When you take the drone off from a high hill, the altitude show on your RC is 0. When you fly the drone away down from the hill, the altitude shows as minus.

  

Similarly, when I fly my drone from a pier and try to take photos above the water on vision distance, RC always shows minus altitude. In this case, I always worry about the drone drops in water.

  

My question is:

  

Whether it is possible the RC shows the actual altitude when you fly a drone in above situation?

All DJI drones show the altitude above the takeoff point. That altitude shows a negative value when flying below the takeoff point.

If you're flying a drone that has downward sensors (like the Mavic models), DJI GO will show the distance from the drone to ground if the drone is close enough for the downward sensors to detect the ground. If you're flying near the ground, that's the closest thing you're going to get to the current altitude. It's never 100% accurate, but it's acruate enough to determine when you're dangerously close to the ground.

msinger Posted at 2018-9-8 08:19
All DJI drones show the altitude above the takeoff point. That altitude shows a negative value when flying below the takeoff point.

If you're flying a drone that has downward sensors (like the Mavic models), DJI GO will show the distance from the drone to ground if the drone is close enough for the downward sensors to detect the ground. If you're flying near the ground, that's the closest thing you're going to get to the current altitude. It's never 100% accurate, but it's acruate enough to determine when you're dangerously close to the ground.

What you mean is that RC cannot  show the absolute altitude, but only relative altitude?  

djiuser_PEp4mLwh74c7 Posted at 2018-9-8 08:28
What you mean is that RC cannot  show the absolute altitude, but only relative altitude?

You're talking about two different things - the height from launch and the height according to the VPS sensors.  But the sensors are only good for about 10 feet or so from the ground.  There's no such thing as "absolute altitude" or "relative altitude."  The common phrases are MSL and AGL.  DJI uses the height above the launch point and calls it "altitude" but it's not really altitude.  It's really just a height reference from the launch point.  And in addition it has the VPS sensors which may or may not be working (due to excessive height) or be accurate.  If you want to know the actual height from the ground or water during your flight, it would be a good idea to plan your flight carefully and research surface elevation changes with a site that shows such data.  Good luck

Mark The Droner Posted at 2018-9-8 09:03
You're talking about two different things - the height from launch and the height according to the VPS sensors.  But the sensors are only good for about 10 feet or so from the ground.  There's no such thing as "absolute altitude" or "relative altitude."  The common phrases are MSL and AGL.  DJI uses the height above the launch point and calls it "altitude" but it's not really altitude.  It's really just a height reference from the launch point.  And in addition it has the VPS sensors which may or may not be working (due to excessive height) or be accurate.  If you want to know the actual height from the ground or water during your flight, it would be a good idea to plan your flight carefully and research elevation changes with a site that shows such data.  Good luck

Thank you for clarifying the concept.

It raises another question:
When you launch AC on a mountain with altitude 500m, FAA only allows 120m max.  When your AC reaches this height,  the actual height  is at 620m. Suppose you fly your drone down the mountain to a platinum with altitude 200M,  the actual altitude right now is 420m. Is this height legal or illegal?

Your post is confusing.  Remember - use AGL or MSL.

You write a mountain with altitude 500m, what do you mean?  Do you mean 500m MSL, or do you mean 500m from the base of the mountain?

When discussing FAA and height, it's best to use the acronym AGL.  

If you're on a mountain, you could fly straight up until you reach a limit of 120m AGL to keep the FAA happy.  If you fly out horizontally over the valley as most people would, you'd quickly find yourself more than 120m AGL even if your Go app shows 0 feet altitude.  So you would usually want to fly down into the valley.  Your altitude on the Go app would be a negative number.  

Most of DJI's current ACs can fly only up to 500m in height from the launch point.  

However, there's another restriction at 5,000m MSL or 6,000m MSL depending on the AC.  

I believe there's a restriction in DJI's negative altitude too.  I can't recall what it is.

Good luck

djiuser_PEp4mLwh74c7 Posted at 2018-9-8 08:28
What you mean is that RC cannot  show the absolute altitude, but only relative altitude?

I mean the altitude shown is always the altitude above the takeoff point. The takeoff point is at 0 feet. Other than when the downward sensors are able to detect the ground below, the drone has no idea how high it is above the ground.

If you took off from a side of a mountain, your actual height would not be the same as what the drones recorded elevation would be, after leaving the associated home point.


RedHotPoker

msinger Posted at 2018-9-8 12:03
I mean the altitude shown is always the altitude above the takeoff point. The takeoff point is at 0 feet. Other than when the downward sensors are able to detect the ground below, the drone has no idea how high it is above the ground.

This is exact what I want to know.

If the pilot doesn't know the altitude/elevation above mean sea level (AMSL), it is difficult to judge the height exactly, especially fly above the water .

RedHotPoker Posted at 2018-9-8 12:23
If you took off from a side of a mountain, your actual height would not be the same as what the drones recorded elevation would be, after leaving the associated home point.

Whether there is a way to know altitude/elevation above mean sea level (AMSL)?

When I launch my drone from a pier, and try to follow the boat on the bay, the RC shows -2m. I don't want to fly the drone into the water.  

djiuser_PEp4mLwh74c7 Posted at 2018-9-8 12:33
Whether there is a way to know altitude/elevation above mean sea level (AMSL)?

When I launch my drone from a pier, and try to follow the boat on the bay, the RC shows -2m. I don't want to fly the drone into the water.

Don’t fly down low.

Stay up, higher... ;-)


RedHotPoker

I’m curious as to whether the Altitude is measured by the Sensors or by GPS, makes more sense for it to be the latter

Latanzi Posted at 2018-9-8 12:43
I’m curious as to whether the Altitude is measured by the Sensors or by GPS, makes more sense for it to be the latter

Yes. It is necessary.

One shows the height to your home point
One shows the height of the drone current located.

I don't know whether DJI can do it or not.

djiuser_PEp4mLwh74c7 Posted at 2018-9-8 12:27
This is exact what I want to know.

If the pilot doesn't know the altitude/elevation above mean sea level (AMSL), it is difficult to judge the height exactly, especially fly above the water .

Yes, it can be difficult to judge the AGL altitude when not flying VLOS.

Latanzi Posted at 2018-9-8 12:43
I’m curious as to whether the Altitude is measured by the Sensors or by GPS, makes more sense for it to be the latter

It's estimated using the barometer in the drone.

djiuser_PEp4mLwh74c7 Posted at 2018-9-8 09:21
Thank you for clarifying the concept.

It raises another question:

When you launch AC on a mountain with altitude 500m, FAA only allows 120m max.  ... Is this height legal or illegal?
You need to understand the rules better.
The limit is 120 metres above the ground (below the aircraft).

Whether there is a way to know altitude/elevation above mean sea level (AMSL)?
Yes .. but the pilot has to do a little thinking and some mental arithmetic

Latanzi Posted at 2018-9-8 12:43
I’m curious as to whether the Altitude is measured by the Sensors or by GPS, makes more sense for it to be the latter

It would make no sense for altitude to be measured by GPS.
Because GPS is very inaccurate for altitude.

Labroides Posted at 2018-9-8 14:26
When you launch AC on a mountain with altitude 500m, FAA only allows 120m max.  ... Is this height legal or illegal?
You need to understand the rules better.
The limit is 120 metres above the ground (below the aircraft).

Seems no people got what is the major I concerned.

Suppose you fly the drone down from a hill.  Could anyone tell me what will be the height of the drone to the ground?

djiuser_PEp4mLwh74c7 Posted at 2018-9-9 19:27
Seems no people got what is the major I concerned.

Suppose you fly the drone down from a hill.  Could anyone tell me what will be the height of the drone to the ground?

There is no way for the drone to sense it's height above the ground.
You would just have to estimate it.

Nothing like a forum to make a mountain out of a molehill at sea level that is.  

djiuser_PEp4mLwh74c7 Posted at 2018-9-9 19:27
Seems no people got what is the major I concerned.

Suppose you fly the drone down from a hill.  Could anyone tell me what will be the height of the drone to the ground?

The VPS (Visual Positioning System) will give a measure of height to surface directly below aircraft, in the case of the P4P up to a maximum of 10m (33 feet). In theory you could fly down your mountain and use the VPS to be aware of any object below aircraft within 10m. The barometer would continue to show your height relative to take off point. If you fly more than 120m (400 feet) above the surface of the mountain directly below aircraft then you would be breaking the rules in many countries.

Aardvark Posted at 2018-9-10 01:17
The VPS (Visual Positioning System) will give a measure of height to surface directly below aircraft, in the case of the P4P up to a maximum of 10m (33 feet). In theory you could fly down your mountain and use the VPS to be aware of any object below aircraft within 10m. The barometer would continue to show your height relative to take off point. If you fly more than 120m (400 feet) above the surface of the mountain directly below aircraft then you would be breaking the rules in many countries.

Also, VPS may not show the correct altitude if flying above water...

Labroides Posted at 2018-9-9 20:18
There is no way for the drone to sense it's height above the ground.
You would just have to estimate it.

There should be a way to know the current height (what I described in the original post as ACTUAL ALTITUDE).

Aardvark Posted at 2018-9-10 01:17
The VPS (Visual Positioning System) will give a measure of height to surface directly below aircraft, in the case of the P4P up to a maximum of 10m (33 feet). In theory you could fly down your mountain and use the VPS to be aware of any object below aircraft within 10m. The barometer would continue to show your height relative to take off point. If you fly more than 120m (400 feet) above the surface of the mountain directly below aircraft then you would be breaking the rules in many countries.

Return to the post:

Follow the role: if you fly  a drone to a height  of 120m at the hill,  it doesn't against the role.
But If you fly away 4 kilometers down to the hill, the height of the drone to ground is the height of the hill, plus the height of drone to the home pint. Do you think this will be against the role or not?

Antonio76 Posted at 2018-9-10 03:23
Also, VPS may not show the correct altitude if flying above water...

This is the other concern.  Drone always shows minus height.  I really don't know how is the height of the drone above the water.

djiuser_PEp4mLwh74c7 Posted at 2018-9-10 04:57
There should be a way to know the current height (what I described in the original post as ACTUAL ALTITUDE).

There should be a way to know the current height
But there isn't.
It's the same if you were to fly a real plane.
If you flew a small Cessna, you wouldn't have any instruments to tell you how high you are above the ground.
You would have to work it out looking at maps and knowing your height above sea level and doing some thinking and mental arithmetic.

djiuser_PEp4mLwh74c7 Posted at 2018-9-10 05:09
This is the other concern.  Drone always shows minus height.  I really don't know how is the height of the drone above the water.

This is the other concern.  Drone always shows minus height.  I really don't know how is the height of the drone above the water.
When you launch from the pier, you just have to remember how high it is above the water and factor that in to your mental arithmetic.
If it's 10 metres high, don't go below -5 metres etc.

msinger Posted at 2018-9-8 12:03
I mean the altitude shown is always the altitude above the takeoff point. The takeoff point is at 0 feet. Other than when the downward sensors are able to detect the ground below, the drone has no idea how high it is above the ground.

The best answer that is giving the clear understanding that you are talking about. Thank you

Latanzi Posted at 2018-9-8 12:43
I’m curious as to whether the Altitude is measured by the Sensors or by GPS, makes more sense for it to be the latter

The AGL reported in the APP is derived from the Barometer info on the AC

If you want MSL info,  then the GPS Altitude is listed in the EXIF Data in the picture file of A PICTURE taken at a certain location

The EXIF DATA and the Altitude listed on the APP at time of flight are usually 2 different Altitudes unless you are flying from/AT Sea Level.

Randy

rwynant V1 Posted at 2018-9-10 09:17
The AGL reported in the APP is derived from the Barometer info on the AC

If you want MSL info,  then the GPS Altitude is listed in the EXIF Data in the picture file of A PICTURE taken at a certain location

GPS altitude in exif data can be very inaccurate

djiuser_PEp4mLwh74c7 Posted at 2018-9-10 05:09
This is the other concern.  Drone always shows minus height.  I really don't know how is the height of the drone above the water.

Another reason why one is told to fly LOS... If you see your drone you can evaluate its altitude.

Antonio76 Posted at 2018-9-13 04:30
Another reason why one is told to fly LOS... If you see your drone you can evaluate its altitude.

Yes, flying LOS is the best way.

I just feel strange why people cannot understand what was I concern.  

There are kinds of height:
1.  Home point (0) related to drone height;
2. Altitude (based of sea level);
3. The current height of drone related to the ground underneath.

Right now, we only fly with the height one, calculated the home point.
Actually we don't know the exact height of the drone, especially the height of the drone to the ground. However, this is also important to pilot.

Flying the drone within the vision is safeway, but many people more likely fly range.  

djiuser_PEp4mLwh74c7 Posted at 2018-9-13 05:22
Yes, flying LOS is the best way.

I just feel strange why people cannot understand what was I concern.  

I just feel strange why people cannot understand what was I concern.

I think most here are surprised that you were so concerned about something that is obvious and easily dealt with.


Actually we don't know the exact height of the drone, especially the height of the drone to the ground. However, this is also important to pilot.
It's also very easy to work out and understand.
As pilot of  drone you just have to do some of the thinking.
Just like real pilots in real planes.

djiuser_PEp4mLwh74c7 Posted at 2018-9-13 05:22
Yes, flying LOS is the best way.

I just feel strange why people cannot understand what was I concern.  

I think the point is that with the available technology a drone the size of a Phantom -and even bigger- is not likely to be able to carry other types of height/altitude measuring devices (and the related cost is also a big factor... ). Speaking for myself, this is not a problem, I can live with all the limitations  my P4P was born with and I don't ask it to do more than it can safely do.  Others like to stretch the boundaries, and I'm also OK with that, as long as they know what they are doing and do it safely... :-)

msinger Posted at 2018-9-8 08:19
All DJI drones show the altitude above the takeoff point. That altitude shows a negative value when flying below the takeoff point.

If you're flying a drone that has downward sensors (like the Mavic models), DJI GO will show the distance from the drone to ground if the drone is close enough for the downward sensors to detect the ground. If you're flying near the ground, that's the closest thing you're going to get to the current altitude. It's never 100% accurate, but it's acruate enough to determine when you're dangerously close to the ground.

Captain: I appreciate a clearly stated reply. Simply an excellent explanation. Thank you for clear thinking.
Falun

msinger Posted at 2018-9-8 14:16
Yes, it can be difficult to judge the AGL altitude when not flying VLOS.

You're not wrong there !  

Antonio76 Posted at 2018-9-14 03:00
I think the point is that with the available technology a drone the size of a Phantom -and even bigger- is not likely to be able to carry other types of height/altitude measuring devices (and the related cost is also a big factor... ). Speaking for myself, this is not a problem, I can live with all the limitations  my P4P was born with and I don't ask it to do more than it can safely do.  Others like to stretch the boundaries, and I'm also OK with that, as long as they know what they are doing and do it safely... :-)

Well said !  

Labroides Posted at 2018-9-10 05:45
There should be a way to know the current height
But there isn't.
It's the same if you were to fly a real plane.

Too bad we don't get radar altimeters in our drones!  That would make life easier! You are absolutely correct though. Need to be familiar with the charts to know how to calculate your height AGL.

And as he goes "down" hill, once he reaches 400' AGL of the terrain below, he will need to descend to be within regs.

OP, by the look of it there is no way for the drone to detect its actual altitude above sea level. You get the altitude relative to the home point which is considered 0.

I think DJI could make better use of smart phone sensors (E.g. “hey Siri, what’s my current altitude?”) gives you your current altitude above sea level - that could easily be used to set the starting point. If not that, at least it would be nice to allow the user to manually set it.

As for having it accurately update depending on your GPS position, it would be easy for DJI to implement but probably results in liability issues to consider as it would, at best, be an estimate and very likely to fluctuate incorrectly as the landscape dips and dives.

Your best and safest bet is LOS or FPV goggles and a bit of practise to get used to it. Just be prepared to go through a few propellers if you really want to get some macro shots!

twhoffmann Posted at 7-12 01:43
OP, by the look of it there is no way for the drone to detect its actual altitude above sea level. You get the altitude relative to the home point which is considered 0.

I think DJI could make better use of smart phone sensors (E.g. “hey Siri, what’s my current altitude?”) gives you your current altitude above sea level - that could easily be used to set the starting point. If not that, at least it would be nice to allow the user to manually set it.

"I think DJI could make better use of smart phone sensors (E.g. “hey Siri, what’s my current altitude?”) gives you your current altitude above sea level"

Smart phone sensors are no more accurate than the aircraft, and no smart phones have barometer sensing. Any altitude given as a reply by Siri is not going to be accurate either, because the phone has no altimeter and can only give an answer from the GPS which is guaranteed to be quite innacurate.