Author Topic: Survey Grades  (Read 1694 times)

Offline mulucaver

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Survey Grades
« on: February 28, 2013, 11:02:41 am »
I don't want to get into accuracy or precision as that's already been covered in other posts but I'm interested in other surveyors' views on the grading which should be recorded on the finished map.

The BCRA grading system is related only to the method of surveying and not to the final accuracy so, if I measure to within 1 degree and 1 centimetre I would record a grade 5.

However, when I do the data reduction and I find a loop closure error of say 10%, this certainly means there is either a blunder or a systematic error, which by definition means the survey did not achieve expected accuracy.

Should I therefore downgrade the survey or can I assume that by applying loop error correction the data is now to the expected accuracy?

If the whole survey is a loop then this seems to be acceptable but what if the loop was only a small proportion of the whole survey? If there's an error in the loop one could assume a similar error may be present in the rest of the survey, unless it's a blunder, and this won't be corrected by the software.

With that size of error, of course, you should resurvey that section but that's not always possible on far flung expeditions. Downgrading the survey grade would at least indicate that there may be a problem.
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Offline graham

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Re: Survey Grades
« Reply #1 on: February 28, 2013, 11:50:16 am »
It's can of worms time!!!

If you measure to 0.001 degree and 0.001 mm and get a misclosure  of 0.001% All you know is how precise your measurements have been. You still don't know how accurate your survey is. This is why BCRA grades talk about methods and the precision that comes with those methods. If you don't achieve the necessary degree of precision then you should certainly downgrade the survey

I'll therefore change the subject. ;)

We, in UBSS, are beginning to move over from the BCRA grades to the UIS ones based on a previous system put together by the Australian Speleological Federation (ASF). Details of the system can be found here.

On this system, the forthcoming Gough's Cave survey is graded as UISv1 6-4-BEF The survey of the sumps as far as Sheppard's Crook will be equivalent to UISv1 3-1-B. No grade is claimed for Sump 3.
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Offline peterk

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Re: Survey Grades
« Reply #2 on: February 28, 2013, 02:40:41 pm »
Graham
The document you referred to at http://www.uisic.uis-speleo.org/UISmappingGrades.pdf includes this:

Qualifying suffixes
A nothing has been done to obtain additional certainty of accuracy
B Survey loops are closed and adjusted.
C Survey is dependend on instruments and people which have been checked and corrected for the effects of possible anomalies


The suffix B goes part way towards a solution of the OP's question but in C "people .....corrected....anomalies"!!!!! Lugger, a Dales' surveyor of ill repute had surgery last Friday to make one leg even shorter than the other and this may put his recovery back.

Offline graham

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Re: Survey Grades
« Reply #3 on: February 28, 2013, 03:41:14 pm »
Lugger, a Dales' surveyor of ill repute had surgery last Friday to make one leg even shorter than the other and this may put his recovery back.

I don't think there is anything in the manual about that.  :-\
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Offline John S

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Re: Survey Grades
« Reply #4 on: February 28, 2013, 03:54:11 pm »
I always thought it was a retrograde step when BCRA changed from accuracy to precision.
To answer the question. I would reduce the grade attained but also include the main loops with lengths and % in a small box on the survey [or in the article that would go with the survey]. This way others may see where dubious areas are when looking to joins to other systems etc.
It would be nice to see all major surveys to include such information along with the grade, length, depth, entrance location etc.

Offline graham

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Re: Survey Grades
« Reply #5 on: February 28, 2013, 04:15:24 pm »
I always thought it was a retrograde step when BCRA changed from accuracy to precision.

Trouble is that we have no objective measure of accuracy, whereas we can be reasonably good about precision.

To answer the question. I would reduce the grade attained but also include the main loops with lengths and % in a small box on the survey [or in the article that would go with the survey]. This way others may see where dubious areas are when looking to joins to other systems etc.

I'd like to see more of the article that would go with the survey. very few surveyors have been good at this. Willie Stanton was one who was consistently good at producing these.

It would be nice to see all major surveys to include such information along with the grade, length, depth, entrance location etc.

Time for a plug for the Cave Registry Data Archive.
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Offline graham

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Re: Survey Grades
« Reply #6 on: March 01, 2013, 11:27:12 am »
I'm currently editing an article to go with the survey. In this case, the bulk of the survey was carried out using laser scanning techniques ( no it's not on Mendip).

I'm wondering what grade might be assigned to this.
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