4 Flashcards
Vertical line
Line follows the direction of gravity (parallel to gravity), called a plumb line
Horizontal plane
A plane perpendicular to the vertical line and intersect to the level surface
Level surface
A curved surface that perpendicular to the vertical line
Mean Sea Level (MSL)
The average height for the surface of the seas
Vertical datum
Kind of level surface where elevations are referenced. Elevation=0
Elevation
Distance along vertical line from vertical datum to an object
Types of datum
Geoid, imaginary sea level surface that undulates over all of the earth
Ellipsoid, simplified model of the earth
Formula:
N = h - H
N: geoid height (from ellipsoid to geoid)
h: ellipsoidal height (from ellipsoid to topography)
H: orthometric height (from geoid to topography)
Leveling? Benchmark? Vertical control?
Leveling, finding elevations of points
Benchmark, permanent object that elevation is known
Vertical control, series of benchmark
Mostly in leveling, an … used to ….
Setting up an optical level in ….. then reading … to measure …
Optical level, read rods
Halfway between the benchmark and target point, tick lines on rod, to measure height
Curvature and Refraction
Curvature, between horizontal plane and level surface. Reading TOO HIGH
deltC = + 0,00785K^2
Refraction, refraction bcs the light rays. Reading TOO LOW
deltR = - 0.011K^2
Total, delth = 0.0675K^2
K=level line distance
How to count elevation leveling
PLEASE REFER TO PPT PAGE 13 14
Delta Elevation measuring method
Taping, to measure depths of mine shafts, floor elevations, etc. example: Electronic distance measurement (EDM)
Barometer, measures air pressure but also affected by circumstances
Levels, in common has three parts: telescope (to create line of sight), internal focusing, system to the line of sight in horizontal plane. We often use dumpy levels, using level vials
Components of dumpy levels
Lens system, gathering incoming light rays and direct them to the reticle plane
Reticle, pair of perpendicular cross hairs
Eyepiece, microscope to see image
Categories of leveling instrument
Automatic levels, consists of prisms suspended from wires to create a pendulum. Automatic will work when bubble is centered.
Digital levels, classified as automatic level but operate with digital image processing. The data will be captured and saved.
Tripods, the adjustable one will be good in rough terrain
Hand level, used for low-precision work to obtain quick checks
Collimation error
The axis of level vial is not parallel to the line of sight. This will not cause errors as long as backsight and foresight distances are balanced.
