Time Zone Offset fonction

[pdominique]

Good morning
I use an external GPS (etrek30) to track coordinates/altitude data for my pictures. I recently came back from a backpacking trip in California (I live in Montreal). My camera was set properly to the local time at that time (-3 hours from Montreal), so the images are showing the proper creation time. When mapping my photos with the GPS track log I noticed that the altitude data was wrong... After reviewing the images from the map view, I figured out that it is a time zone issue. When doing the mapping which "Time" does LR use? Original creation time? Current location time?? or GMT time??? As the track log from the gpx file contains different time information. It seems that the Time zone offset function" is what I need to use, how do I make the proper adjustment. Do I offset from a GMT stand point (-7hours) or from the time zone difference (-3hours).???
Furthermore, I am not quite sure what happens when using the [Reset] button with time zone offset either... I noticed that once used, it now shoes the info in red but I am not sure how the correction applies to the first adjustment... can you clarify ?
As a side question to this problem, as a test, I have erased the current information showing in the GPS coordinates and Altitude fields, will I be able to auto-tagged the series of pictures all at once as I usually do ? As it seems that I could not remove the info (GPS coordinates and Altitude) all at once even when many images were selected, the change was applied to the first image only ... did I do it wrong... then I chose to do it manually one by one for a group of images but I have about 500 images from that trips !!

Thank you
Pascale

 

[clee01l]

Welcome to the forum. GPS altitude values are almost always wrong unless you have an extremely sensitive (expensive) instrument. First, the GPS measures the height of the instrument with respect to the geoid not MSL. The geoid is an imaginary surface of the Earth that measure a constant gravity reading Sometimes the geoid imaginary surface can even be above the instrument (i.e. below sea level). Second, the accuracy of a GPS wrt altitude is probably +/-30m. And lastly, if your instrument is located in deep valleys, the GPS signals can bounce giving you false readings. If the track log shows you to be fairly close to the physical point on the map where you actually were. You should consider it "accurate".

The GPS gets it's time signals from the satellites and can (but not necessarily) correct the time in the camera. Setting the time in the camera is a function of the camera and it's capabilities. With most DSLRs, you set the current local time, DST flag and the time zone. This causes a GMT timestamp and a local timestamp to be entered in the proper fields of the EXIF. If after you import these images into LR you want to adjust the capture time, you can use the Edit Capture Time function in the Library Metadata submenu to correct the capture time to the local time where the photo was taken. This is all you can do in LR and all you should need to worry about.

 

[pdominique]

Time zone followingup

Thank you Clee,
I understand you are saying but, I am sorry to say that I must not have been clear in my question... Yes GPS data are not 100% accurate, yes I set the proper time to my camera and made sure it was in synch with my GPS time when I landed in California... As well, to check the info regarding the altitude, I looked for a known landmark...Mount Whitney is at 14,496 ft elevation, the waypoint I took when I reached the summit shows it at 14,470 feet so give or take a few feet and a GPS accuracy of about 10 feet (that is usually what I get with my GPS especially with a clear line of site) and depending where I was when I took the waypoint that is not so bad. Now the oterh data I check was the time, It was close to 11h (California time when I took the picture), when I look in the metadata of the Date Time created my picture shows close to 11h00 as well. That is why when looking at the picture on the track log in MAP module I was surprise to see that the picture is not showing on Mount Whitney but rather where I was about 3 hours earlier that morning, so looking back at the metadata that I had mapped in LR Map module I saw that altitude and coordinates data were wrong. That is why I am wandering which time zone LR uses when mapping a "loaded tracklog" so that I can use the function offset time zone

to get the proper mapping and the good coordinates, as I believe that is probably the way to solve the problem.... I did try looking in the help menu but could not find anything for Time Zone Off set.... I could try doing some tests by creating a new catalogue to import some pictures and loading the tracklog and playing around the time zone offset function... but I would rather understand how it works so that the next time I am in a different time zone I do it before I tag all the pictures

Thank you again
Pascale

 

[pdominique]

Hello again
I did manage to correct the data... I though I would share what I done, if somone else is faced with he same problem... Since it seem to be off set by 3 hours, I deleted all coordinates and altitude data (I did manage to delete them all at once), I edited the name of the tracklog so that I could load them over as a new tracklogs, then I use the offset correction screen shown in my previous comment and off set it by 3 hours to reflect the time zone difference between my current location (Montreal) and the original creation location (California) .. then I re-mapped the pictures with the auto tag function, and now all is correct.. my pictures at Mount Whitney do show an altitude of 14,470 ft as the GPS track log... Now why is LR reading the current location time zone instead of the original creation location time zone is a puzzle... may be is is the way the data is save in the GPX file .. A question for Garmin (the GPS manufacturer;-)
Thanks again Pascale

 

[T20]

Time Zone off ser

I have the same problem, and do not the solution yet

 

[T20]

Time Zone off set

I have the same problem, and do not the solution yet