Top Altitude Definition???

[benthinking08]

Howdy folks from the great southern state of Tennessee!!!

I'm hoping you can help me with something. I've searched the forums for some insight to this topic but can't find anything.

On the flight log page of the my DJI GO app, there is a heading for "Top Altitude". What is that referring to???

I know, I know, I know...It seems self-explanatory. But it clearly is NOT an indication of the highest altitude I've reached AGL nor ASL. My typical launching point (as well as my highest launching point) is at 213 ft ASL. My lowest launch was from the beach at 0 ASL. I can assure you... I've NEVER flown ANYWHERE near 8,000 ASL!!! The highest I've ever flown is around 500 AGL (equal to 713 ASL). Even if I translate it to metric, the max altitude I've ever actually flown would be around 2,300 meters (forgive me if I screwed up the conversion of those numbers. I'm just a Yank who hasn't had to deal with the metric system very often...Lol).

So...The "Top Altitude" is befuddling me. Can anyone advise?

Thanks and DRONE ON!!!

-Scoop

 

[Meta4]

On the flight log page of the my DJI GO app, there is a heading for "Top Altitude". What is that referring to???

The highest I've ever flown is around 500 AGL (equal to 713 ASL). Even if I translate it to metric, the max altitude I've ever actually flown would be around 2,300 meters (forgive me if I screwed up the conversion of those numbers. I'm just a Yank who hasn't had to deal with the metric system very often

First the easy one to answer is you went the wrong way with the metric conversion .. it would be 217 metres (think of a meter as just a bit more than 3 feet)

The top altitude showing on mine turns out to be the height above sea level of my highest flight up in the mountains.
Look at where it says Top Altitude and it will give the date of that flight so you can see what it is referring to.

 

[sar104]

First the easy one to answer is you went the wrong way with the metric conversion .. it would be 217 metres (think of a meter as just a bit more than 3 feet)

The top altitude showing on mine turns out to be the height above sea level of my highest flight up in the mountains.
Look at where it says Top Altitude and it will give the date of that flight so you can see what it is referring to.

I don't see anything labeled "Top Altitude".

In the flight records section, left pane, there is a "MAX TAKEOFF ALTITUDE" with a date, which is obviously the highest takeoff altitude above MSL (not the highest altitude reached during the flight) of all the flights in the flight list.

And in the flight records list in the right pane there is a "Max. Alt." column, which is the highest altitude reached in the flight above the takeoff point.

Both of those seem entirely self-explanatory.

There does not seem to be any record of takeoff altitude in the individual flight records, although that is in the detailed log files. I'm not sure whether the recorded MSL altitude is derived from barometric or GPS data but it should be easy to check by looking for log altitude entries after startup but before a GPS positional lock is acquired.

 

[Meta4]

I don't see anything labeled "Top Altitude".

It's probably something that DJI tinker with between versions.
The one I'm running shows Footprints,Top DIstance, Top Altitude, Top Speed in the laft side panel.

 

[aburkefl]

I don't see anything labeled "Top Altitude".

In the flight records section, left pane, there is a "MAX TAKEOFF ALTITUDE" with a date, which is obviously the highest takeoff altitude above MSL (not the highest altitude reached during the flight) of all the flights in the flight list.

And in the flight records list in the right pane there is a "Max. Alt." column, which is the highest altitude reached in the flight above the takeoff point.

Both of those seem entirely self-explanatory.

There does not seem to be any record of takeoff altitude in the individual flight records, although that is in the detailed log files. I'm not sure whether the recorded MSL altitude is derived from barometric or GPS data but it should be easy to check by looking for log altitude entries after startup but before a GPS positional lock is acquired.

Saw several references about MSL in this thread. Doesn't the "altitude" referenced with a Phantom be exclusively related to AGL (Above Ground Level)? I don't think there's sufficient electronics in the Phantom to truly identify altitude - it's strictly a matter of rrecognizing where you're starting as a "base point" (yeah, I know they call it the Home Point) and the numbers go up (or down from there).

A classic example is someone well up into the mountains who takes off and then flies over a cliff and starts going down. When that happens, your "altitude" numbers start going down and even into a negative range. That obviously wouldn't refer to altitude until your Phantom disappeared beneath the waves!

 

[sar104]

Saw several references about MSL in this thread. Doesn't the "altitude" referenced with a Phantom be exclusively related to AGL (Above Ground Level)? I don't think there's sufficient electronics in the Phantom to truly identify altitude - it's strictly a matter of rrecognizing where you're starting as a "base point" (yeah, I know they call it the Home Point) and the numbers go up (or down from there).

A classic example is someone well up into the mountains who takes off and then flies over a cliff and starts going down. When that happens, your "altitude" numbers start going down and even into a negative range. That obviously wouldn't refer to altitude until your Phantom disappeared beneath the waves!

The data presented during a flight is only altitude above the takeoff point (derived barometrically), but the flight logs unambiguously include both altitude above takeoff point and altitude above MSL.

In terms of determining altitude above MSL - that doesn't require any extra sensors or "electronics" (whatever you mean by that) than the aircraft already has. That altitude could be determined from the GPS data, since the aircraft always has a 3-D location solution in GPS mode, or it could be determined from the barometric sensor by comparison to a standard atmosphere.

 

[Meta4]

Saw several references about MSL in this thread. Doesn't the "altitude" referenced with a Phantom be exclusively related to AGL (Above Ground Level)? I don't think there's sufficient electronics in the Phantom to truly identify altitude - it's strictly a matter of rrecognizing where you're starting as a "base point" (yeah, I know they call it the Home Point) and the numbers go up (or down from there)

As mentioned above, the Top Altitude showing on my app (and for many others too) is the max altitude above sea level.
This is from GPS data which is recorded but not displayed in the app or used for flight functions.

 

[benthinking08]

I should have included this screenshot with my post.

According to the screenshot I just posted, I reached a maximum altitude of over 8,000 feet on April 26.

On April 26, I was at home where the elevation is 213 ft. ASL. There's no way I climbed to 8,000 ft ASL, AGL or any other **L that day.

Hope this helps to better illustrate my point of confusion.

Thanks for the replies!!!

 

[sar104]

I should have included this screenshot with my post.

According to the screenshot I just posted, I reached a maximum altitude of over 8,000 feet on April 26.

On April 26, I was at home where the elevation is 213 ft. ASL. There's no way I climbed to 8,000 ft ASL, AGL or any other **L that day.

Hope this helps to better illustrate my point of confusion.

Thanks for the replies!!!

Interesting - where your app lists "TOP ALTITUDE" mine (DJI GO 4 v4.1.3) lists "MAX TAKEOFF ALTITUDE", which is a bit more specific. I would guess that it is actually the same parameter in both cases though.

In your case, since you clearly did not take off at, or climb to, anything like that altitude, it must be an error. I would pull the flight log(s) for that day and check the flight data for altitude above MSL - you should be able to see exactly where the discrepancy arose.

 

[aburkefl]

The data presented during a flight is only altitude above the takeoff point (derived barometrically), but the flight logs unambiguously include both altitude above takeoff point and altitude above MSL.

In terms of determining altitude above MSL - that doesn't require any extra sensors or "electronics" (whatever you mean by that) than the aircraft already has. That altitude could be determined from the GPS data, since the aircraft always has a 3-D location solution in GPS mode, or it could be determined from the barometric sensor by comparison to a standard atmosphere.

Appreciate the clarification. I was trying to avoid referring to any Phantom as having a barometer - at least in terms of what you would find in a aircraft altimeter (which is basically a calibrated barometer). I forgot about the 3D coordinates you automatically get with GPS.

That's what I get for trying to "skirt" the edge of a technical discussion! LOL

Art - N4PJ
Leesburg, FL

 

[sar104]

Appreciate the clarification. I was trying to avoid referring to any Phantom as having a barometer - at least in terms of what you would find in a aircraft altimeter (which is basically a calibrated barometer). I forgot about the 3D coordinates you automatically get with GPS.

That's what I get for trying to "skirt" the edge of a technical discussion! LOL

Art - N4PJ
Leesburg, FL

The modern solid-state pressure sensors used in these devices (and also in watches, GPS units etc.) are actually pretty good at measuring absolute pressure. Once calibrated initially they don't drift much. And so while they are not calibrated to take account of local density altitude variations (as you would with an aircraft pressure altimeter), they can simply reference a standard atmospheric pressure model to derive an altitude, but it won't be as accurate as a good 3-D GPS altitude because it is unable to compensate for deviations from a standard atmosphere (temperature and pressure variations).

 

[benthinking08]

The modern solid-state pressure sensors used in these devices (and also in watches, GPS units etc.) are actually pretty good at measuring absolute pressure. Once calibrated initially they don't drift much. And so while they are not calibrated to take account of local density altitude variations (as you would with an aircraft pressure altimeter), they can simply reference a standard atmospheric pressure model to derive an altitude, but it won't be as accurate as a good 3-D GPS altitude because it is unable to compensate for deviations from a standard atmosphere (temperature and pressure variations).

Ummmm...You lost me at "The modern..." Lol

 

[aburkefl]

Ummmm...You lost me at "The modern..." Lol

Many times it's much simpler to use technical terms and make the answer very brief. At other times, the brief, technical answer may generate even more questions! I *was* going to deliver a concise description of density altitude. However, suffice to say, if you Google "density altitude" you'll discover a lot about what he was writing.

Have you ever heard on the news that it was so hot in Phoenix that they grounded passenger flights? Even pilots in small planes need to be aware of density altitude. And as for calibration, even in a small plane, one of the initial settings a pilot makes is to adjust his altimeter for the "local setting."

In truth, a lot of this stuff is downright fascinating and, armed with only a little of this knowledge, you can be entertaining (or incredibly boring!) at cocktail parties - "...well, if you had the kind of education I had..." LOL

Art - N4PJ
Leesburg, FL