The altitude problem.

[solentlife]

Your full flight track is in the flight log. Once imported into a program with a DEM, such as Google Earth - that will show height AGL. Alternatively, if you post photos or video, height AGL can be seen in the EXIF data or simply estimated from the field of view of the camera. So it would be unwise to assume that the FAA or other LE authorities would be unable to verify whether you broke the law.

Question 1 :

Flight track log will show DJI Go / Go4 results for height. Would that not be faulty data as the AC passes over uneven terrain ? It has no Geodetic correctors.

Question 2 : There have been a number of posts here and on DJI forum about large errors in the EXIF data in recordings taken by DJI gear, have you had better results ?

Here's one example thread ..

Altitude information on EXIF

another .... (I know its headache stuff !!)

Wrong altitude data from drone location coordinates

 

[sar104]

Question 1 :

Flight track log will show DJI Go / Go4 results for height. Would that not be faulty data as the AC passes over uneven terrain ? It has no Geodetic correctors.

Question 2 : There have been a number of posts here and on DJI forum about large errors in the EXIF data in recordings taken by DJI gear, have you had better results ?

Here's one example thread ..

Altitude information on EXIF

another .... (I know its headache stuff !!)

Wrong altitude data from drone location coordinates

When the flight data are imported into Google Earth, the (above takeoff location) altitude data are corrected by adding the takeoff elevation and then displayed as absolute (AMSL) altitudes. That correctly displays flight altitude AMSL.

The absolute altitude and GPS altitude fields in the EXIF are generally incorrect because they are actually the same data - the altitude AMSL estimated from ambient pressure assuming a standard atmosphere rather than a known takeoff elevation. That, as you would expect, can give errors of hundreds of meters. That's discussed in more detail here.

It would be much better if they actually used GPS altitude, which is far more accurate. The VDOP is typically approximately 1.5 times HDOP, and so you can expect to be within 5 or 10 meters even without WAAS. I'm in an ongoing dialogue with DJI on fixing that.

 

[solentlife]

Thats interesting about Goggle Earth .... I never knew that .... is that automatically corrected ? I knew that I could get Geodetic height of a location ... but not elevated.

With regard to GPS derived data ... I'll refrain from that arena ... I was involved in trials and usage of Transit and GPS from the old days of Magnavox ... through Trimble to todays commercial and portable military units etc. based on my previous career as a Professional Navigator and being contractor in War Zones. Since then I run various forums and also occasionally give talks on it ....

My questions were purely based on others posts etc. seen around. And that we know the limitation of DJI determination of height.

 

[sar104]

Thats interesting about Goggle Earth .... I never knew that .... is that automatically corrected ? I knew that I could get Geodetic height of a location ... but not elevated.

If the kml file contains altitude data and altitude reference then it will plot the track in 3-D space. Have you not seen 3-D flight track plots in GE?

With regard to GPS derived data ... I'll refrain from that arena ... I was involved in trials and usage of Transit and GPS from the old days of Magnavox ... through Trimble to todays commercial and portable military units etc. based on my previous career as a Professional Navigator and being contractor in War Zones. Since then I run various forums and also occasionally give talks on it ....

My questions were purely based on others posts etc. seen around. And that we know the limitation of DJI determination of height.

I don't understand the point of touting your background in the subject and then declining to discuss it.

 

[solentlife]

If the kml file contains altitude data and altitude reference then it will plot the track in 3-D space. Have you not seen 3-D flight track plots in GE?

No actually ... never had reason to. Interesting - I may give it a whirl ..

I don't understand the point of touting your background in the subject and then declining to discuss it.

No worries ... not touting at all .... just trying to stave off any prod to discuss deeper by illustrating I may know something at least. There is also the fact that some I am not allowed to divulge anyway.
Why I decline ? With the advent of GPS into general life ... car satnavs, quads such DJI ... Yuneec, boating ... smart phones and so on ... a lot of self appointed experts have grown up. I have got tired of being told I don't know about a subject that in fact I have been involved in for many years - in a lot of cases for more years than they've even known about it ...
I think you may understand then that it builds a reluctance to discuss outside of a proper meeting or group. In a face to face meeting or discussion - its easy to solve and conclude, but in forums and internet too often it just becomes a mess. The Internet can be a tough ground ...
Your mentioning GPS Altitude is an example that I gave up trying to get another forums 'expert' to understand ... never again !!
Circle of error Position is another
Averaging
Differential GPS
SA

and on ....

Lets just leave it there I think !! ?

 

[sar104]

No actually ... never had reason to. Interesting - I may give it a whirl ..



No worries ... not touting at all .... just trying to stave off any prod to discuss deeper by illustrating I may know something at least. There is also the fact that some I am not allowed to divulge anyway.
Why I decline ? With the advent of GPS into general life ... car satnavs, quads such DJI ... Yuneec, boating ... smart phones and so on ... a lot of self appointed experts have grown up. I have got tired of being told I don't know about a subject that in fact I have been involved in for many years - in a lot of cases for more years than they've even known about it ...
I think you may understand then that it builds a reluctance to discuss outside of a proper meeting or group. In a face to face meeting or discussion - its easy to solve and conclude, but in forums and internet too often it just becomes a mess. The Internet can be a tough ground ...
Your mentioning GPS Altitude is an example that I gave up trying to get another forums 'expert' to understand ... never again !!
Circle of error Position is another
Averaging
Differential GPS
SA

and on ....

Lets just leave it there I think !! ?

Well that's unfortunate - your insights would likely be valuable. I take the opposite approach - I'm really only comfortable posting on subjects that I do know something about. Being unable to convince everyone just goes with the territory.

 

[skymonkey]

I'm sure that this was discussed already but I just couldn't find it.
Taking off from the hill and ascending to let say 100m. Then you fly at straight line forward away from the hill keeping the same altitude.
But the slope of the hill quickly causes the altitude to become a few 100 m from the ground, although you have still 100m on the display.
How can one keep the drone below those 120m (400ft) if the distance to the ground is not known in such circumstances?

 

[solentlife]

Well that's unfortunate - your insights would likely be valuable. I take the opposite approach - I'm really only comfortable posting on subjects that I do know something about. Being unable to convince everyone just goes with the territory.

As you and many others no doubt observed ... I have 'pet subjects' that I will post on and try to help .... LiPo's being one.
GPS as I am sure you agree - is often grossly misunderstood by many. Trying to educate often leads to grief. I will occasionally 'dip my toes' in a GPS matter but will resist going deeper.

 

[Templin]

Using the Phantom RTK it knows its actual altitude and corrects based on the topography. It is kind of cool, and kind of a PIA.