Topic 2: Measurements of Angles and Directions Flashcards
The direction of a line is usually defined by the horizontal angle it makes with a fixed reference line or direction, this is done with reference to a ____
Meridian
DESIGNATION OF NORTH POINTS
True North, Magnetic North, Grid North, Assumed North
Types of MERIDIANS:
True meridian, magnetic meridian, grid meridian, assumed meridian
is the north point of the true meridian. In maps and sketches, it is portrayed in the direction of the actual location of the earth’s north geographic pole and is always shown along a vertical line
True north
a north point that is established by means of a magnetized compass needle when there are no local attractions affecting it. At any point on the earth’s surface its direction is indicated by the direction of the magnetic lines of force passing through the point at a particular time. May be located either east or west of true north
Magnetic north
a north point which is established by lines on a map which are parallel to a selected central meridian. It may
coincide with the lines directed toward true north.
Grid north
is used to portray the location of any arbitrarily chosen north point.
Assumed north
The_____ is defined as the horizontal angle the line makes with an established line of reference. There are
various kinds of angle which can be used to describe the direction of lines. In surveying practice, directions may be defined by means
of: interior angles, deflection angles, angles to the right/left, bearings, and azimuth.
DIRECTION OF LINES
The angles between adjacent lines in a closed polygon are called interior angles. These angles may be measured clockwise
or counterclockwise. It should be remembered that the sum of the interior angles in a closed polygon is equal to (n-2) 180°.
Interior angles
The angle between a line and the prolongation of the preceding line is called a_______. It may be turned to the
right (clockwise) or to the left (counterclockwise) and it is always necessary to append the letters R or L to the numerical
value to define the direction in which the angle has been turned.
Deflection angles
is the acute horizontal angle between the reference meridian and the line. A quadrant system is used
to specify bearings such that a line may fall under one of the following quadrants: NE, SE, NW, and SW. Each quadrant is
numbered from 0° to 90° from either the North or South end of the reference meridian (N-S Line) to the East or West end of
the reference parallel (E-W Line).
Bearings
of a line is its direction as given by the angle between the meridian and the line measured in a clockwise
direction from either the North or South branch of the meridian. ______ are usually preferred over bearings by most
surveyors because they are more convenient to work with such as in computing traverse date by electronic digital
computers. The azimuth of a line may range from 0° to 360° and letters are not required to identify quadrants.
AZIMUTH
can be expressed in different units, all of which are basically derived from the division of the circumference of a circle. A purely arbitrary unit is used to define the value of an angle. The principal systems of units used are:
Magnitude
The sexagesimal system is used in which the circumference of a circle is divided into 360 parts or degrees. The basic unit is the degree, which is further subdivided into 60 minutes, and the minute is subdivided into 60 seconds. The °, and are used to denote degrees, minutes, and
seconds, respectively.
The Degree
is the unit of measure in the centesimal system. In this system the circumference of a circle is divided into 400 parts called ____.
is subdivided into 100 centesimal minutes and a centesimal minute is further subdivided into 100 centesimal seconds. The symbols g, c and
cc are used to denote ___, centesimal minutes, and centesimal seconds, respectively.
The Grad
