GPS and drone

[CacheMonkeez]

I attached a Garmin GPS watch to my drone and flew it very high (several hundred feet). After the drone returned, I uploaded the track to Google Earth to see the altitude profile. Google Earth said the drone went only 20 feet high and recorded very little variation in the altitude. I repeated that procedure with my handheld Magellan GPS and got the same result - very little altitude change.

 

Any ideas why my GPS track is not showing the proper altitude?

 

p.s. The GPS tracks that I captured displayed a track and recorded horizontal speeds. It's just the altitude that's note reporting.

Edited June 15, 2015 by CacheMonkeez

[+T.D.M.22]

If I'm not mistaken, it uses pressure to measure height. Just like watches, and airplane altimeter. More pressure equals lower, less pressure equals higher.

 

However, like an airplane altimeter it would have to be reset every liftoff, otherwise it would have no reference to zero (ground level) at that particular location.

 

So, if my guess is right, you'd have to reset/zero the altimeter.

 

If you're really curious you could buy a GPS chip, and altimeter chip. A quick search brought up one from Horizon Hobby for $90. Or you could do your own work and separate components for less money.

[CacheMonkeez]

I'm skeptical about the pressure thing. Anybody else know about this?

[+Team CowboyPapa]

I'm skeptical about the pressure thing. Anybody else know about this?

Well, at one time I did think that I was knowledgeable in that subject matter. Consequently, I did post my opinion. However, another participant characterized my post as sheer nonsense and gibberish:

http://forums.Groundspeak.com/GC/index.php?showtopic=318508&view=findpost&p=5337463

 

I would sure hate to misinform you, so I'll defer at this time.

[CacheMonkeez]

Solved the problem -

 

There is a Google Earth setting when you drop the track log on Google Earth to snap the altitude to the earth's surface. Uncheck that option and it works fine.

[+T.D.M.22]

I'm skeptical about the pressure thing. Anybody else know about this?

Not saying that's how they all work, but some work that way. And the whole airplane altimeter reset is true as well....

[+Red90]

Pressure is the normal way that changes in altitude are measured. It can measure small changes accurately. GPS alititude is much less accurate, but can be used to calibrate the pressure readings due to weather variations. GPS handhelds that include pressure sensors use both together. The third method is radar, but that is quite pricey.

[+ecanderson]

At one time, I thought I had located information regarding the speed at which a Garmin baro sensor would properly update. If I am remembering correctly, there's a fair bit of latency .. nothing you'd see during hiking, but if you ran the drone up and down quickly, there may not have been time to track the pressure changes.

 

Anyone recall where there might be a spec out there for how fast a typical Garmin baro will equilibrate to a given change in altitude?

[+Egnix]

Solved the problem -

 

There is a Google Earth setting when you drop the track log on Google Earth to snap the altitude to the earth's surface. Uncheck that option and it works fine.

 

I don't know if your log has GPS altitude or barometric, but FYI: GPS vertical (altitude) accuracy is much lower than horizontal accuracy. Expect, at best, +/-40ft accuracy for altitude.