Altitude......

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So, this morning I set up a waypoint mission along a river for a couple hundred yards and then lifted the P4 up over the trees and circled back towards take off/start of the mission and ending it to form a sort of question mark shape. At the start of the mission, I was approximately 15 or 16ft off the water but 6ft above take off (on the bank) and the altitude reading was 6ft. At the end the mission, the altitude reading was 256ft. Don't know if it matters, but where I ended the mission, the land is about 40ft higher than the take off. I then flew back to the start of the mission (let the P4 fly itself about half way and then took over) and brought it down closer to the river as I approached the start. But at the point where the P4 looked like it was back to 15ft off the water, the altitude reading was 22ft instead of 6ft..... At that point I wasn't sure if the altitude reading was off, or if it had switched from altitude over take off to altitude over the land/water below, but even if it had, the 22ft still seemed too high. Unfortunately, being a newbie I didn't think to check the VPS. Anyhow, I decided not to run the mission because if the drone used 22ft as it's altitude when it was really at 15ft (over the water, 6ft over take off) and dropped to the start point altitude of 6ft, it would drop into the water.

Later today I was flying over a field (no mission) and lifting the P4 over the trees at the end. When I started over the field, it was 15ft off the ground (that was the reading and it appeared accurate) and I then brought it up to 200 or so as I cleared the trees. But when I brought the P4 back around and dropped back down to the field, at the point where the altitude reading was 25ft, the VPS indicated 6ft (I thought to look at it this time...) and visually the VPS was the correct reading......

Is the altitude reading really this variable and inaccurate, or is something else going on?

Thanks and sorry for the long post, but I wanted to include as much detail as possible.

Cheers,
Scott
 

msinger

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It's not uncommon for the altitude to be off since it's just a calculation. The altitude reported by the VPS is usually pretty accurate since it's using sensors to determine the altitude. Try calibrating the IMU on a level surface to see if that resolves your issue.
 
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I don't know, but mine starts at zero and then fluctuates during the flight over flat land with about a 20 minute flight. Flying straight and level it may show 20 feet, then drop to zero feet. Back to starting point and landing it shows -30 feet. This is with Go 3 on iOS ver. 9.3.5 and P4 all updated. Weird. I don't know what effect this bizarre altitude drifting would have on some autonomous flight app.

I installed the new RC 1.8 and ran through all compass, IMU, and VPS calibration with Assistant 2 (ver.1.0.6) and will check same flight path next week and see if it's any better.
 
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Meant to ask before, altitude is based on the take off point, right? And is there a way to switch it to based on the topographical elevation directly below the P4? Anyhow, the altitude variance is something to consider in regards to low altitude waypoint flights. We'll see after I re-calibrate the IMU if there's an improvement, but if not, then it seems like anything under 30ft or so for a waypoint might be dicey....

Had another, unrelated, waypoints mission scare a couple days ago. At the end of plotting a mission on the same stretch of river, but ending it still down at river level, when I started the mission and initially hit "ok" for the P4 to fly itself to the start (thinking I would take over), the app then froze during the uploading waypoints screen...I couldn't cancel the upload or do anything else, either with the app, or the controller. Fortunately, even though it cut across a curve in the mission path that followed a bend in the river, the P4 barely - like by a couple feet - missed the trees on the inside bank.... Then when it got to the start of the mission, I noticed that only the first waypoint showed on the map, but the P4 flew all 5 that I plotted. At the end of the mission, I finally regained control.

If that weren't enough, here's a pic of my P4 rescue at the same point on the river on Monday. This time it was just bad flying on my part. Took off and headed up the river, as I'd done a bunch of times already, looked away from the screen for a second, looked back and there was the branch up lose and personal. Guess it wasn't solid enough for obstacle avoidance. Anyhow, neck deep where the ladder is set and it's mid-October in northern NH....Oh yeah, and the branch started to crack just as I got to the P4... It came through unscathed and dry, me not so much.
 

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Meant to ask before, altitude is based on the take off point, right? And is there a way to switch it to based on the topographical elevation directly below the P4?
No ... Except for close to the ground readings with the VPS, the altitude data comes from a barometer which has no way of telling what is below it.
 
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Meant to ask before, altitude is based on the take off point, right? And is there a way to switch it to based on the topographical elevation directly below the P4? Anyhow, the altitude variance is something to consider in regards to low altitude waypoint flights. We'll see after I re-calibrate the IMU if there's an improvement, but if not, then it seems like anything under 30ft or so for a waypoint might be dicey....

Had another, unrelated, waypoints mission scare a couple days ago. At the end of plotting a mission on the same stretch of river, but ending it still down at river level, when I started the mission and initially hit "ok" for the P4 to fly itself to the start (thinking I would take over), the app then froze during the uploading waypoints screen...I couldn't cancel the upload or do anything else, either with the app, or the controller. Fortunately, even though it cut across a curve in the mission path that followed a bend in the river, the P4 barely - like by a couple feet - missed the trees on the inside bank.... Then when it got to the start of the mission, I noticed that only the first waypoint showed on the map, but the P4 flew all 5 that I plotted. At the end of the mission, I finally regained control.

If that weren't enough, here's a pic of my P4 rescue at the same point on the river on Monday. This time it was just bad flying on my part. Took off and headed up the river, as I'd done a bunch of times already, looked away from the screen for a second, looked back and there was the branch up lose and personal. Guess it wasn't solid enough for obstacle avoidance. Anyhow, neck deep where the ladder is set and it's mid-October in northern NH....Oh yeah, and the branch started to crack just as I got to the P4... It came through unscathed and dry, me not so much.
I can't help you with your situation but I must say that your framing and content of the picture is very nice even with the ladder!
 
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Ha! Thanks but only by chance, that shot was after I got it down and in my nearly hypothermic state, I wasn't thinking too much about framing....:)
 
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Is there any way to prevent these large variations in reported altitude readings? I've noticed this more with my P4 than P3P... but it really hit home for me this morning... I flew a simple waypoint mission clearing 12 feet tall brush by at least 10 feet. I flew the mission several times with my P3P with no issue. However, when flying the same exact mission with the P4... after one pass with no issue, on the second mission (with Litchi iOS) [and having not landed between running missions], it actually clipped the top of the brush. Fortunately it didn't crash, and simply hovered as I switched into Sports mode a little too late--after the horses had already left the barn. Sure enough, when I looked at it's reported altitude, with VPS indicating 9 feet above the level I took off from, the altimeter was showing 25 feet.
 
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Meant to ask before, altitude is based on the take off point, right? And is there a way to switch it to based on the topographical elevation directly below the P4? Anyhow, the altitude variance is something to consider in regards to low altitude waypoint flights. We'll see after I re-calibrate the IMU if there's an improvement, but if not, then it seems like anything under 30ft or so for a waypoint might be dicey....

Had another, unrelated, waypoints mission scare a couple days ago. At the end of plotting a mission on the same stretch of river, but ending it still down at river level, when I started the mission and initially hit "ok" for the P4 to fly itself to the start (thinking I would take over), the app then froze during the uploading waypoints screen...I couldn't cancel the upload or do anything else, either with the app, or the controller. Fortunately, even though it cut across a curve in the mission path that followed a bend in the river, the P4 barely - like by a couple feet - missed the trees on the inside bank.... Then when it got to the start of the mission, I noticed that only the first waypoint showed on the map, but the P4 flew all 5 that I plotted. At the end of the mission, I finally regained control.

If that weren't enough, here's a pic of my P4 rescue at the same point on the river on Monday. This time it was just bad flying on my part. Took off and headed up the river, as I'd done a bunch of times already, looked away from the screen for a second, looked back and there was the branch up lose and personal. Guess it wasn't solid enough for obstacle avoidance. Anyhow, neck deep where the ladder is set and it's mid-October in northern NH....Oh yeah, and the branch started to crack just as I got to the P4... It came through unscathed and dry, me not so much.
Interesting. I live in the Nevada High Desert, HAAT is over 4000 feet. The bird seems to calculate my altitude based on what the barometric pressure sensor tells it. Interesting that even though I'm 4000 feet above sea level, when I fire up the bird in the house, the altitude is recorded as 65 feet, which is stupid. I don't trust the displayed altitude. The system seems a bit primitive. We don't all live at sea level.
 
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Interesting. I live in the Nevada High Desert, HAAT is over 4000 feet. The bird seems to calculate my altitude based on what the barometric pressure sensor tells it. Interesting that even though I'm 4000 feet above sea level, when I fire up the bird in the house, the altitude is recorded as 65 feet, which is stupid. I don't trust the displayed altitude. The system seems a bit primitive. We don't all live at sea level.
In all fairness... the barometer isn't calibrated to pressure altitude at sea level--it just compares the pressure from the pressure it sensed from where it was turned on. Unfortunately, the two P4s I've flown, seem to have barometers that are less accurate than GPS-altitude (which is pretty poor). Flying inside a house might also be a little confusing to it... Air bouncing off walls from the prop wash or even the AC kicking on and off could affect the air pressure enough to give some wild altitude readings.
 
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In all fairness... the barometer isn't calibrated to pressure altitude at sea level--it just compares the pressure from the pressure it sensed from where it was turned on. Unfortunately, the two P4s I've flown, seem to have barometers that are less accurate than GPS-altitude (which is pretty poor). Flying inside a house might also be a little confusing to it... Air bouncing off walls from the prop wash or even the AC kicking on and off could affect the air pressure enough to give some wild altitude readings.
That's reasonable. Thank you.

Cheers
 
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Looks like this thread has had a birthday since it was updated :) Anyway, I was out flying my new (to me) P4P and began paying attention to the on screen telemetry. This is only my second session with the new bird so its all a bit new to me. It flies and answers the stick controls in awesome fashion however I did notice that the reported VPS altitude is not accurate. Ascending to 20 ft. looks okay at first. Take it up to 50 ft and it says 26 ft. Fly it forward a few meters and it bounces up to a higher number. Question is: is this an inherent flaw in the P4P? Is my drone defective? Very concerned
 
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Looks like this thread has had a birthday since it was updated :) Anyway, I was out flying my new (to me) P4P and began paying attention to the on screen telemetry. This is only my second session with the new bird so its all a bit new to me. It flies and answers the stick controls in awesome fashion however I did notice that the reported VPS altitude is not accurate. Ascending to 20 ft. looks okay at first. Take it up to 50 ft and it says 26 ft. Fly it forward a few meters and it bounces up to a higher number. Question is: is this an inherent flaw in the P4P? Is my drone defective? Very concerned
VPS is limited to 33 feet. Your drone works fine.
 
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Gotcha.....Vision Positioning System....not vertical position. Sorry about that. Thanks for setting me straight. I was hoping there was a way to verify current altitude during flight. If there is, I'm not seeing it.
 

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I was hoping there was a way to verify current altitude during flight. If there is, I'm not seeing it.
The current altitude displayed in DJI GO is always just the altitude above the takeoff point (not the Phantom's current location). When close to the ground, the VPS altitude is the best number to use since those sensors can "see" the ground. When not close to the ground, you should use your eyes to verify your Phantom is flying above all obstacles (or at least study the terrain in the flying area ahead of time so you know what to expect).
 
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Understood, I would think that since the FAA has placed limits on altitude during flight, that there would be a readout for that. They sure make it plain enough that there are airfields nearby and their exact location. I actually have air traffic over my house from a controlled airport about 10 miles away. I don't need the "see and avoid" lecture, I am a private pilot and part 107 licensed as well. I get that. Just seems like an altimeter would make a lot of sense since we have all these other instruments available. As a private pilot, I would not consider starting the engine without a working altimeter.
 

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I actually have air traffic over my house from a controlled airport about 10 miles away. I don't need the "see and avoid" lecture, I am a private pilot and part 107 licensed as well.
I'm not lecturing. You asked what options were available ;)
 

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