Disto Calibration Jig

maxf

New member
I am new to cave surveying so this might not be useful what so ever...

Anyway this is what I have been using to make calibrating faster and easier

Its a wooden jig then can be rested in various orientations mimicking the invisible cube required for calibrations.

Lie it flat, stand it up or rest it against a tree for the diagonal shots.

I drilled holes in the wood then hammered in plastic rawl plugs so no metal was used in the construction.

The benefit I see from using this is constant heading and inclination for each shot, no wavering around trying to shoot the same point.

The laser doesn't shoot the same position each time as the reference point of the Disto isn't central to the rear of casing  but as I see it the heading of unit is determined by and invisible line drawn through the centre of the laser and out through the same point on the back of the case parallel to the sides of the instrument so lining the side of the unit up with the wood each time should work (This may be where im going wrong as I have as low as 0.8 so far...)

Here are the pics of it..

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Link to album incase my photo posting doesnt work...

https://flic.kr/s/aHskkod62n


Is this a bad or good idea for Disto calibration ?
 
Good question. How are your error results?

Today I got an error of 0.34 and a max error of 1.05 by using a plastic square and a 2x6 in my back yard. I honestly have no idea whether that is good enough for most people.

11168920_1499972416965766_1571352309496189900_n.jpg
 
A couple things you might consider.

1) The laser actually doesn't matter. Just the orientation. You're using the body of the disto to align things, so you don't really need a stop for the laser beam?
2) I would drill some holes in the 2x4's so that you can reach your finger in and press the trigger button while the disto is face to one of the boards.

I'll leave it at that. I am hoping you'll make an awesome simple jig so I don't have to spend time doing the same :)
 

maxf

New member
caver.adam said:
Good question. How are your error results?

Today I got an error of 0.34 and a max error of 1.05 by using a plastic square and a 2x6 in my back yard. I honestly have no idea whether that is good enough for most people.

11168920_1499972416965766_1571352309496189900_n.jpg

0.8 my the lowest number compared to your 0.34, I can't recall my maximum error.

My plan is to run the calibration again but with the Disto in normal shot taking mode rather than calibration mode (with the cal of 0.8 error loaded up)

I should then see any errors in the heading of the shots and be able to tell how good or bad my calibration was...

 

maxf

New member
caver.adam said:
A couple things you might consider.

1) The laser actually doesn't matter. Just the orientation. You're using the body of the disto to align things, so you don't really need a stop for the laser beam?
2) I would drill some holes in the 2x4's so that you can reach your finger in and press the trigger button while the disto is face to one of the boards.

I'll leave it at that. I am hoping you'll make an awesome simple jig so I don't have to spend time doing the same :)


The wood gives a consistent return each time, rather than just shooting into space and getting error codes..

I could reduce the distance to make it smaller I guess

I used timer count down mode so didn't need a button hole
 

snoboy

Member
[In my limited understanding of how a Disto calibration works,] this actually makes a lot of sense! I like it, and will probably give it a try.

I was under the impression that for the 1st 16 shots of the calibration, the distance is important, as there is some check on the laser alignment also? At least that is how I read the following:
To correct a potential error between the Laser and the sensors, a few directed measurements
are needed. Therefore, for the first four (horizontal) 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 between two points marked for instance on two trees or
cave walls.

Re-reading that I am not so sure it is about distance after all.  :coffee:
 

mulucaver

Member
maxf said:
The laser doesn't shoot the same position each time as the reference point of the Disto isn't central to the rear of casing  but as I see it the heading of unit is determined by and invisible line drawn through the centre of the laser and out through the same point on the back of the case parallel to the sides of the instrument so lining the side of the unit up with the wood each time should work (This may be where im going wrong as I have as low as 0.8 so far...)

The laser beam isn't necessarily in line with the side of the casing or the bottom. I tested mine by holding it against a straight wall and measuring the distance of the centre of the beam from the wall at a point close to the disco and again at the other end of the wall. It was out by maybe 1 degree.
 

maxf

New member
snoboy said:
[In my limited understanding of how a Disto calibration works,] this actually makes a lot of sense! I like it, and will probably give it a try.

I was under the impression that for the 1st 16 shots of the calibration, the distance is important, as there is some check on the laser alignment also? At least that is how I read the following:
To correct a potential error between the Laser and the sensors, a few directed measurements
are needed. Therefore, for the first four (horizontal) 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 between two points marked for instance on two trees or
cave walls.

Re-reading that I am not so sure it is about distance after all.  :coffee:

If it was about distance then i would have hoped a calibration distance might have been recommended.

For example I'm sure it wouldn't be any good if you did the calibration over 1m with the intention if taking shots over 10m if the distance mattered
 
I asked Marco about whether the topodroid calibration equations use distance and this is part of his response:

"calibration uses directions.
distance does not enter the computation.
however bigger distances mean less variation among the "true" directions of the shots of a group.
for example, with a 3cm accuracy on the point of the distox and 3cm accuracy of the target point, over a distance of 2m makes 0.03 angle (ie, about 1.5 degrees). over 4m it is half that, ie, about 0.75 deg."


Sent from my iPhone using Tapatalk
 

maxf

New member
Just as a note, I gave up using my wooden jig and bought a plastic builders square like Adam was using. My calibration value was 0.24.

I surveyed a loop between two entrances (from cave 1 to cave 2 then back to 1), 75m each way and ended up with 0.2m dmsclosure (x 0.18, y 0.08)
 
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