>
>
> I was trying for stereo vision such that the 2D position of the
object was determined by the difference in distance from the two
eyes. Given sufficient separation between the eyes, and given that
they were receiving echoes off the same object, this should have been
possible. However, the inaccuracy beyond about 70cm dwarfed the
occular spacing, rendering the math fairly pointless.
>
Actually, I don't think I would try to do this with SRF0x units. They
have wide beams, and how will you ever know that any 2 echos are from
the same object?
I think you'd do better with some kind of narrow beam device, which
you could pan on a servo, in order to localize objects. Eg, the Sharp
sensors have very narrow beams, and you could correlate the readings
with the sonar distance readings. Also, some of the newer Maxsonars
are supposed to have narrower beams.
I also don't see the point of having 17 echo returns, as IIRC, they
are all from objects at different distances with the SRF0x, and you
seem to want to ID a specific object.
What I would do is mount a couple of different types of sensor,
narrow- and wide-field, on the servo, and pan the array, and then
cross-correlate the results for consistency. I might even use a CdS
cell with a tube on the front to narrow the FOV, as most objects will
have a different reflectance than the background or nearby objects.
If you read Joe Jones' book, Robot Programming, he spends a lot of
time talking about how sensor readings are generally unreliable, and
you need a lot of cross-comparison capability.
>
> I am currently looking at averaging ten readings. The average
stabilized after ten readings such that it is consistent. But I need
to check the standard deviation, as I suspect that I am getting a
tight average with a wide variance. The 10th reading wouldn't do much
to move the average of the other nine, but if the variance is high,
then I still don't really know the location of the item very well.
>
> The reason I liked the SRF08 was that it returned 17 echoes. I only
used the first five or six, but all other sonar sensors gave only a
single echo. The problem with a single echo was that I was intending
to use the identification of items to check my dead reckoning for
location. Since I can't really identify the location of any points,
that isn't possible.
> However, it may still be possible to do that roughly, but I'd have
to average ten readings (or thereabouts) to get a reasonable fix on
an item, and with a wide variance, even that would be dubious.
>
> I'll try a vertical mount to see what that does.
>
>
>
> dan michaels wrote:
> >
> >
> > It's not clear what you mean by "binary pair". Are they
interfering
> > with each other by any chance ???
> >
> > In any case, you might be having problems with sidelobe pickup
with
> > the SRF0x units. I abandoned them myself, and went to the Ping
sonars
> > from Parallax. Other people mentioned the SRF0x units should be
> > mounted "vertically", with the receiver transducer above the
xmtr, so
> > there is nothing for the sidelobes to reflect off of.
> >
> > I found the Ping units work well both close in, and at distances
out
> > to 12' or so. The only problem I did have was using them on a
walker
> > to turn at a wall, and align perpendicularly for moving away from
the
> > wall. When close in [about 6"], and positioned at an oblique
angle to
> > the wall, there appeared to be multiple reflections between the
wall
> > and the bot frame, and which produced spurious readings. However,
> > once the bot was away from the wall 12" or more, the readings
were ok.
> >
> >
> >
>
> --
> View this message in context: http://www.nabble.com/New-range-
finder-needed-tp15923461p15943862.html
> Sent from the OOPic mailing list archive at Nabble.com.
>
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