BASIC
SURVEYING INSTRUMENTS
Most fieldwork done by an Engineering
Aid (especially at the third- and second-class levels) is likely to consist of
field measurements and/or computations that involve plane surveying of ordinary
precision. This section describes the basic instruments, tools, and other
equipment used for this type of surveying. Other instruments used for more
precise surveys will also be described briefly. Surveying instruments come in
various forms, yet their basic functions are similar; that is, they are all
used for measuring unknown angles and distances and/or for laying off known
angles and distances.
UNIT II -Compass And Plane Table Surveying
MAGNETIC
COMPASS
A magnetic compass is a device
consisting principally of a circular compass card, usually graduated in
degrees, and a magnetic needle, mounted and free to rotate on a pivot located
at the center of the card. The needle, when free from any local attraction
(caused by metal), lines itself up with the local magnetic meridian as a result
of the attraction of the earth'smagnetic North Pole.
Figure
11-3.-Line map made by overlays from the aerial photograph in figure 11-2.
The magnetic compass is the most
commonly used and simplest instrument for measuring directions and angles in
the field. This instrument has a variety of both civilian and military
applications. The LENSATIC COMPASS (available in your Table of Allowance) is
most commonly used for SEABEE compass courses, for map orientation, and for
angle direction during mortar and field artillery fires.
In addition to this type of compass,
there are several others used exclusively for field surveys. The
ENGINEER'STRANSIT COMPASS, located between the standards on the upper plate, is
graduated from 0 o through 360 o for measuring azimuths, and in quadrants of 90 o
for measuring bearings (fig. 11-4). Notice in figure 11-4 that the east and
west markings are reversed. This permits direct reading of the magnetic
direction.
The compass shown in figure 11-5 is
commonly called the BRUNTON POCKET TRANSIT. This instrument is a combination
compass and clinometer. It can be mounted on a light tripod or staff, or it may
be cradled in the palm of the hand.
Other
types of compasses can also be found in some surveying instruments, such as the
theodolite and plane table.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2024 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.