Backsights (and lava caves)

[Sergey Sorokin]

Hello!

Bill Frantz wrote:
> 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. 

Yes, I was speaking about the worst case. In Russia they say "there are
three kinds of lie: lie, insolent lie, and statistics". If you are
speaking about precision than you should add errors. And I was not
speaking that this technique is not practical, I just whant to point out
that it will require more attention to the precision of measurements.

> 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.

You must have at least three legs from each station to get all of them
fixed. If you have a station with 2 legs than it can be located in two
different places (unless it is directly on line between it neighbours),
so you will need some extra data to fix it at the single location.

>  I still haven't figured out how to keep book for this technique.

You should just record distance between stations, where is the problem
here?

> Or how to ensure that you have the triangles you need.

The condition above is neccesary one, I do not know whether it is
sufficient or not (I suspect that this subject was studied long-long
ago, but I just do not know and can't prove it fast).

If we are speaking about the crazy ideas than some sort of hyroscopic
device can be used for this purpose. However some time ago I've read an
article that shows that exiting systems which have sutable
characteristics for cave surveying are too expensive.

WBR,
Sergey.