Measurement of Angles and Directions Flashcards
(17 cards)
Four Types of Meridians
True Meridian
Magnetic Meridian
Grid Meridian
Assumed Meridian
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.
True Meridian
generally adapted reference line in surveying practice.
True Meridian
passes through the geographic north and south poles of the earth and the observer’s position.
True Meridian
a fixed line of reference which lies parallel with the magnetic lines of force of the earth.
Magnetic Meridian
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.
Assumed Meridian
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 degrees.
The Degree
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 Grad
The circumference of a circle is divided into how many grads
360 degrees = 400 grads
It is commonly used in military operations as in fire direction of artillery units.
The Mil
defined as the angle subtended at the center of
the circle by an arc length exactly equal to the radius of the circle.
The Radian
It is used in computations such as determining the length of circular arcs and where high speed electronic digital computers are used.
The Radian
