Lab2 Lecture2 Leveling

8/20/2019 Lab2 Lecture2 Leveling

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! Design of highways, railroads, canals, etc.

! Layout construction projects according to specific design

! Calculate earthwork volumes

! Investigate drainage characteristics

! Develop maps showing general ground configurations

! Monitor earth subsidence

Leveling-Theory and Methods

Leveling is the process by which elevations of points or

differences in elevation are determined.

Areas of Application


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curved surface that at

every point is perpendicular to the

direction of gravity

(plumb line), e.g. still

lake surface.

A level surface to

which elevations

are referred (i.e.

reference surface

such as MSL)

DefinitionsA plane perpendicular

to the local direction of

gravity or local vertical

line (In plane surveying)

A line that follows the

local direction of

gravity as indicated by a

plumb line

Figure 4.1 Leveling terms., Textbook

Line perpendicular

to the vertical


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Definitions ….

Mean Sea Level (MSL):

Average elevation of the sea surface based on hourly tide gauge

measurements over a period of 19 years

Bench Mark (BM):

A permanent reference point with a known elevation (relative to

some datum, usually MSL)

Vertical Control:

A series of bench marks or other points of known elevationestablished throughout an area.


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LEVELING METHODS

BS FS

Level set up half way between

BM and X - equal BS and FS

"hBMX = BS - FS = 8.42 - 1.20 = 7.22

hX = 820.00 + "hBMX

DIFFERENTIAL LEVELING

G r a d u a t e d

r o a d

G r a d u a t e d

r o a d


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CURVATURE AND REFRACTION

Light rays passing through the earth’s atmosphere are refracted towards the

earth’s surface - so reading is reduced (lowered) by RH

Effect of Curvature and Refraction = hf = 0.574 M2 = 0.0206 F2 in feet

OR hm = 0.0675 K 2 in meters

where hf is in feet, hm is in meters, and

M = distance in miles; F = distance in 1,000ft; K = distance in Kms

e.g. For distances of 300ft hf = 0.0019 Distances of 100m hm = 0.00067


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ELIMINATING EFFECTS OF CURVATURE AND REFRACTION

e1 and e

2 are the Curvature and Refraction effects

e1 = e2 ONLY IF D1 = D2

ALWAYS KEEP FORE SIGHTS AND BACK SIGHTS BALANCED!!!!!


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TRIGONOMETRIC LEVELING

ZCD = V = S sin = S cos z

= H cot z

OR V = H tan

ZAB = hi + V - r OR ZB = ZA + hi + S sin - r

= ZA

+ hi + H cot z - r

V e r t i c a

l a n g l e

Z e n i t h

a n g l e


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EQUIPMENT FOR DIFFERENTIAL LEVILING


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SETTIN UP A LEVEL

• Start by placing the

tripod over the point

with the legs spread and

extended about halfway.

• You want to have the

plate as level as

possible.


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SETTIN UP A LEVEL

• Mount the instrument in the

center of the plate with the

shape of the instrument bottom

plate and the tripod plate shape

aligned

• Coarsely level the instrument by

adjusting the leg length of the

tripod. When looking at thelevel bubble, the bubble being

to that side indicates the high

side.


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SETTIN UP A LEVEL

• Adjust the instrument by

adjusting the leveling screws.

• The bubble is approximately

centered by using the thumb

and first finger of each hand to

simultaneously adjust the

opposite screws.

•Rotate the telescope by 90

0

andadjust the remaining leveling

screw until it is precisely

centered .A bubble follows the left thumb

when turning the screws

bubble


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Compensating Prism in Automatic Level

After level is roughly leveled using bulls-eye bubble, automatic compensator

orients line of sight in a horizontal plane


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LEVELING FIELD PROCEDURE

After leveling the instrument:• balance BS and FS

• Make sure rod will be visiblewhen instrument leveled at new position

Rod Person:• hold rod vertical

(plumb)

• move rod back and forth

(minimumreading noted)

• select TP’s thatare stable

Rod level


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LEVELING FIELD PROCEDURE

Differential Leveling Procedure:

• start with BS on starting BM

• take FS and BS on all intermediate points (TP’s)

• close with FS on ending BM


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FIELD OBSERVATIONS - LEVELING

Only center crosshair reading recorded


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PRECISION

FGCC Accuracy Standard…………………...….. C = m$

(K)

FGCC STANDARDS (Federal Geodetic Control Committee)

1st Order: m = 4 2nd Order, Class II: m = 8

1st Order, Class II: m = 5 3rd Order: m = 12

2nd Order, Class I: m = 6

where: m = constant ; K = total length of line in Kms; C = allowable error in mm

Other Standards ……… C = 0.02 $ n

where C = allowable error and n = number of setups

In example C = 0.02$

7 = 0.05 => meets the standard

These standards are used for expressing the QUALITY of the

measurements


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Lab: Location

Elv = 59.854 m


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Note:

• One set of measured data to be recorded for each

group in one of the field books during the leveling

procedure .

• Each person in the group must make a sketch in

his/her field book during the leveling procedure (thiswill be checked by the TA) and copy the measured

data at the end of the lab.

• Perform a closure analysis on your loop prior to

ending the lab. Share the result with the TA.

Documents

Lab2 Lecture2 Leveling