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PICList Thread
'Forest Ranger'
1997\11\13@032048 by Anton Schoultz

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Greetings fellow PICsters!

I have been following the SSU thread with great interest. I have seen some unique sugestions on 'how to do sonic ranging'. I am would like to know what ingenious methods you guys & gals can come up with for the following:-

Background:
My brother-in-law works for Mondi (Forestry, Paper Mills etc). Part of his work involves doing calculations on timber yeilds etc., for reasons best left to the forestry people, they take a 'sample area' in the forest of a circular area of radius 7.5 meters.

Requirements:
Portable device(s) preferably hand held, which can guage a distance of 7.5 meters. indicators of 'too close','too far' & 'just right' would do the trick.

As trees are counted as in/out of the circle, I would imagine that a measurement within say 5cm to 10cm of the nominal 7.5m would suffice.
ie
5cm 745cm-755cm=OK  <745cm=too close  >755cm=too far.
10cm 750cm-760cm=OK  <750cm=too close  >760cm=far

My initial thought was to have two units,
1)the center of the circular sample area,
2)hand-held (PIC based) unit with LED indicators for "Too close","Too far" & "OK"

My idea was to combine radio & ultrasonic thus-
Handheld - button "Measure" transmits a radio signal to the center unit, which upon receiving the radio signal, responds by sending out an ultrasonic signal, bounced off a conical disperser. The hand-held would then time how long it took to detect the ultrasonic sound.
For the distance involved, I am assuming negligable delay on the radio wave (at speed of c - a fair assumtion me thinks!)so the time, after allowing for cct delay at center, would be a measure of the distance. I opted for one-way ultrasonic in the hope of acheiving the range required in the wooded forest. Bounced signals could be a problem, time first detection, ignore rest. (sortes time would be sortest distance - hopefully straight line!)

The hand-held could also have a "calibrate" button, the idea being that at the start of the measuring session, the units are placed 7.5m apart (by tape measure!) and the calibrate is pressed. The unit then measures the time, and stores it. This stored time is then used for comparison for the close/ok/far times. Calibration just prior to the measurements arround the circumference would, I believe, compensate for temperature, humidity and other environmental variants; all of which are likely to stay more-or-less constant for the period of measurements. Could be re-calibrated for each sample as the day progresses. (Eastern Tvl/Umpumalaga is cool in the am with occasional mist, and pretty hot & dry in the afternoon!)

At present these measurements are done with EXPENSIVE optical devices such as surveyers use. - Striped pole & peep box :-) so line of sight (albeit blurred!) may be assumed.

Anyone have any bright and alternate solutions?

Many thanks in advance
Anton Schoultz

1997\11\13@104312 by Rick Dickinson

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At 10:19 AM 11/13/97 +0200, Anton Schoultz wrote:
>Greetings fellow PICsters!
>
>I have been following the SSU thread with great interest. I have seen some
unique sugestions on 'how to do sonic ranging'. I am would like to know what
ingenious methods you guys & gals can come up with for the following:-
>
>Background:
>My brother-in-law works for Mondi (Forestry, Paper Mills etc). Part of his work
involves doing calculations on timber yeilds etc., for reasons best left to the
forestry people, they take a 'sample area' in the forest of a circular area of
radius 7.5 meters.
>
>Requirements:
>Portable device(s) preferably hand held, which can guage a distance of 7.5
meters. indicators of 'too close','too far' & 'just right' would do the trick.
>
>As trees are counted as in/out of the circle, I would imagine that a
measurement within say 5cm to 10cm of the nominal 7.5m would suffice.
>ie
> 5cm 745cm-755cm=OK  <745cm=too close  >755cm=too far.
>10cm 750cm-760cm=OK  <750cm=too close  >760cm=far

[snip]

>At present these measurements are done with EXPENSIVE optical devices such as
surveyers use. - Striped pole & peep box :-) so line of sight (albeit blurred!)
may be assumed.
>
>Anyone have any bright and alternate solutions?

Has anyone given any thought to the ultimate "low-tech" solution?

Attach a piece of light chain (like used for dogs) to the top of a metal pole
which is hammered into the ground.  Or, actually use one of those dog chains
which comes attached to a corkscrew-like metal stake which you twist into the
ground.  Have several links painted flourescent orange or green in the band
between 740cm-760cm from the pole.  Pull it tight next to the tree, and make
your judgement.

Much cheaper than surveying equipment, and simpler than an ultrasonic method.

What do you think?

- Rick "K.I.S.S." Dickinson

---
You can help design a Serial Sonar Unit for model robots!
 Vist http://www.notesguy.com/notesguy for details, or
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