I compared geoencoding of Houdah, PhotoMechanic6 and Gps4cam, and get very different results.
For the test I used a very precise tracklog with 30 sec intervals, and shot photos at precisely known locations, including several series of photos taken at a stationary spot.
To my astonishment Houdah and PhotoMechanic both did not recognise the photo series taken at a stationary location and gave them all slightly different coordinates, as if the camera had been traveling at a steady pace all along the entire track. Good old gps4cam wasn't fooled and got all coordinates correct.

What am I doing wrong?
Furthermore the results of Houdah and PhotoMechanic are not identical, and differ up to 5 seconds from gps4cam.

Grateful for any suggestions, thanks, E
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HoudahGeo uses linear interpolation between two points on the track log. Basically, this comes down to assuming you traveled at a constant speed between two points on the track log. In most cases, this is the most reasonable assumption.

You can fault the logic by spending the first 10 seconds of your 30-second logging interval at the starting point and taking pictures. Then you use the next 20 seconds to run to your next stop where your track logger marks the next track point. HoudahGeo will assume you spend all of the 30 seconds traveling between the two points. A photo taken at the 10-second mark will thus be placed one-third of the way towards the second track point. HoudahGeo can't know that you started moving only after taking that last picture.

You can improve accuracy by setting a shorter logging interval.

If you prefer to have all photos tagged to the exact same location, you can use waypoints. These are typically set by pressing a button on your track logger.

I don't know how the other two products work. One possibility is to assume that you spent 30 seconds at each track point and then instantly jumped to the next one. This will attach all photos to the track point closest in time. This solves your current problem but will cluster your photos in locations at 30-second intervals even when you are actually traveling. E.g. taking photos from a moving car will place your photos in clusters at 500m intervals. This gets much worse with longer logging intervals.
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