post by: hrpunio on October 30, 2017, 05:30:52 AM
Hello,
My camera uses CET time / GPS uses UTC time.
When geosyncing images I put time offset without UTC and photos are geotagged correctly, ie:

exiftool -geosync=-00:02:27 -geotag ... etc...

actual offset is -(3600 + 147s)

The question is how exiftool knows the time zone as there is no TZ information
in Date/Time Original and I cannot find any tag which explicite contains TZ, ie:

Date/Time Original              : 2017:10:29 11:17:12

--tomek
Title: Re: Magic behind -geosync
Post by: Phil Harvey on October 30, 2017, 07:23:29 AM
Hi Tomek,

ExifTool uses the system time zone if not provided.  (Read the geotime documentation here (https://exiftool.org/geotag.html#geotime).)

- Phil
Title: Re: Magic behind -geosync
Post by: hrpunio on October 30, 2017, 11:57:30 AM
Hello Phil
Thanks for explanation.
So it seems to me it would be safer to use time shift explicitly using
GPSTIME@IMGTIME
namely
-geosync=19:32:21Z@14:31:49-05:00
syntax? Just in case system time is not in sync with camera

--tomek
Title: Re: Magic behind -geosync
Post by: Phil Harvey on October 30, 2017, 12:02:36 PM
Sorry, I wasn't clear about the difference between -geosync and -geotime.

To be safe you should specify the time zone in the -geotime option.  A -geosync time zone (if given) is only used to calculate a time difference that is applied to the -geotime value.  The -geotime time zone (or system time zone if not otherwise specified) is used in calculating the absolute time for interpolating the position.

- Phil