Lab2 Lecture2 Leveling
Transcript of 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.