Altitude reading issue?

[flight-of-eye]

I have done and redone the calibration and IMU reset and still get a reading of 20ft or so when sitting on the ground. I a using my vision to check vineyard drip lines and need to hover a foot or two over the vines . I need to be at six or seven feet however the display is showing 25 to 30ft. If I try and descend to the proper height, BAM, I am in the vine. How does one get an actual reading?

Thanks in advance.

 

[flight-of-eye]

I went out this morning and put her in the air. Did the calibration again, did my dance, and now I am getting a circle pattern at 6ft with a reading of 15ft? On top of that, I am getting serious lag in my FPV. Needless to say, she is grounded for now.

Any insight would be appreciated.

 

[pault]

I do not think you will ever get precise altitude. It would help if the P2V resets it's altitude to zero when it is powered up but I am fairly sure mine doesn't. The barometer will not be that accurate anyway and even if it uses the GPS as well that can give good lateral accuracy but not very good vertically.

 

[jeffwilliams81]

I have owned mine since Christmas, and constantly have a wild altitude reading. Sometimes it will show 40+ feet when it's buzzing next to my head. I wouldn't ever count on that particular reading.

 

[flight-of-eye]

Thank you for the reply. I would hope that there is someone that could lead me in the right direction to search for specific topic titles.

New to the site and not sure of what has been disscused prior.

Thank you.

 

[pault]

There is a link to a custom google search in Shrimpfarmer's signature. Every time I want to search I have to search for one of his posts first - will have to save the link one day

 

[Mossie]

Yes mine always reads about 11 ft when on the ground.

 

[pault]

Yes mine always reads about 11 ft when on the ground.

Similar here, usually always between 10 & 15'. Shame it does not set to zero on power up. It is intriguing to know how it calculates the height. It is obviously relative to your position and not ASL.

 

[dkatz42]

Yes mine always reads about 11 ft when on the ground.

Similar here, usually always between 10 & 15'. Shame it does not set to zero on power up. It is intriguing to know how it calculates the height. It is obviously relative to your position and not ASL.

The control system has a barometric altimeter, which by definition measures air pressure. When the craft starts up, it presumably measures the current value and calls that "0", but there's enough slop so that it won't hold that value for long (thus the 10' or whatever).

Measuring absolute altitude requires barometric compensation--that's why airports always give an altimeter setting (the effective air pressure at sea level; you dial that into your altimeter to make it read *reasonably* accurately).

GPS altimetry is much worse; not only is the geometry of the satellites poor (the ones you really want to receive are blocked by the earth), but the altitude is relative to a model of the earth's shape that is only approximate.

In aviation, things like the minimum altitudes for instrument approaches have enough extra slop built into them so that errors of up to 100' or so won't kill you. I have three altimeters in my plane, and they match to only 50' or so.

The altitude reading should be placarded "for entertainment purposes only".

 

[flight-of-eye]

Yes mine always reads about 11 ft when on the ground.

Similar here, usually always between 10 & 15'. Shame it does not set to zero on power up. It is intriguing to know how it calculates the height. It is obviously relative to your position and not ASL.

The control system has a barometric altimeter, which by definition measures air pressure. When the craft starts up, it presumably measures the current value and calls that "0", but there's enough slop so that it won't hold that value for long (thus the 10' or whatever).

Measuring absolute altitude requires barometric compensation--that's why airports always give an altimeter setting (the effective air pressure at sea level; you dial that into your altimeter to make it read *reasonably* accurately).

GPS altimetry is much worse; not only is the geometry of the satellites poor (the ones you really want to receive are blocked by the earth), but the altitude is relative to a model of the earth's shape that is only approximate.

In aviation, things like the minimum altitudes for instrument approaches have enough extra slop built into them so that errors of up to 100' or so won't kill you. I have three altimeters in my plane, and they match to only 50' or so.

The altitude reading should be placarded "for entertainment purposes only".

Thank you for the information. We look to get a bit of rain in the next few days so as soon as I get a chance I am going to do a degauss of the compass, IMU and compass re-calibration and attempt a flight. I have found a good open field in the country with nothing to interfere and hope I can get this squared out.

 

[FSJ Guy]

In aviation, things like the minimum altitudes for instrument approaches have enough extra slop built into them so that errors of up to 100' or so won't kill you.

That's reassuring! LOL!