Thanks in advance

I Update my firmware

I am going to do a 2D Photogrammetry at 100m of height and I saw that this new option "Relative Height" appeared to me, before it was not.

Previously I had seen this option in 3D Photogrammetry (Double Grid)

Should I put a number?

What is it for?

Hi SUYDESA,

I haven't installed the new update yet, but I think that  RELATIVE HEIGHT is the difference in height between the take-off point and the mapped area, whereas RELATIVE ALTITUDE is the height above Home Point (i.e. the take-off point) at which the drone flies.

Unfortunately DJI uses five terms: Absolute altitude, Relative altitude, Mission Altitude, Flight Altitude and Relative Height.

In the P4RTK User manual you can read:
"There are two kinds of altitudes displayed in the DJI GS RTK app, absolute altitude and relative altitude.
Absolute altitude: The geographical attribute, in relation to longitude and latitude.
Relative altitude: The altitude data of the operation tasks relative to the Home Point. In the same operation, the absolute altitude for the same point during the operation will vary when taking off from locations with different elevations"  

and also...  

"Relative Altitude: The relative height between the takeoff point and the operation area. The actual operation height is the aircraft height minus the relative height. NOTE: Make sure to set the correct relative height to ensure the results contain appropriate overlap rates."

More detailed info (and a graph) can be found in the P4RTK FAQ page, "Software" section, Question 20 "In what cases do I need to adjust the relative height value?"  

Moreover in the DJI Terra FAQ page, "Flight and aerial images" section (see Question 5 and 6):
"The RELATIVE HEIGHT, in the advanced settings, is the elevation of the take-off point with respect to the mapped area. The MISSION ALTITUDE is the height of the drone with respect to the same area, and it is also the reference value with which the soil sampling distance (GSD) is calculated."

I think there is a misuse of the terms Altitude and Height.  In aeronautics ALTITUDE (ALT) is "the vertical distance of an object measured from mean sea level (MSL)", whereas HEIGHT is "the vertical distance of an aircraft above whatever SURFACE (buildings, mountains, a lake, etc.) (height above ground level or height AGL)".

Cheers,
Maurizio

Aloha SUYDESA,

     I do not have this program but I do have experience with DJI products and have a P4 and a P4 Pro.  Just looking at it and reading everything in the image, I would say you should determine what height you want to have as your base (engineering) height over the project area.  The program suggests 100 meters.  You could choose 85 meters since that is your maximum altitude and set each waypoint so it would be a minus number from that altitude.  But be sure to also enable the Altitude Optimization.  When you read the gray text below Altitude Optimization, you will see that it improves the accuracy of your project measurements.

     Hope this helps!

Aloha and Drone On!

Cetacean Posted at 4-3 01:13
Aloha SUYDESA,

     I do not have this program but I do have experience with DJI products and have a P4 and a P4 Pro.  Just looking at it and reading everything in the image, I would say you should determine what height you want to have as your base (engineering) height over the project area.  The program suggests 100 meters.  You could choose 85 meters since that is your maximum altitude and set each waypoint so it would be a minus number from that altitude.  But be sure to also enable the Altitude Optimization.  When you read the gray text below Altitude Optimization, you will see that it improves the accuracy of your project measurements.

Aloha Cetacean-

Hope all is well there.

While your contribution is certainly appreciated, as we've seen in other P4 RTK threads it's probably best to let those that actually have the kit answer questions regarding its workings and the specific apps for flight planning and execution. There are enough differences between them and the consumer models that experience with the latter does not always lead to proper conclusions.

I believe Maurizio's answer is spot-on.

Cheers!

patiam Posted at 4-6 08:53
Aloha Cetacean-

Hope all is well there.

Aloha patiam,

     You are right, Maurizio's answer is spot on.  It would have been nice if your comment here was a couple / three days earlier.  As I it is, Maurizio's comment is 12 minutes before mine and we were both a day or so late.  But, your critique is based on statistics, not actual fact.  You might want to take that under consideration in the future.

     Not all is at it appears to be.

Aloha and Drone On!

Cetacean Posted at 4-6 16:38
Aloha patiam,

     You are right, Maurizio's answer is spot on.  It would have been nice if your comment here was a couple / three days earlier.  As I it is, Maurizio's comment is 12 minutes before mine and we were both a day or so late.  But, your critique is based on statistics, not actual fact.  You might want to take that under consideration in the future.

Aloha Cetacean-

Wow, I'm sorry if somehow I hit a nerve there. In fact I DID pay attention to the timestamps. I'm not sure how relevant that is to the point I was trying to make, which is that for specialized kit like the P4 RTK,  the best information generally comes from folks with direct experience on it. I was merely offering an opinion for others to consider in the future. I'm very sorry if you took offense to my use of your post as an example/jumping off point.

I also don't know what you mean by "based on statistics, not facts". It is a fact that there have been several P4 RTK threads in which well meaning forum members that do not own nor have any experience with the P4 RTK  have offered answers to questions or hypotheses about how it works that have been inaccurate.

Again, I was not making a personal attack. The goal was to improve the SNR of the forum, not engage in a squabble. To that end, I'll wish you good health and safe flights.

patiam Posted at 4-6 22:27
Aloha Cetacean-

Wow, I'm sorry if somehow I hit a nerve there. In fact I DID pay attention to the timestamps. I'm not sure how relevant that is to the point I was trying to make, which is that it for specialized kit like the P4 RTK,  the best information generally comes from folks with direct experience on it. I was merely offering an opinion for others to consider in the future. I'm very sorry if you took offense to my use of your post as an example/jumping off point.

Aloha patiam,

     Mahalo for setting the record straight!

     Stay safe!

Aloha and Drone On!