SURVEYING (ANGLES PART 1)

ANGLE

defined as the difference in direction between two convergent lines.

ACUTE ANGLE

angle <90 degrees.

RIGHT ANGLE

angle equal to 90 degrees.

OBTUSE ANGLE

angle greater than 90 degrees but less than 180 degrees.

STRAIGHT LINE

angle equal to 180 degrees.

REFLEX ANGLE

angle greater than 180 degrees but less than 360 degrees.

COMPLETE TURN

angle equal to 360 degrees.

HORIZONTAL ANGLE

formed by the directions to two objects in a horizontal plane.

VERTICAL ANGLE

formed by two intersecting lines in a vertical plane, one of these lines is horizontal.

ZENITH ANGLE

the complimentary angle to the vertical angle and is formed by two intersecting lines in a vertical plane, one of these lines directed between the zenith.

SEXAGESIMAL SYSTEM

the circumference of a circle is divided into 360 part or degrees. Basic unit is degree.

CENTESIMAL SYSTEM

the circumference of a circle is subdivided into 400 parts. Basic unit is grad.

THE MIL

the circumference of a circle is divided into 6400 parts. Basic unit is the Mil.

THE RADIAN

sometimes refer to as the natural unit of angle measurement because there is no arbitrary number in its definition.

1 degree is equal to ___ minutes?

60 minutes.

1 minute is equal to ____seconds

60 seconds.

1 degree is equal to ___ seconds

3600 seconds.

1 grad is equal to ___ centesimal minutes

100 centesimal seconds

100 centesimal seconds is equal to ___ cc

10,000 cc

6,400 mils is equal to ____ degrees

360 degrees

1 radian is equal to ___ degrees

180/pi degrees or 57.2958 degrees

1 degree is equal to ___ rad

pi/ 180 degrees or 0.001754522 radians

INTERIOR ANGLES

are measured clockwise or counter-clockwise between two adjacent lines on the inside of a closed polygon figure.

EXTERIOR ANGLES

are measured clockwise or counter-clockwise between two adjacent lines on the outside of a closed polygon figure.

DEFLECTION ANGLE

are measured from an extension of the preceding course and the ahead line. Can be right or left.

DIRECTIONAL ANGLES

formed between a reference line called the meridian line and the line in question. It can bearing or azimuth angle.

MERIDIAN

a fixed line of reference for specifying directions.

ASTRONOMICAL OR TRUE MERIDIAN

• a plane passing through a point on the surface of the earth and containing the earth axis of rotation; determined by the observing the position of the sun or a star.

• are lines of longitude and the converge toward each other at the poles.

MAGNETIC MERIDIAN

• lies parallel with the magnetic lines of force of the earth; the earth acts very much like a bar magnet with a north magnetic pole located considerable south of the north pole defined by the earth’s rotational axis.

• the magnetic pole is not fixed in position but rather changes its position annually.

• do not make good lines of reference.

GRID MERIDIAN

a rectangular XY coordinate system in which one central meridian coincides with a true meridian. all remaining meridians are parallel to this central true meriadian.

ASSUMED MERIDIAN

• an arbitrary direction assigned to some line in the survey from which all lines are referenced.

• this could be a line between two property monuments, the centerline of a tangent piece of roadway, or even the line between two points set for that purpose.

• have no relationship to any other meridian and thus the survey cannot be readily related to other surveys.

BEARING ANGLE

• angle that measures from 0-90 degrees only.

• acute horizontal angle between a reference line and the line in question

• either letter N or S precedes the bearing angle and the letter E or W follows the indicated value of angle.

FORWARD BEARING

the bearing of the line is observed in the direction in which the survey progresses.

BACK BEARING

the bearing of the line is observed in an opposite direction.

AZIMUTHS

• angle that is measured from 0 - 360 degrees.

• the clockwise angle made by the line with the meridian line from either the north or south of the meridian line.

CLOSING THE HORIZON

• process of measuring horizontal angles about a point.

• provides an easy way to test instrument readings if the sum of angles are equal to 360 degrees.

HORIZON MISCLOSURE OR HORIZON CLOSURE OR ANGLE OF CLOSURE

any difference between 360 degrees and the sum of the measured angles.