MP exif data in JPEGs: Is altitude meters above sea level?

[hammick]

I was looking at the EXIF data from some of my JPEGS. Assuming the altitude data is correct what exactly is is showing? I am on the latest firmware and 4.15 of the Go 4 App.

It appears to be showing the elevation above sea level for the LAT LONG coordinates and adding in the height of the MP from ground level. I guess I need to take two photos at the same coordinates. One close to ground and another at 400'. Or am I totally off and the MP is giving it's best estimate from it's barometer? I read some threads that DJI started using GPS info a few years back.

Anyone know?

 

[Simmo]

I just checked some jpegs mate and yeah it appears as if its ASL. The elevation has to come from the barometer.
.

 

[Xtreme Drone Pilot]

I just checked some jpegs mate and yeah it appears as if its ASL. The elevation has to come from the barometer.
.

If it is indeed altitude AMSL, not ATOP, it can be quite inaccurate due to chages in sea level pressure due to weather, easily several hundred feet +/-.

 

[hammick]

OK thanks guys. Just so newbies like me can follow along here is what this jargon means.

ASL: Above Sea Level
AMSL: Above Mean Sea Level
ATOP: Above Take Off Point


I will perform some tests tomorrow using my Garmin and the MPP.

 

[hammick]

If it is indeed altitude AMSL, not ATOP, it can be quite inaccurate due to chages in sea level pressure due to weather, easily several hundred feet +/-.

I can assure you the EXIF data is not ATOP unless my MPP is off my 1,600 meters.

 

[Xtreme Drone Pilot]

I can assure you it is not ATOP unless my MPP is off my 1,600 meters.

Then it's most likely AMSL measured by GPS so it's not dependent on weather changes.

 

[hammick]

So I just got done taking some test photos. Took off from the table on my deck which is 12' above the concrete patio below the deck. I set my Garmin Oregon GPS on the table and it was showing elevation of 1,048' which seems accurate for my location in Kansas City. I took a photo with the MP on the table, took off and then landed on the patio and took a photo then took off and took photos at 300' and 400'. My results show the altitude is very inaccurate.

Table: 658' (home point altitude) (390' lower than Garmin indicated elevation)
Patio: 641' (off by 5' from home point)
300': 977' (off by 19' from home point)
400': 1043; (off by -15' from home point)


My patio table has a cast frame and the chairs are also cast so maybe it screws with the barometer. Once it warms up I'll do some more testing taking off from the ground.

 

[GlenT]

So I just got done taking some test photos. Took off from the table on my deck which is 12' above the concrete patio below the deck. I set my Garmin Oregon GPS on the table and it was showing elevation of 1,048' which seems accurate for my location in Kansas City. I took a photo with the MP on the table, took off and then landed on the patio and took a photo then took off and took photos at 300' and 400'. My results show the altitude is very inaccurate.

Table: 658' (home point altitude) (390' lower than Garmin indicated elevation)
Patio: 641' (off by 5' from home point)
300': 977' (off by 19' from home point)
400': 1043; (off by -15' from home point)


My patio table has a cast frame and the chairs are also cast so maybe it screws with the barometer. Once it warms up I'll do some more testing taking off from the ground.

Barometers are not affected by the presence of metallic objects.

 

[okw]

My patio table has a cast frame and the chairs are also cast so maybe it screws with the barometer.

Barometers are not affected by the presence of metallic objects.

And as XDP mentioned above, they are extremely inaccurate for AMSL measurements. Unless they are calibrated quite often, and I've not seen a way to calibrate it in the Mavic.

 

[okw]

I just checked one of my photos from last night. It shows 277.609 and if that is meters, it's within 5 meters of the actual AMSL of the location shown on local topo maps. It's obviously using the GPS altitude measurement.

 

[hammick]

I just checked one of my photos from last night. It shows 277.609 and if that is meters, it's within 5 meters of the actual AMSL of the location shown on local topo maps. It's obviously using the GPS altitude measurement.

So any idea why mine is off by 390' compared to my Garmin?

 

[Cut.Aussie]

You cannot expect accurate height from a GPS, that’s why pilots are not allowed to use GPS fir height only positioning. The way GPS calculates positioning by triangulation of accurate time signals has to great an error for height

 

[hammick]

You cannot expect accurate height from a GPS, that’s why pilots are not allowed to use GPS fir height only positioning. The way GPS calculates positioning by triangulation of accurate time signals has to great an error for height

I understand but off my 390' compared to my Garmin. Seems DJI can do much better.

 

[sar104]

The EXIF data contain two altitude fields in the XMP section: "Absolute Altitude", which is a GPS altitude MSL, and "Relative Altitude", which is barometrically derived relative to the take off point. The value displayed by default by most image processing programs appears to be the absolute altitude value.