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siy12.txt
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SIY12.TXT The Next Step Up 67
Chapter 12
The Next Step Up
The error involved in this surveying method is approximately 1%,
or a precision of 99%. This is due to reading the compass to
only one degree.
If 99% precision is not acceptable, a better compass can be
used. A Brunton pocket transit type compass on a tripod can be
read to a quarter degree. This results in an expected error of
0.45%. The cost of the Brunton Pocket Transit and tripod is
approximately $350.
A Suunto KB-14 compass in a steady hand or on a monopod will
yield about the same results for $100. Unfortunately, the Suunto
only functions on level ground. Also, you cannot use it for a
protractor and ruler to plot your map. There is also a "rivalry
error", introduced by the interaction of the virtual sighting
mechanism and some quirks of human stereoscopic vision.
A staff compass or forester's compass can be read to about a
quarter degree also. The "staff" refers to a Jacob's staff, a
one legged tripod. The cost is about $500. There are several
models.
The next improvement in the instrumentation is a telescopic
compass. These are accurate to about a tenth degree. The
expected error is approximately 0.15%. A telescopic compass and
tripod costs approximately $1000. Several models.
The magnetic field of The Earth is not accurate to a tenth
degree. You will have to be aware of magnetic storms if you try
for this sort of precision with a compass. It is not only
getting expensive, but it is getting to be a lot of trouble too.
This book is supposed to be a poor man's guide to surveying
quickly, easily, and inexpensively.
To obtain errors of less than 0.1%, or a precision of 99.9%,
requires the use of even more expensive and delicate
instrumentation; a transit or theodolite. I never have had any
use for this sort of precision. This is the realm of the civil
engineer. I have never found any land around here worth that
much trouble.
SIY12.TXT The Next Step Up 68
If you have a lot of preliminary surveying to do, an improved
method of measuring distance is available. A small device called
a stringbox will quickly measure distance without an assistant.
A thread is pulled over a rotating counter, and the distance is
read on a dial. These cost about $125.
If you need to read many inclinations, an Abney level is much
handier that the clinometer on the Ranger. An Abney level costs
about $100.
This software package seems to be evolving into three different
products; the present preliminary surveying, simple plotting of
deed descriptions, and 3-D scientific surveying.
I need good examples. Wanna be an example?
Copyright (c)1995 by David Perry Beiter
If you have any questions, problems, or comments, write or call
me.
Dave Beiter, CAVE Inc, 1/2 Fast Road, Ritner KY 42639.
606/376-3137.
byter@mcimail.com
CIS: >MCIMAIL 635-1762