Horizontal Angle
The angle between two directions measured in a horizontal plane, a fundamental element in geodetic measurements.
A horizontal angle is the angle between two directions measured in a horizontal plane. It is one of the fundamental elements in geodetic measurements and is used to determine the relative position of points.
Types of horizontal angles:
- Direction angle - angle from north to a specific direction (azimuth)
- Deflection angle - angle between two adjacent directions
- Interior angle - angle inside a polygon
- Exterior angle - angle outside a polygon
Angle measurement methods:
Horizontal angles are measured with a theodolite or total station using various methods:
- Repetition method - angle is measured multiple times and average is calculated
- Direction method - all directions from one point are determined and angles calculated
- Polar method - combines angle and distance measurements
Horizontal angle precision:
Modern electronic total stations provide horizontal angle measurement with precision up to 0.5 seconds (approximately 0.00015 degrees). High-precision instruments achieve even 0.1 second precision.
Application in surveying:
- Boundary determination - angles between boundary points
- Construction stakeout - determining structure placement
- Traverse surveying - densification of geodetic network
- Detail surveys - fixing object positions
Error sources:
Horizontal angle measurements must account for possible errors: instrument centering error, target sighting error, atmospheric effects, and mechanical imperfections of the instrument. Professional surveyors use special methods to minimize these errors.