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RE: [Paparazzi-devel] Just an idea on sonar-baro assisted landing.


From: gisela.noci
Subject: RE: [Paparazzi-devel] Just an idea on sonar-baro assisted landing.
Date: Mon, 23 Nov 2009 00:53:23 +0200

As mentioned before, this approach's success lies entirely with the quality
of the sensor; accuracy can be 'nulled' out at that low height AGl when
referenced to the ultrasound sensor, but resolution , repeatability, and
critically, sensor hysteresis need to be sound.

If you are getting good ultrasound ranging 3 meters AGL, then why not use
that sensor all the way down? I use it from 5meters down.
Joe

-----Original Message-----
From: address@hidden
[mailto:address@hidden
] On Behalf Of Chris
Sent: Sunday, November 22, 2009 2:57 PM
To: address@hidden
Subject: [Paparazzi-devel] Just an idea on sonar-baro assisted landing.

I just had a flash and i came up with the following idea:
What if we enable the sonar just to get a good reading by applying very 
strong filtering and data analysis ( say the sonar indicates 3m from 
ground) and then apply this reading to the barometer without taking any 
more sonar readings in to account?
The barometer does not produce noise and it is very accurate for the
descent rate and altitude when the altitude variations are small
and within a short time.
Assuming a barometer with 0.5m (worst case) step accuracy then if the 
sonar positively indicates just once that we are 3 meters from ground 
then we can say:
altitude = 3m - ((baro_pressure_when_3m_were indicated - 
present_pressure) * baro_scale)
Any opinions on this approach?
Chris


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