I've flown several P4RTK in Terrain Follow mode and have discovered an important limitation which is potentially dangerous.
I imported my own high-resolution digital surface model (DSM) for the zone of interest. So far so good.
I set the flight height at 60 m above the digital surface model (= terrain + canopy height, since I'm above closed-canopy forest).
Flight lines follow the terrain, no problem. Works well. The problem is that when connecting between two flight lines during a mission, the drone DOES NOT adjust its height acccording to the DSM for that 'connecting line', and it just flies in a straight line between two points, not caring whatsoever about the DSM. This is potentially dangerous, since it could crash into the terrain or a tree when flying to connect two flight lines. Obviously I know you can use obstacle avoidance (and I do), but I'd rather have that as a backup rather than a primary way of avoiding crashing into obstacles when the drone flies between two flight lines.

It seems logical to me that the drone should follow the terrain during the ENTIRE mission, not just for the individual flight lines but also for those lines that connect two flight lines of the same zone.
I've seen this behaviour in 10 other Terrain Follow missions I've flown. Luckily 60 m was high enough that there were no obstacles to hit when the drone was flying between flight lines, but the expected behaviour should definitely be to track the terrain all the time, no matter if it's a main flight line or a line connecting two flight lines.

can you share with us one of your DSM ?

Here's a link to itthe DSM (.tif):
https://www.icloud.com/iclouddrive/0nGvzIe-v40yyy03MpGz5_Exw#DSM%5Fsbl%5FEPSG8237%5Fcroche
and the tfw file:
https://www.icloud.com/iclouddrive/0_syLKrmqC7e1Gsl0ilPZQWkQ#DSM%5Fsbl%5FEPSG8237%5Fcroche%5Ftfw

Ok maybe this is not the problem but first thing i see is a naming problem. TIF and TFW must have same file name

I have created a terrain follon plan with your dsm, i see no problem but of course im not flying over it. Sorry i cant help you. I use that function regularly, no problem at all.

Thanks. To clarify, the problem is not creating or flying the mission. As I mentioned, I successfully flew several missions. The mission you created contains no large connecting lines where the drone flies a longer distance two connect two non-neighbouring lines. This is when I see a problem. Drone flies in a straight line (not tracking terrain) only in those cases.

I haven't seen this either but have not flown a flight plan with long connecting legs where terrain variability could pose an issue when a straight line waypoint-to-waypoint path is followed.

But I wouldn't be surprised at all if this is a real issue- it smacks of the problems that have been reported where the DSM is not honored @ mission start...

DJI needs to fix these potentially catastrophic fight control safety issues ASAP.

elaliberte Posted at 9-3 13:25
Thanks. To clarify, the problem is not creating or flying the mission. As I mentioned, I successfully flew several missions. The mission you created contains no large connecting lines where the drone flies a longer distance two connect two non-neighbouring lines. This is when I see a problem. Drone flies in a straight line (not tracking terrain) only in those cases.

yes, understood