Measurement of Angles and Directions Flashcards
The _________________ is usually defined by the horizontal angle it makes with a fixed reference line
or direction.
Direction of a line
sometimes known as the astronomic or geographic meridian.
generally adapted reference line in surveying practice.
passes through the geographic north and south poles of the earth nd the observer’s position.
True meridian
a fixed line of reference which lies parallel with the magnetic lines of
force of the earth.
Its direction is defined by a freely suspended magnetic needle of a compass
held at the observer’s position.
Magnetic meridian
a fixed line of reference parallel to the central meridian of a system of plane rectangular coordinates.
Grid meridian
an arbitrarily chosen fixed line of reference which is taken for convenience.
usually the direction from a survey station to an adjoining station or some
well-defined and permanent point.
Assumed meridian
The sexagesimal system is used in which the circumference of a circle is divided into 360 parts or degrees.
The angle of 1 degree is defined as the angle which requires 1 / 360 of the rotation needed to
obtain one complete revolution.
The degree
the unit of measure in the centesimal system.
The circumference of a circle is divided into 400 parts called grads.
It is divided into 100 centesimal minutes and a centesimal minute is further divided into 100 centesimal seconds.
The Grad
The circumference is divided into 6400 parts called mils, or 1600 mils is equal to 90 degres. It is commonly used in military operations as in fire direction of artillery units.
The Mil
One (1) radian is defined as the angle subtended at the center of the circle by an
arc length exactly equal to the radius of the circle.
It is used in computations such as determining the length of circular arcs and where high speed electronic digital computers are used.
The Radian
