Author Topic: Calibrating a DistoX  (Read 3799 times)

Offline SamT

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Calibrating a DistoX
« on: June 07, 2009, 09:16:51 pm »

Any top tips.

Having done the fiddly bit of soldering it all together, need to do the 2nd fiddly bit of calibration.

Got my head round the instructions - 14 directions (the 6 faces and 8 vertices of a cube) each done 4 times (4 rotary orientations of the distoX).

But this bit about the first 4 being in precise directions. Not quite got my head round it.

I assume the first 4 directions are going to be (lets say) North South East and West. 

Now do these have to be exactly perpendicular directions involving perhaps the drawing of a cross on a board so you can orientate the disto exactly Or are they just saying that for these 4 directions, you have to pick an exact point on which to train the lazer, so that each of the 4 rotatory shots is to exactly the same point.

Thinking of building a tea tray like construction - with a cross in the base - and then points on each 'wall' upon which to train the lazer.
Or is this a waste of time.

Offline Cave_Troll

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Re: Calibrating a DistoX
« Reply #1 on: June 08, 2009, 03:36:04 pm »
Pedant Mode: "Laser" is an acronym. - Light Amplification by Stimulated Emission of Radiation. "L A S E R"

"Lazer" is an American term and presumable refers to - Light Amplification by Zimulated Emission of Radiation

Offline footleg

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Re: Calibrating a DistoX
« Reply #2 on: June 08, 2009, 04:50:45 pm »
Now do these have to be exactly perpendicular directions involving perhaps the drawing of a cross on a board so you can orientate the disto exactly Or are they just saying that for these 4 directions, you have to pick an exact point on which to train the lazer, so that each of the 4 rotatory shots is to exactly the same point.

The second one. In other words, the first four directions just need to be approximately at 90 degrees to each other. There is no need for them to be N,E,S,W. I think it is just that these first four sets of four measurements make a bigger difference in the calibration than the remaining measurements. What is critical however is that all four rotatory shots are from and to exactly the same point.

In practice, you do not need to make anything to do the calibration. Just find a small group of four trees spaced approximately at the four corners of an imaginary square, away from anything metal or electrical. Remember you do not need to keep the Disto on the same station for all the measurements, only for each group of four while rotating the Distox. So if the trees are positioned as follows:

1      2

3      4

You find a spot on tree 1, and measure to a target point on tree 2 approximately level with the spot on tree 1. Use this target for the first four readings, rotating the DistoX between each reading (so take one with the LCD screen facing up, one with it facing left, one with it facing down, and one with it facing right).

Next take 4 readings with the same rotations of the DistoX between trees 1 and 3.
Then do from tree 4 to tree 3, and finally from tree 4 to tree 2. (This order just saves too much walking between trees).

Next you need a set of four readings taken vertically up, then four more taken vertically down. So find a spot with a thick overhanging branch above it for the up shots, and a spot on a branch at eye level to take the down shots to a point on the floor.

You have now taken 24 readings, representing the directions from the centre of an imagined cube to the 6 faces of the cube. Finally we need to take the readings which represent shots from the centre of the cube to the 8 corners (another 32 shots, making a total of 56 calibration readings).
For these, start at tree 1, with the DistoX at eye level, and take four readings to a target point near the base of tree 4.
Next take four readings from near the base of tree 1 to a target point higher up tree 4 (so the clino angle of the shots is around +45 degrees).
Repeat these two sets of four readings from trees 2 to 3, 4 to 1 and finally 3 to 2.

That should give you the total of 56 readings. It takes around 20 minutes to do them in my experience. And a big of practice to get it right.

I realise this is probably a fuller explanation than you were asking for, but thought it might be useful to other people reading the forum.

Offline SamT

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Re: Calibrating a DistoX
« Reply #3 on: June 09, 2009, 11:42:07 am »
right - OK - cheers for that foot leg.

so given that distance is irrelavent.

Could you not do the same in a card board box (with no staples in it!!)

imagine your 1    2

                 3    4

where written in the bottom corners of the box. Then you can just rest the disto on the base of the box.

(just thought though - you'll not be able to press the button when the key pad is face down).

Hmm.

looks like Im off to find some trees tonight then


Offline underground

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Re: Calibrating a DistoX
« Reply #4 on: June 09, 2009, 12:45:55 pm »
Surely 4 garden stakes in the ground at the right place would do the job too... with cross pieces tied on?

Offline sluka

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Re: Calibrating a DistoX
« Reply #5 on: June 09, 2009, 01:46:28 pm »
Surely 4 garden stakes in the ground at the right place would do the job too... with cross pieces tied on?

I'm absolutely sure that only 3 are just enough. ;)

m.

Offline bat

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Re: Calibrating a DistoX
« Reply #6 on: June 09, 2009, 01:51:51 pm »
right - OK - cheers for that foot leg.

so given that distance is irrelavent.

Could you not do the same in a card board box (with no staples in it!!)
imagine your 1    2
                 3    4
where written in the bottom corners of the box. Then you can just rest the disto on the base of the box.
(just thought though - you'll not be able to press the button when the key pad is face down).
Hmm.
looks like Im off to find some trees tonight then


I thought that at first, but it is the line of the laser that is being calibrated and this may not be parallel to the sides of the disto so even with a hole in the box it won't work.
Gary

Offline footleg

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Re: Calibrating a DistoX
« Reply #7 on: June 09, 2009, 01:54:24 pm »
Surely 4 garden stakes in the ground at the right place would do the job too... with cross pieces tied on?

That all depends on how large your garden is! To accurately aim the Disto for each set of four shots, rotating the Disto between each one, it really helps to have the target a good distance away. I found I got my good calibration done when I used trees spaced around 5-10m apart. There are two factors in play here. The first is the precision with which you can place the back end of the Disto on station. The point that should be on station is the spot on the base of the Disto that is in the axis of the laser beam (i.e. where the line of the laser path would come out the back of the Disto if you extended line of the beam backwards from the device). The second factor is the precision with which you position the beam on the target for each shot. Over a longer distance the wobble on the beam is magnified, so it makes you take much more care in holding the Disto steady. If you could position the stakes that far apart then it would be more difficult to see the laser beam spot in daylight, compared to having a wider tree trunk to spot it against. I found it very difficult to see the spot on a sunny day. So overcast, dull or twilight really helps see the spot.

In my case, I could not get far enough from metal objects in my garden to set up 4 stakes any way. What with the metal guttering, washing line post and nails in the fences. And remember you need to take the sets of readings approximating to the corners of the imagined cube, so you stakes need to be as tall as they are spaced apart, or at least as tall as you to take the downward sloping readings as you can't really get much higher and still hold the Disto steady.

That said, I would be interested to hear if anyone manages to get a DistoX calibrated using such an arrangement of stakes.

Offline footleg

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Re: Calibrating a DistoX
« Reply #8 on: June 09, 2009, 01:56:17 pm »

I'm absolutely sure that only 3 are just enough. ;)

m.

I also heard that suggested somewhere, but I cannot work out how you get all the angles you need to represent the 6 faces, and 8 corners of a cube with just 3. Can anyone explain?

Offline sluka

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Re: Calibrating a DistoX
« Reply #9 on: June 09, 2009, 02:13:36 pm »
I'm absolutely sure that only 3 are just enough. ;)
I also heard that suggested somewhere, but I cannot work out how you get all the angles you need to represent the 6 faces, and 8 corners of a cube with just 3. Can anyone explain?

Think about square ABCD: An image a walk around. You should go from A to B, then B to C, then C to D, then D to A. And now omit the point D. You go from A to B and B to C and back from C to B and B to A. The same distance, the same directions. :)

The same it is with calibration of DistoX. The distance between ABC is enough 3-4 m. Because you don't measure from centre, but from B (as centre) to A and to C. From A (as centre) to B and from C (as centre) to B. And somewhere among ABC up to your hand and down between your boots. B. Heeb demonstrated it in Vercors.

"As simple, dear Watson..."


Offline footleg

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Re: Calibrating a DistoX
« Reply #10 on: June 09, 2009, 02:19:25 pm »
But then you need to take the 8 sets of readings to the corners of the cube. You can measure one set of these 45 degree angles from B to C, and another from C to B. But how do you get the others? Or are these not really required to get a good calibration?

Offline sluka

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Re: Calibrating a DistoX
« Reply #11 on: June 09, 2009, 02:27:27 pm »
But then you need to take the 8 sets of readings to the corners of the cube. You can measure one set of these 45 degree angles from B to C, and another from C to B. But how do you get the others? Or are these not really required to get a good calibration?

From A to B and from B to A.

Offline bat

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Re: Calibrating a DistoX
« Reply #12 on: June 09, 2009, 03:36:45 pm »
But then you need to take the 8 sets of readings to the corners of the cube. You can measure one set of these 45 degree angles from B to C, and another from C to B. But how do you get the others? Or are these not really required to get a good calibration?

From A to B and from B to A.

Are you saying  that the 45 degree calibration can be done on the same planes as the horizontal
Gary

Offline SamT

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Re: Calibrating a DistoX
« Reply #13 on: June 09, 2009, 03:38:20 pm »
thats what I read it to mean - but thats not how it reads on the DistoX destructions.

Offline sluka

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Re: Calibrating a DistoX
« Reply #14 on: June 09, 2009, 03:51:47 pm »
thats what I read it to mean - but thats not how it reads on the DistoX destructions.

The first six directions are taken to the middle of the six faces, that
means four of them are horizontal and two are vertical (up and down). The remaining
directions are taken to the 8 vertices of the cube. The precise directions are not important as
long as they are reasonably spread.

To correct a possible error between the Laser and the sensors, a few directed measurements
are needed. Therefore, for the first four directions, the four measurements (display up, right,
down, and left) made in each case are measured precisely in the same direction. This can
easily be done with the horizontal directions, for instance between two trees or cave walls.
In summary, you have to measure 4 precise directions with 4 measurements each and then
another 40 measurements in 10 directions without bearing. The precise number, direction, and
sequence of these remaining measurements is unimportant.
However, it is still recommended
to use a target point and to take some time for each measurement to allow the reading to
stabilize.

Offline footleg

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Re: Calibrating a DistoX
« Reply #15 on: June 09, 2009, 04:01:18 pm »
Very interesting! I've got a DistoX to calibrate this week, so I'll see what happens if I try it using just 3 trees and don't bother trying to get a decent straight up and straight down reading.

Offline SamT

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Re: Calibrating a DistoX
« Reply #16 on: June 09, 2009, 04:02:32 pm »
but we are still saying that the first 4 horizontal directions do have to be precise.
This is the bit I cant get my head round - do they have to be 'precisely' perpendicular. or just roughly perpendicular.

Why has the word 'precise' been used.

Offline sluka

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Re: Calibrating a DistoX
« Reply #17 on: June 09, 2009, 04:07:33 pm »
but we are still saying that the first 4 horizontal directions do have to be precise.
This is the bit I cant get my head round - do they have to be 'precisely' perpendicular. or just roughly perpendicular.

Why has the word 'precise' been used.

... made in each case are measured precisely in the same direction.

Offline biffa

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Re: Calibrating a DistoX
« Reply #18 on: June 09, 2009, 04:21:29 pm »
You should know whether you have taken stuff that is sufficiently orthogonal and whether you have drifted with your aim whilst taking measurements in the 4 different orientations from the calibration quality factor that the software gives you after it has number crunched.  Don't have the manual to hand but it gives you a number in there (0.5 or 0.8?).

I have managed to calibrate one by having sticks with targets on, although I have also done it underground when it is easier.  Absolutely magic to survey with.

Offline footleg

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Re: Calibrating a DistoX
« Reply #19 on: June 09, 2009, 04:32:39 pm »
Sam, the relative directions of the first 4 sets of measurements do not need to be precise with respect to each other. What needs to be precise is the alignment of the laser between the from and to stns within each set of 4 measurements where you barrel roll the Disto.

i.e.
Pick a random direction.

Take 4 precise readings in that direction, rotating the DistoX around it's long axis by 90 degrees (approx!) between each shot. Allow a few seconds with the laser held steady before carefully pressing the button to take the reading for each shot.

How pick another direction roughly 90 degress to the last one used.

Take another 4 precise readings for this new direction, rotating the DistoX about the long axis again between each shot.

Repeat twice more for directions roughly 90 degrees from the last direction again, to complete a total of 16 'precise' readings.

Apparently the remaining readings do not need to be in any particular direction, just well spread. I just try to be precise within each group of 4 readings again.

Offline sluka

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Re: Calibrating a DistoX
« Reply #20 on: June 09, 2009, 04:34:52 pm »
that is sufficiently orthogonal

There is no one one time words "precise orthogonal". The factor is less than 0,5. I received usually less than 0,25.

Offline SamT

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Re: Calibrating a DistoX
« Reply #21 on: June 09, 2009, 04:40:38 pm »

Cool - cheers footleg - got it.

Just wanted to clear up any doubt about 'precise directions' and 'precise repetition' if you like during the barrel roll (nice way of describing it).

Offline sluka

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Re: Calibrating a DistoX
« Reply #22 on: June 09, 2009, 05:04:50 pm »
Thanks footleg for translation. :) Nor for me nor for Beat is the English first language.