Altitude above sea level during flight

[AZ Desert Eagle]

I understand the height shown on my display while I fly my DJI Mavic 2 drone is from launch point. What I would like to know is if there is a way, while I am flying (not when I download and view on my computer later), to see my actual GPS altitude above sea level. I am trying to replicate the same GPS altitude to retake photos from virtually the same location as before. I can view specific details of exact location and GPS altitude from the properties of the prior photos on my computer, but when I am in the field and flying I seem to only be able to see the elevation above launch point. Does anyone happen to know a way I can see GPS altitude during flight? Thanks for any help.

 

[mavic3usa]

I have no idea how to determine the altitude above sea level while flying the consumer drone, not sure that would be of any value to anyone. Does not the waypoint function suffice to meet your needs?

 

[AZ Desert Eagle]

I do drone aerial photography work related to litigation matters where I am asked to take before and after photos for a project to show the a visual of the impact of the project. So that is why it might be of value to someone. Replicating the view in the after situation requires being able to get the drone to the same location, so knowing the GPS altitude while I am actually flying would be extremely helpful as I can compare it to the GPS altitude of the before photos that I am able to see via Properties. Knowing the elevation above launch doesn't help me all that much to get to same GPS altitude unless I am launching and flying in a super flat location. If the Mavic 2 doesn't have that capability, then so be it. Just hoping someone knows how to view that information while flying.

 

[Meta4]

What I would like to know is if there is a way, while I am flying (not when I download and view on my computer later), to see my actual GPS altitude above sea level.

There is no "GPS altitude" that your drone understands or could calculate.
It only uses GPS for location, not height.

I can view specific details of exact location and GPS altitude from the properties of the prior photos on my computer
, but when I am in the field and flying I seem to only be able to see the elevation above launch point. Does anyone happen to know a way I can see GPS altitude during flight?

You can tell where an image file was captured, but you can't tell it's "GPS altitude".
You can calculate an altitude above sea level if you know the location of the launch point and the relative height when the image was captured.

I do drone aerial photography work related to litigation matters where I am asked to take before and after photos for a project to show the a visual of the impact of the project. So that is why it might be of value to someone. Replicating the view in the after situation requires being able to get the drone to the same location.

Simple .. know the relative height at which the before shot was taken.
Launch from the same place and fly to the same height for your after photos.
If you need to show a height above sea level, just calculate that.

I can compare it to the GPS altitude of the before photos that I am able to see via Properties.

What you think is a "GPS altitude" doesn't come from GPS and is very inaccurate.
Don't even consider using that number for anything.

 

[Prop Wash]

Is there a handheld device that can give you the altitude of the take off point and then can calculate the driver's altitude from your height on the screen? Just asking.

 

[AMann]

Meta4 is correct- consumer grade GPS elevation can vary as much as about +/- 15 meters (50 feet) 95% of the time, and even more the other 5% of the time.

 

[AMann]

Is there a handheld device that can give you the altitude of the take off point and then can calculate the driver's altitude from your height on the screen? Just asking.

An altimeter and a good math brain or calculator. Hand-held altimeters sold for hikers are very accurate as long as you calibrate them often to local air pressure at a known elevation. Then as Meta4 suggested, you just add that to the hight above the takeoff point you see on your screen to get elevation AMSL.

 

[Meta4]

Is there a handheld device that can give you the altitude of the take off point

It's easy to find on Google Earth

 

[AMann]

It's easy to find on Google Earth

That’s cheating! I use my “both hands held” surveying altimeter

 

[Meta4]

Meta4 is correct- consumer grade GPS elevation can vary as much as about +/- 15 meters (50 feet) 95% of the time, and even more the other 5% of the time.

People think that they have a "GPS altitude" when they check the image file properties, but they don't.
DJI give two different heights in the image file metadata, but most simple viewers only show what's in the Exif info and not what's in the XMP section.
The XMP shows the Relative Altitude and Absolute Altitude, Exif only shows something that DJI label as GPS Altitude.
(This is the same height shown as Absolute Altitude in the XMP).

Here's an example of (just some of) the metadata from an image that shows the problem.
It should be obvious that the "GPS Altitude" is junk.

But what DJI call GPS altitude doesn't actually come from GPS and it can be completely wrong by hundreds of feet.
It comes from a faulty calculation that DJI does to come up with a height above sea level from the air pressure.
But the formula doesn't account for normal variation of air pressure due to daily weather.

If you shooting the same feature from the same location on days with different weather and look at the image metadata, it will show completely different "GPS Altitudes" that can vary by large amounts..

To see the relative height from which the image was shot, you need to look in the XMP section of the metadata and need a proper metadata viewer.

If you just click on image properties, you'll just see the completely useless and misleadingly labelled "GPS Altitude".

 

[Yorkshire_Pud]

I am trying to replicate the same GPS altitude to retake photos from virtually the same location as before.

Uum, take off from the same place on successive flights then fly to the same indicated height ?

 

[AZ Desert Eagle]

Thanks for the replies. I didn't realize the GPS altitude data in EXIF was so inaccurate and not really a true GPS altitude. I understand how to calculate and get very close to replicating the exact location and elevation of a shot, but it is a very time consuming and cumbersome process when I have over a 100 photos to replicate, which were taken across a several mile long project, with varying topography and numerous launch points. Having GPS altitude display on my remote controller (apparently just wishful thinking), instead of just height from launch, would greatly reduce the time involved in essentially doing it manually one at a time. It can become even more problematic when your anticipated launch point that you planned for in advance (and used as the basis for calculations) is not available for one reason or another when you arrive, causing you to select another suitable launch point that may be higher or lower. Thanks again for the replies - very informative.

 

[Yorkshire_Pud]

Thanks for the replies. I didn't realize the GPS altitude data in EXIF was so inaccurate and not really a true GPS altitude.

Might a few waypoint flight plans suffice ?
I am not a waypoint person but I think they might do what you need and the Mavic 2/Go4 has a waypoint option, alternatively you could use Litchi.
That said, I do not know if you can stop the drone at a waypoint, take a photo then proceed to the next waypoint or if it simply flies through/via the waypoint and takes a photo whilst passing through the waypoint.
Also, I think that the flight path between waypoints is not a straight line it curves, in 3D, so be careful of ground clearances between waypoints

 

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[PHZ]

I understand the height shown on my display while I fly my DJI Mavic 2 drone is from launch point. What I would like to know is if there is a way, while I am flying (not when I download and view on my computer later), to see my actual GPS altitude above sea level. I am trying to replicate the same GPS altitude to retake photos from virtually the same location as before. I can view specific details of exact location and GPS altitude from the properties of the prior photos on my computer, but when I am in the field and flying I seem to only be able to see the elevation above launch point. Does anyone happen to know a way I can see GPS altitude during flight? Thanks for any help.

I am surprised no one suggested using Litchi to do repeat missions. Maybe I missed something?

That is one of the beauties of the M 2, you can do repetitive missions. Of course, that doesn’t resolve your exact altitude problem, but it solves it to the best degree possible with your drone.

I just finished a year-long project very similar to yours. Every month I shot thirty repeat photos around a construction project using a Litchi mission plan. It is remarkable how close they are to the same position in attitude and altitude. Press a button and wait for it to complete the mission.

 

[mavic3usa]

Does not the waypoint function suffice to meet your needs?

I am surprised no one suggested using Litchi to do repeat missions. Maybe I missed something?

I have litchi but I've never used it on my M2Z since I have found waypoints to be surprisingly accurate and consistent as long as you don't want to do anything fancy.

 

[Droning on and on...]

If you do not need this information in real-time but simply need a record of GPS altitude correlated with when pictures were taken, the automatic flight logs contain this information. They can be extracted after the flight.

 

[AZ Desert Eagle]

I am surprised no one suggested using Litchi to do repeat missions. Maybe I missed something?

That is one of the beauties of the M 2, you can do repetitive missions. Of course, that doesn’t resolve your exact altitude problem, but it solves it to the best degree possible with your drone.

I just finished a year-long project very similar to yours. Every month I shot thirty repeat photos around a construction project using a Litchi mission plan. It is remarkable how close they are to the same position in attitude and altitude. Press a button and wait for it to complete the mission.

That is awesome. I'll have to learn how - sounds like big time saver.

 

[AMann]

If you do not need this information in real-time but simply need a record of GPS altitude correlated with when pictures were taken, the automatic flight logs contain this information. They can be extracted after the flight.

Yeah, but in terms of accuracy and precision, your drone’s GPS altitude data is not very reliable at all (see Meta4’s example above). If you want more accurate results, fly with predetermined waypoints using Litchi or other autonomous flight control programs with AGL settings. They use the in-flight barometer to obtain their altitude (actually their height above the home point from takeoff), which is much more accurate. Then If you want to know the flight altitude or AGL at each photo point, you can easily calculate it using Google Earth to get the ground elevation below the photo and add your pre-determined AGL setting from that waypoint to it.

Edit: I haven’t tried it, but you can also set your waypoints as you fly and shoot and use that for doing real time photo points later on - those waypoints should also accurately use the barometric height above home point data as well (I think…).

 

[Droning on and on...]

Yeah, but in terms of accuracy and precision, your drone’s GPS altitude data is not very reliable at all (see Meta4’s example above).

I didn't see anything in the OP about accuracy. The question was if GPS altitude was available. It is in the logs.

The GPS altitude in DJI drones is as accurate as any other GPS reciever. 10-20m accuracy certainly isn't suitable for landing an aircraft. It may be plenty accurate for locating the point in space where a photo was taken, depending on the application.