Re: [Paparazzi-devel] RE: distance measurement for landing.

[Chris Gough]

On Fri, Nov 13, 2009 at 4:45 PM, gisela.noci <address@hidden> wrote:

Not sure what the link update rate is, and what the link latency is, but these would have to be accurately known. But the system would not would, regardless of these factors, since the closer you came to ground, the less the angular (height) measurement becomes, and the greater the height error becomes for the same latency error, ie, you might work out your height accurately at 100m alt, with lets say 1% error, by vertical triangulation, where 5 degrees error would make a small difference, but at 1meter above ground, a 5degree error would make a huge difference.

 

No go…

OK, so triangulating with zigbee latencies seems like a probable dead end.

I've looked further into scanning phase-beams around 2.4 ghz and there are two big problems; measuring signal strength at those frequencies with any sort of accuracy is expensive, and the beam-forming maths would have to be done in RF, not software as I had imagined, so again difficult/expensive (especially for me, I'm coming into this from a software background).

Is there a reason nobody's suggested differentiating from a second (or more) GPS at a fixed point, i.e. attached to the GCS? Don't surveyors get a few cm accuracy with those sorts of systems?

Chris Gough

 

Joe

 

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From: paparazzi-devel-bounces+gisela.noci=ate-international.com@nongnu.org [mailto:paparazzi-devel-bounces+gisela.noci=ate-international.com@nongnu.org] On Behalf Of Chris Gough
Sent: Friday, November 13, 2009 2:40 AM

To: address@hidden

Subject: Re: [Paparazzi-devel] RE: distance measurement for landing.

 

This might be a silly idea, but...

Is there enough latency information in the zigbee stack to measure the distance between modems? Sure, it's not equivelent to measuring distance from ground, but could you land with it (plus GPS)?

If there was more than one modem at fixed postions on the ground (i.e. different ends of a runway) then to the extent that the atmosphere between the GCS' and the aircraft is the same temp/pressure/humidity, then surely latency will be proportional to distance (?). Since we can know the distance between the modems on the ground, we could turn relative latencies into absolute distances.

With duff-duff, perhaps even suppliment the GPS x/y to get a better z.

Chris Gough.

P.S. with laser + video stream, perhaps the GCS could turn images into a paralax-based distance measure and send them back? Again, I'm not sure about the scale of latencies involved, but I hope a grunty laptop could process the paralax stuff at 30fps (because I'm about to buy one, for learning OpenCV/GpuCV).

https://picoforge.int-evry.fr/cgi-bin/twiki/view/Gpucv/Web/

On Fri, Nov 13, 2009 at 1:51 AM, Sergey Lukin <address@hidden> wrote:

Hi guys,

I'm following this discussion for couple of days and I became curious, aren't there any already existing solutions to the hight measurement problem? I mean budget solutions.

I have found two interesting links:
uwb
http://lea.hamradio.si/~s53mv/radalt/radalt.html
This one will definitely work (this guy made more than 100 safe landings), but requires a lot of knowledge in antena and high frequency devices design.

laser
http://sites.google.com/site/todddanko/home/webcam_laser_ranger
This seems to be much easier. What are the catches to it?

Do you have some more interesting links on this subject? Lets exchange.

Kind regards,

Sergey

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