Altitude incorrect

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SO I am only about 50 flights in and I have spent it trying to become instinctive on controls and cameras focus. I am getting ready to head out to a big off road event and I want to use follow me but I am worried about the altitude. I took a shot of it saying it was at 32 feet up yet it is clearly only 6 feet off the ground.
 

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SO I am only about 50 flights in and I have spent it trying to become instinctive on controls and cameras focus. I am getting ready to head out to a big off road event and I want to use follow me but I am worried about the altitude. I took a shot of it saying it was at 32 feet up yet it is clearly only 6 feet off the ground.
Yep- that's wrong! I don't know if a compass or level calibration would help (if you haven't done so already).

I would just call 3DR tech support and ask them. They are really good over the phone and are there 24/7.

If nobody else posts a solution, let us know what you find out.
 
The altitude reported comes from the barometer inside Solo. Many factors can make the altitude reported be off. Weather, being close to the ground with prop wash, etc. will make the barometer less accurate.
 
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The altitude reported comes from the barometer inside Solo. Many factors can make the altitude reported be off. Weather, being close to the ground with prop wash, etc. will make the barometer less accurate.
Good point- you can't adjust the barometer in Solo like you can a plane to compensate for barometric pressure changes.
 
SO I am only about 50 flights in and I have spent it trying to become instinctive on controls and cameras focus. I am getting ready to head out to a big off road event and I want to use follow me but I am worried about the altitude. I took a shot of it saying it was at 32 feet up yet it is clearly only 6 feet off the ground.
The issue is probably not one of atmospheric pressure.

You say you is was at 6 ft and you are reading 32. That different - 26 ft - represents about -12 psi difference. And no way can the local pressure be that much at otherwise you might be gasping for air!
 
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On earth, at least, a 26' difference in elevation will produce about a 0.01psi change in air pressure. If you're gasping for air in a 3rd story building, David8477, I can only assume your office building is on Jupiter?
 
On earth, at least, a 26' difference in elevation will produce about a 0.01psi change in air pressure. If you're gasping for air in a 3rd story building, David8477, I can only assume your office building is on Jupiter?
You are absolutely correct! I was thinking of water depth and pressure.

Brain fart!
 
The SOLO has a barometric altimeter and also obtains altitude data from GPS. At initialization it knows it is on the ground and associates the pressure reading with 0 AGL thus knocking out the effects of weather, in particular the barometer reading and temperature). I expect it also looks at the GPS reading (height above ellipse or height above geoid) and takes out the bias. It thus has two ground level references. In the short duration of a flight neither the weather nor the GPS constellation should change that much and both measurements should read pretty close to AGL 0 upon return to the launch point. Which they display and which they use to determine to slow down the rate of descent I really don't know but I suspect its the barometer because of they thought GPS was good enough they wouldn't have installed the barometer. Indeed GPS is notoriously bad in altitude measurement because there are no visible satellites below you.

What really upsets the apple cart is if you walk up or down hill and try to land there. The altitude display will be way off as 0 is the level at which you calibrated. On top of a 50 ft hill 60 ft as displayed is really 10' AGL.
 
Good point- you can't adjust the barometer in Solo like you can a plane to compensate for barometric pressure changes.

Yes, you can and that's what SOLO doubtless does though in an airplane one subtracts QNH (what's dialed into the Kollsman window) such that the altimeter reads the field elevation if one is at the field at which QNH was measured (QNH is found by turning the Kollsman knob until the altimeter reads the field elevation and broadcasting what is dialed in) but with the SOLO one subtracts QFE from the barometer reading (found by turning the Kollsman knob until the altimeter reads 0) and then takes off. QNH gives height above mean sea level as long as the barometer reading is the same as your location. QFE gives height above ground as long as ground height is the same height as the height at which you set the barometer and the barometer didn't change.
 
The SOLO has a barometric altimeter and also obtains altitude data from GPS. At initialization it knows it is on the ground and associates the pressure reading with 0 AGL thus knocking out the effects of weather, in particular the barometer reading and temperature). I expect it also looks at the GPS reading (height above ellipse or height above geoid) and takes out the bias. It thus has two ground level references. In the short duration of a flight neither the weather nor the GPS constellation should change that much and both measurements should read pretty close to AGL 0 upon return to the launch point. Which they display and which they use to determine to slow down the rate of descent I really don't know but I suspect its the barometer because of they thought GPS was good enough they wouldn't have installed the barometer. Indeed GPS is notoriously bad in altitude measurement because there are no visible satellites below you.

What really upsets the apple cart is if you walk up or down hill and try to land there. The altitude display will be way off as 0 is the level at which you calibrated. On top of a 50 ft hill 60 ft as displayed is really 10' AGL.
GPS altitude is not used in relation to Solo. And with consumer GPS altitude accuracy of 8-10 x horizontal, I'm glad they don't.
 
No ones asked yet, so just to double check the obvious.... Altitude is measured from the take off location, so did you happen to arm and takeoff in a different location? Perhaps down the street or in the back yard.

If YES, then it is possible your Solo was 32 feet above the takeoff location, though only 6 feet above the road where you took the picture.

If NO then you better keep an eye on that. It could just be a one off, but if not that's likely going to require a replacement Solo because you can't swap out the barometer yourself.

The barometers on all these drones are very sensitive to moisture. If it was very humid, or if it was cold, that could cause issues with the barometer. For example, for winter flying it's best to let the Solo (or any drone) sit out in the cold to acclimate for at least 15 minutes. Bringing it from a warm house or car out into the cold and starting right up can cause condensation in the barometer. I leave mine in the car or garage overnight and only keep the batteries warm.
 
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GPS altitude is not used in relation to Solo. And with consumer GPS altitude accuracy of 8-10 x horizontal, I'm glad they don't.
It's worse but not nearly that much worse. More like twice and a bit. Example: 10 satellites randomly dispersed over the 12 hr sphere have an average HDOP of 0.97 and a VDOP of 2.1
 
It's worse but not nearly that much worse. More like twice and a bit. Example: 10 satellites randomly dispersed over the 12 hr sphere have an average HDOP of 0.97 and a VDOP of 2.1
I know it can vary greatly and is why it is not used. Posted a couple weeks ago by Garmin..
« Get additional answers from Garmin

How accurate is the GPS elevation reading
01/07/2016

GPS heights are based on an ellipsoid (a mathematical representation of the earth's shape), while USGS map elevations are based on a vertical datum tied to the geoid (or what is commonly called mean sea level). Basically, these are two different systems, although they have a relationship that has been modeled.

The main source of error has to do with the arrangement of the satellite configurations during fix determinations. The earth blocks out satellites needed to get a good quality vertical measurement. Once the vertical datum is taken into account, the accuracy permitted by geometry considerations remains less than that of horizontal positions. It is not uncommon for satellite heights to be off from map elevations by +/- 400 ft. Use these values with caution when navigating.
 
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No ones asked yet, so just to double check the obvious.... Altitude is measured from the take off location, so did you happen to arm and takeoff in a different location? Perhaps down the street or in the back yard.

If YES, then it is possible your Solo was 32 feet above the takeoff location, though only 6 feet above the road where you took the picture.

If NO then you better keep an eye on that. It could just be a one off, but if not that's likely going to require a replacement Solo because you can't swap out the barometer yourself.

The barometers on all these drones are very sensitive to moisture. If it was very humid, or if it was cold, that could cause issues with the barometer. For example, for winter flying it's best to let the Solo (or any drone) sit out in the cold to acclimate for at least 15 minutes. Bringing it from a warm house or car out into the cold and starting right up can cause condensation in the barometer. I leave mine in the car or garage overnight and only keep the batteries warm.


So this is every time i take her up to 400 foot altitude cap. I like to fly up high so i can maintain sight of the drone. but it seems everytime I land as I try to precisely land at same spot manually. I have never seen it be within 15 feet of ground level when landing. I am always landing in my driveway from the same spot. Has anyone used follow me with fairly low level flights
 
What Garmin says is perfectly consistent with what I said. Garmin should understand this. They have been in the business a long time. The first paragraph is irrelevant here. The receiver computes position in WGS 84 cartesian coordinates, transforms those to the ellipsoid and, finally, if desired to the geoid or at least calculates and reports the geoid - eliipsoid difference which is based on location based interpolation between carefully surveyed benchmark points. The reason it is irrelevant is because the first altitude reading (at startup) will be subtracted from all subsequent readings. As an example I read the following altitudes from my iPhone (indoors - it's cold out there today - but next to a window), at 1 minute intervals 270,273, 273, 271, 272, 271, 270, 267, 268, 267, 267, 267, 273, 276, 277, 279. The actual altitude of the phone was 290.8 ' so all those numbers are in error. Were I the SOLO I'd subtract the first reading from each and obtain AGL altitude estimates of 0, 3, 3, 1, 2, 1, 0, -3, 2, -3, -3, -3, 3, 6, 7 and 9 feet. Those really aren't too bad and certainly good enough to assist in checking on the barometer or even use in a pinch if the barometer failed in flight. If I were the systems engineer that's what I'd do. Note that this is exactly what is done with the barometric data. The bias from the fact that SOLO is not at sea level on a standard day are removed by subtracting the altitude measured at initialization from each subsequent altitude reading.

The reason that this works is that the constellation does not change much over the course of a 15 minute solo flight so GDOP doesn't either and, unless a satellite is rising or setting, the estimated height AGL isn't going to either. Note further that SOLO can obtain GDOP, or it's component, VDOP from the GPS module. It can probably also obtain the covariance matrix of the satellite psuedo range residuals or at least the residuals vector from which it can determine the uncertainty in the altitude measurement and thus decide what weight to give the GPS altitude data. This is not to say that SOLO does or does not use GPS altitude as I have no clue as to how the thing is engineered. But I do know that engineers really hate to throw away data.

My iPhone said that the uncertainty in altitude was from 10 - 13' over that. I don't know whether that is one sigma or 2 or whatever. The standard deviation in those altitude data is 3.8 ft.
 
So this is every time i take her up to 400 foot altitude cap. I like to fly up high so i can maintain sight of the drone. but it seems everytime I land as I try to precisely land at same spot manually. I have never seen it be within 15 feet of ground level when landing. I am always landing in my driveway from the same spot. Has anyone used follow me with fairly low level flights
Ok. So that eliminates the obvious (your not taking off from lower ground). I would use the Solo app to put a support ticket into 3DR (including the logs). Ask them to check your barometers.

I have done low altitude follow me missions. The drone will stay at the same altitude relative to its takeoff point. So if you have it following you at 15 feet, and you drive up and over a 30 foot hill, the Solo will crash into the hill. It does not follow the contours of the terrain.
 
What Garmin says is perfectly consistent with what I said. Garmin should understand this. They have been in the business a long time. The first paragraph is irrelevant here. The receiver computes position in WGS 84 cartesian coordinates, transforms those to the ellipsoid and, finally, if desired to the geoid or at least calculates and reports the geoid - eliipsoid difference which is based on location based interpolation between carefully surveyed benchmark points. The reason it is irrelevant is because the first altitude reading (at startup) will be subtracted from all subsequent readings. As an example I read the following altitudes from my iPhone (indoors - it's cold out there today - but next to a window), at 1 minute intervals 270,273, 273, 271, 272, 271, 270, 267, 268, 267, 267, 267, 273, 276, 277, 279. The actual altitude of the phone was 290.8 ' so all those numbers are in error. Were I the SOLO I'd subtract the first reading from each and obtain AGL altitude estimates of 0, 3, 3, 1, 2, 1, 0, -3, 2, -3, -3, -3, 3, 6, 7 and 9 feet. Those really aren't too bad and certainly good enough to assist in checking on the barometer or even use in a pinch if the barometer failed in flight. If I were the systems engineer that's what I'd do. Note that this is exactly what is done with the barometric data. The bias from the fact that SOLO is not at sea level on a standard day are removed by subtracting the altitude measured at initialization from each subsequent altitude reading.

The reason that this works is that the constellation does not change much over the course of a 15 minute solo flight so GDOP doesn't either and, unless a satellite is rising or setting, the estimated height AGL isn't going to either. Note further that SOLO can obtain GDOP, or it's component, VDOP from the GPS module. It can probably also obtain the covariance matrix of the satellite psuedo range residuals or at least the residuals vector from which it can determine the uncertainty in the altitude measurement and thus decide what weight to give the GPS altitude data. This is not to say that SOLO does or does not use GPS altitude as I have no clue as to how the thing is engineered. But I do know that engineers really hate to throw away data.

My iPhone said that the uncertainty in altitude was from 10 - 13' over that. I don't know whether that is one sigma or 2 or whatever. The standard deviation in those altitude data is 3.8 ft.
The Solo doesn't use GPS for altitude. That is known. The reason is because of poor accuracy. At least that's what the developers have openly discussed on diydrones and github. While everything you have said is no doubt true, I think there might be a difference between what "should" be possible in theory versus what actually works in the field. I don't know. I do know that GPS on the Solo (and any drone) is far less accurate near the ground unless you are in a very open area. It would seem unwise to use any data from the GPS, even as a sanity check, when you can put 2 or 3 barometers on a drone.
 
So this is every time i take her up to 400 foot altitude cap. I like to fly up high so i can maintain sight of the drone. but it seems everytime I land as I try to precisely land at same spot manually. I have never seen it be within 15 feet of ground level when landing. I am always landing in my driveway from the same spot. Has anyone used follow me with fairly low level flights

You can't expect too much of a barometric altimeter. If you were to go out and spend as much on an electronic altimeter as you spent on your SOLO (with gimbal) you could expect accuracy of ± 0.4 mB. That corresponds to a 3.3 m (10.8 ft) uncertainty in altitude. Now we would assume that over 15 minutes such a barometer wouldn't drift much but looking back over some data from one of these (Honeywell Precision Barometer) I see variation of 0.2 mB over 15 minutes corresponding to 1.65 m (5.4 ft). Assuming that whatever SOLO has isn't as accurate as an HPB maybe GPS assisted barometry doesn't seem so far fetched!
 
You can't expect too much of a barometric altimeter. If you were to go out and spend as much on an electronic altimeter as you spent on your SOLO (with gimbal) you could expect accuracy of ± 0.4 mB. That corresponds to a 3.3 m (10.8 ft) uncertainty in altitude. Now we would assume that over 15 minutes such a barometer wouldn't drift much but looking back over some data from one of these (Honeywell Precision Barometer) I see variation of 0.2 mB over 15 minutes corresponding to 1.65 m (5.4 ft). Assuming that whatever SOLO has isn't as accurate as an HPB maybe GPS assisted barometry doesn't seem so far fetched!
So now your just trolling right? Barometers are much more accurate for measuring relative changes in altitude.
 
You can't expect too much of a barometric altimeter. If you were to go out and spend as much on an electronic altimeter as you spent on your SOLO (with gimbal) you could expect accuracy of ± 0.4 mB. That corresponds to a 3.3 m (10.8 ft) uncertainty in altitude. Now we would assume that over 15 minutes such a barometer wouldn't drift much but looking back over some data from one of these (Honeywell Precision Barometer) I see variation of 0.2 mB over 15 minutes corresponding to 1.65 m (5.4 ft). Assuming that whatever SOLO has isn't as accurate as an HPB maybe GPS assisted barometry doesn't seem so far fetched!
In spite of all the technical jargon above, I was agreeing with you. And the point remains that GPS alt is not used in the Solo and for all of the above reasons you stated. When you are dealing with AGL altitudes of less than 400' and consumer grade GPS receivers, there is simply no place for it. As far as barometers failing, that's why there are 2 in the Solo.
 

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