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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 $85. 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 footed tripod. The cost is about $525. 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 $950. 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. There is no 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 between $100 and $200.
If you need to read many inclinations, an Abney level is much
handier that the clinometer on the Ranger. An Abney level costs
between $75 and $150. A Suunto clinometer costs about $90.
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)1994 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.
MCI Mail: 635-1762
byter@mcimail.com
X.400: c=US;a=MCI;s=BEITER;d=id=6351762
CIS: >MCIMAIL 635-1762 (be sure to include your name in the text)