Module 7 - compass surveying Flashcards
Compass surveying ?
Is the location of points by measuring compass bearings. It is used to find the magnetic north distance.
Compass surveying is recommended (3)
- large are is to be surveyed
- path of a river or coast line is to be surveyed
- area to surveyed is croweded with too much details and triangulation is not possible
Advantages (4)
Some compasses are light and portable
- bearing of can be observed from any point
- mechanism of compass is easy to use
- compass needs less time in setting
Disadvantages (5)
- it is less precise or accurate
- errors may occur because compass was not leveled properly
- distances is not measured by compass
- compass does not reccord elevations
- errors cause by local attractions
Magnetic compasses (2)
Prismatic and surveyors
10 parts of prismatic compass
Mirror
- object valve
- glass cover
- break pin
- compass box
- needle
- graduated ring
- prism
- eye piece
- sun glass
Requirements of magnetic needle?
- it should be sensitive
- magnetic axis should coincide with geometric axis
- end should lie in the same horizontal and pivot point as possible
- stability from center of gravity should be as far below pivot point as possible
- housing box should be non magnetic
What does GN end RB stand for ?
Grid north’s and reduce bearings
Difference between QB and WCB
QB bearing is the system in which the bearing line is measured eastward or westwards from north or south whichever is nearer. WCB is the bearing of a line measured in a clockwise direction from true north towards the line and varies from 0 /360
Difference between TB MB
TB is the horizontal angle between true north and the survey line. It is measured from true north in a clockwise direction. Magnetic bearing is the bearing of a line measeured from the magnetic north.
Difference between TN and MN
TN is the direction of the meridian through a point towards the geographic North Pole of the earth. Magnetic north is the direction in which a freely suspended compasss needle points
