Hi All,

I'm very new to both this forum and to Drone Photogrammetry in general. My company has just recently invested in a Phantom 4 RTK Drone and base station and I'm in the process of learning how to use it.

So far I've flown two missions, the first at a local park and the second at one of our project areas both with great results and am looking forward to using it more.

I'm currently planning our 3rd mission, to be flown over an existing minesite (now closed) but where we are looking to recommence operations in the future.

I want to explore using the Terrain Awareness Mode on our P4 RTK however I have a question which I am hoping the DJI community can help with.

I have been able to import DSMs into the remote and create flight plans based off this. The DSMs I have however are in the AHD vertical Datum and not Height above GRS 1980 (which I believe is the "GPS" altitude that the drone uses). At this particular location, AHD sits approximately 24-25m above GRS 1980.

My question is, when I've set the flight height for the flight plan to 100m in the Terrain Awareness Mode, will the drone fly at a height of 100m above my DSM, or will it fly at an altitude of 100m above the GPS height but make a correction based on the take off location/base station information? The terrain at this site varies by ~100m and we want to have a constant GSD across the entire survey area. This is important to us as we want the best GSD possible with the time/batteries available (ie. I don't want to fly at 125m above the ground).

I would be very keen to hear from anyone that has some knowledge or experience about this.

Thanks, I look forward to hearing from the community!

Hi,
P4R flies in distance to your dsm (tif you loaded into your controller). But be aware of the difference of the wgs84 geoid to "real" surface
https://www.unavco.org/software/geodetic-utilities/geoid-height-calculator/geoid-height-calculator.html
For my flights I did produce a tif plus the undulation of the region. This did work very well
Gernot

I have a question relating to operating height of the P4R when using terrain aware function:

I want to utilise the terrain awareness mode with my P4R drone. I did a test and did not get the results I expected.

Planning:
•        Generated a terrain model (GeoTiff) using 1 sec SRTM data from Global Mapper and loaded it into the controller via micro SD card
o        The DSM is in lat/long wgs84 ellipsoid
•        It imported as expected
•        Set the boundary of the flight area
•        Set height to 60m
•        Speed (m/s) 4.0
•        Imitation fineness (m) 10
•        The flight path summary showed the DSM surface to be approx. 470-515m AMSL and the flight path to be 530-575m AMSL (as expected as I had set flight height of 60m)

**Why can’t I load a DSM and overlay with a KML boundary? It is impossible to see through the DSM to ensure I am capturing the correct area.**

In the field:
1.        No RTK used (I use PPK processing method)
2.        Powered on the P4R at around 479m AMSL
3.        Loaded saved plan & checked settings (60m capture height)
Altitude showed 0m at power up; indicating altitude to be measured using take off position as datum
4.        It launched to 168m before transiting to first waypoint
NOTE: first waypoint was a few meters lower compared to launch location; no obstacles between launch and first waypoint
5.        What would cause it to launch so high?
6.        The flight height was set to 60m
7.        The site variation of the DTM is only around 50m
NOTE: I launched from the lower part of the site

I have tested this workflow on two sites and both instances the drone followed the terrain well during mapping however at 140m separation between loaded DSM and flight path rather than the planned 60m or 100m

Any tips for future operations to ensure planned capture height is actual height of operation in the field?

Heidi.G Posted at 12-1 22:00
I have a question relating to operating height of the P4R when using terrain aware function:

I want to utilise the terrain awareness mode with my P4R drone. I did a test and did not get the results I expected.

The drone uses the ellipsoid height rather than ASML (or in my case AHD), so I suspect that you may find your answer there. It possibly depend on however much of a difference there is between these two.

Hello everybody.

After using the P4RTK for 8 months, I really wonder why DJI hasn't come up with a better way for the terrain awareness flying mode.
I think that a good solution would be to use the normal planning mode, and have the possibility to then mark ( a box) that you want to use a terrain model. ( Of course you need to have a terrain model for the area, but you can load a big one up front, who covers the area )
Then you would be able to use a kml file and all of the options that are in the normal planning function.
That would ease up the planning and flying very much.

Heidi.G Posted at 2019-12-1 22:00
I have a question relating to operating height of the P4R when using terrain aware function:

I want to utilise the terrain awareness mode with my P4R drone. I did a test and did not get the results I expected.

Dear Heidi,

I have two problems using DSM:
1. it covers base map and I can not plan my flight because i can not see anything
2. if I try to use  kml to bound my area of interst , it is always mesage "kml exceeds... " no meter DSM is much more larger than KML. I checked booth separatly in RC and it looks well. Did you have such of troubles?

Best Regards!

Boki

Hello Boki! I have the same problem!

Heidi.G Posted at 2019-12-1 22:00
I have a question relating to operating height of the P4R when using terrain aware function:

I want to utilise the terrain awareness mode with my P4R drone. I did a test and did not get the results I expected.

Hello Heidi,
are you still not getting the right flight height and overlap? Or did DJI change the flight altitude calculation for Terrain Awareness?
I also want to fly in PPK mode with a 25 m EU_DEM from the Copernicus website and wondering if I have to add the undulation model to get the correct flight base height!?
But I think that DJI uses the WGS84 ellipsoid height of the 'normal' GNSS which can only be corrected with the RTK connection.
Thanks and best regards!
Steffen