When you import photos into HoudahGeo, it asks about your camera clock settings. HoudahGeo needs accurate time information so it can match photos to GPS tracklogs. Thus HoudahGeo needs to know what time zone your camera clock was set to and if the clock was going slow or fast.
Let’s look at an example. You traveled to Croatia but left your camera clock set to UK time. The camera had been left unused for a while and the clock is going 5 minutes fast.
While in Croatia, you took a picture at 2:00 PM. Since Croatia is one hour ahead of the UK, your camera should think the picture was taken at 1:00 PM. The clock is also going fast, so the time recorded on the photo is 1:05 PM.
When you get to geotagging, you just need to tell HoudahGeo: the “camera was set to Europe/London” and “was going 5 minutes fast”. HoudahGeo will figure out the photo was taken at 1:00 PM UK time. This is correct, Croatia is 1 hour ahead, making 1 PM in the UK the same as 2 PM in Croatia.
There is a different way to reason. You could say “the camera was set to Croatia time” and “was going 55 minutes slow”. That is how you saw it when you looked at the camera while traveling. The camera clock was way behind.
You can give HoudahGeo that information: “the camera clock time zone is Europe/Zagreb” and the “clock going 55 minutes slow”. HoudahGeo will come to the same “moment in time” for the time on your photo: 2:00 PM in Croatia. With either settings, HoudahGeo can proceed to geocode and later to write accurate time information to your photo.
Which setting you use, is a matter of personal preference. With the first method, you stick close to the camera time. HoudahGeo will barely change the time on the photo. It will only adjust it to correct the 5 minutes of clock error. Then it will add the information that this is UK time.
With the second method, HoudahGeo adjusts the time recorded to metadata to match time in Croatia. This can seem more natural. The photo was taken at 2 PM local time. Now the metadata actually says so. HoudahGeo will, of course, add information that this is to be read as Croatia time.
Display Time Zone
No matter which approach you choose, HoudahGeo will know the exact moment in time the photo was taken. This allows HoudahGeo to match the photo to a GPS tracklog and figure out where it was taken.
While working in HoudahGeo, you may find it easier to relate to timestamps when these are shown as local time at your destination. In our example, this would be Croatia time.
For that purpose, HoudahGeo has the concept of “Display Time Zone”. This is set from the View menu or the menu in the top right corner of the project window.
Set it to “Europe/Zagreb” to see all times on images and tracklogs shown as Croatia time. The photo from the example will show a 2:00 PM time.
It is important to note that changing the display time zone does not change the times on the photos or in any other way affect the geotagging process. It just changes how times are displayed: the very same moment in time can be shown as 1 PM UK or 2 PM Croatia time.