Lesson 5: Angle and Direction Measurements Flashcards
Components of an Angle
- Reference line
- Direction of the turn
- Magnitude of the angle itself
Angles in the Vertical Plane
- Zenith Angle – angle measured in the
vertical plane - Vertical Angle – angle measured from the
horizontal - Interior Angle
- Deflection Angle
- angle between the line and the prolongation
of the preceding line - Angle to the Right
- measured clockwise from the preceding to the
following line
Fixed line of reference for determining
direction of lines
Meridian
Types of Meridian
- True Meridian
- Magnetic Meridian
- Grid Meridian
- Assumed Meridian
north-south line passing through
the geographic poles of the earth
True Meridian
lies parallel to the magnetic lines of force of the earth and is indicated by the direction of the magnetized needle
Magnetic Meridian
line parallel to the central
true meridian
Grid Meridian
arbitrarily chosen for convenience
Assumed Meridian
Units for Measuring Angles
- Degree
- Grad
- Radians
- Mil
- Sexagesimal system is
used (circumference of a
circle is divided into 360
parts)
The Degree (DMS)
The centesimal system is used (circumference of a circle is divided into 400 parts)
The Grad
is defined as the angle subtended at
the center of a circle by an arc length exactly equal to the radius of the circle
Sometimes referred to as the natural angle
because there is no arbitrary number in its
definition
The Radians
Circumference of circle is divided into 6400
parts
Commonly used in military operations as in
fire direction of artillery units
The Mil
- direction of any line with respect to a given
meridian - indicated by the quadrant in which the line
falls and the acute angle that the line makes
with the meridian in that quadrant
Bearing
Three types of bearing
a. True bearing
b. Magnetic bearing
c. Assumed bearing
- direction as given by the angle between the
meridian & the line measured in a clockwise
direction - on any given survey the direction of zero
azimuth is either always South or always North
Azimuth
Three types of Azimuth
a. True azimuth
b. Magnetic azimuth
c. Assumed azimuth
angle between adjacent lines inside a polygon
Interior Angle
angle between the line and the prolongation
of the preceding line
Deflection Angle
measured clockwise from the preceding to the
following line
Angle to the Right
Instruments for Angle and Direction
Measurement
- Tape
- Magnetic Compass
- Engineer’s Transit
- Theodolite
- Total Station
The angle between the true meridian and
the magnetic meridian
Magnetic Declination
Variations in Magnetic Declination
- Secular Variation
- Annual Variation
- Daily Variation
- Irregular Variation
the magnetic meridian swings in one direction for perhaps 150 yrs until it gradually comes to rest and then swings in the other direction, due to an unexplainable phenomenon
Secular Variation
small annual swing distinct from secular variation; the value is less than a minute
Annual Variation
periodic swing of the magnetic needle occurring
each day
Daily Variation
due to magnetic storms and disturbances caused by solar flares
Irregular Variation
Steps in Closed Compass Traverse Adjustments
- Compute and Adjust interior angles
- Select the best line (line in the
traverse w/c is unaffected by local
attraction) - Adjust observed bearings of
successive lines
