Backsights (and lava caves)

[Bill Frantz]

At 12:16 AM -0800 1/21/03, Sergey Sorokin wrote:
>The problem with this method, when applied to caves, is that errors in
>defining directions will add while you process with survey. That is if
>you have error of 1 degree at each measurement than you may have error
>of 10 degrees after 10 stations. It is not the problem with 'site'
>survey since in the described situation person get all the readings from
>single position (or may be move but not that much as in cave). So, I
>suppose that in order to get reasonable results it will be required to
>measure angles with quite high precision.


Actually, if you assume that the errors are random, the total error rises
with the square root of the number of stations.  After 10 stations, you
would expect the error to be about 3.2 degrees.  This level of error may be
less than the error introduced by magnetism in the local rocks.

I would think that a practical, tripod mounted, instrument could be read to
1/10 of a degree, perhaps even better.


If you want another hair-brained survey idea, you can do a survey with
nothing but distances.  You need to ensure that there are enough triangles
in your survey to uniquely determine every station relative to the first
station.  I still haven't figured out how to keep book for this technique.
Or how to ensure that you have the triangles you need.

Good Caving - Bill


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