Understanding DIN specs

scott-zelenak · 2010-11-01T22:44:02Z

Occaisionally, I have the 'opportunity' to explain these standards to other surveyors. I often ask other surveyors what their "confidence level" is in their results. The answer of "110 %" is guaranteed to elicit giggles. There are some pretty common misconceptions involving the expected precision of an angle turning. Even I misunderstood some of the concepts, so I have tried to condense and codify what I think I know.It is quite a few years since I have had the chance to read the DIN specs and I have only briefly had an encounter with the new ISO specs. Terminology is quite important in the specs and is not interchangeable; one of the commonest errors made in these discussions.Hopefully, I will get this right...A pointing is one sighting of one target. Two pointings, one at the BS and one at the FS is a direction. Two directions, one in each face, is an angle. Two angles is a set or one repetition.The DIN 18723 spec is not the accuracy of an angle. It is the uncertainty in pointing face direct and pointing face reverse at one target. This standard deviation is merely an expression of precision.In order to apply the DIN spec to an angle one has to multiply the standard deviation by 2 then divide by the square root of the number of directions. One must also remember that these results represent the standard deviation of 68 % confidence. In order to estimate the values of 95 % or 99.9 % confidence the appropriate multipliers are required.These values then equate to optimal procedures, equipment and conditions. Poor pointing techniques, weak tripods, and sun shimmer quickly degrade results. For example, pointing to the apparent prism center rather than a manufacturer provided target can cause “prism confusion”, where the center of the apparent prism is, in effect, a mirage, displaced due to poor alignment of the prism to the instrument. Only after systematic biases are understood and compensated for might possibly standard deviation be a representation of accuracy.The new ISO 12857 Part 2 standard created a new means of determining Theodolite accuracy. A test series of 5 targets spaced around the horizon evenly at distances from 100 to 250 meters are observed in four series of observations. Each observation comprises three sets of directions to each target. A least squares adjustment then determines the experimental standard deviation of a direction observed in both faces.This standard has been revised and replaced by ISO 17123-3:2001 (which I have not had the pleasure to view).In order to keep all this straight I made an excel sheet;I have made an honest attempt at correctness here, so, of course, if somehow I have misspoken I am assured someone will kindly correct me. One note, the math is done by the excel sheet, so...

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Jim Frame, post: 441947, member: 10 wrote: That's the way I use the term (almost -- I use BSD, BSR, FSD, FSR), regardless of what DIN or anyone else says. And for most boundary work I only turn 1 set.

That's the way I do it. But, with a total station instrument, in some circumstances (like if you have only one rod/glass combo for sighting) it might be convenient to do it BF,BR, FR, FD - and it wouldn't make much, if any, difference to the results.

Posted : August 13, 2017 9:48 pm

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Understanding DIN specs

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