BCRA Grade 5

[Thrun Robert IHMD]

On Thu 16 Jan Wookey said:

>  > My talk in 2000 was the first and only effort to see if
>  > surveys actually met the Grade 5 requirements.
>  
>  I don't think that's true bob. I'm sure there have been 
>  efforts to quantify
>  the accuracy of surveys. For example I have analysed a large 
>  number of CUCC
>  calibration readings to try and understand something about 
>  the errors in a
>  survey. (these are not a real survey 

As you say, these calibration shots are not a real survey.
They give an indication of what can be accomplished under
ideal conditions, but not what was achieved in an actual cave
survey.

>  And Larry Fish has run statistical analysis on large surveys 
>  to see how accurate they really are.

Larry was looking for large errors that indicate blunders.  He 
did try to evaluate accuracy or compare the loop error distribution
to any assumed measurement accuracy.  He has "standard deviation"
as one of the choices of criteria for evaluating loop quality.
I was not able to find any description of exactly how he defines
standard deviation.  If he uses the three-dimensional error 
ellipsoid, it would be a very good way to compare the actual
closures with an assumed standard.  It would be better than the
paper I gave.  I would love to see such a study.

>  People are slightly more discerning than that. They call a 
>  CC&T survey that
>  they took reasonable care over a grade 5 survey. One they 
>  took little care
>  over (or used inferior equipment) they call grade 3, or 
>  maybe 4 if they
>  felt it was somewhere between.

What instruments would you use if you set out to make a Grade 3
survey?  It is obslete except for underwater.

For all practical purposes, Grades 5 and 3 are the same.  Both
are much better than needed for route finding.  Both are good
enough to tell you what valley the cave is headed for or what
area to search for entrances or connections.  Neither is good
enough for drilling a new entrance at the far end of the cave.
The two blend into each other with no clear distinguishing
criteria.  I have seen reports that the Grade 2 survey of Ogof 
Draenen agrees well with the Grade 5 survey.  The difference is
the lack of vertical information in Grade 2.

>  
>  > The revision brings the BCRA Grading
>  > System in line with actual practice and changes the 
>  > System from a failed attempt to quantify the accuracy
>  > to jargon for the sake of jargon.
>  
>  I was generally with you till this last sentence. I do in 
>  fact agree with
>  you that the BCRA grading scheme is not actually very useful for it's
>  intended purpose and a simply serves as a shorthand 
>  description of the
>  method and instruments used. An actual description of the 
>  instruments and
>  method used would probably be rather more useful in 
>  determining expected
>  errors.
>  
>  However this revision does bring things more in line with 
>  practice so I do
>  think that's an improvement, and not just 'jargon for the 
>  sake of jargon'.

I think that Wookey is too accustomed to the BCRA Grading
scheme.  Try telling someone who is not a British caver that
a survey is Grade 5.

   Bob Thrun