Lecture 1 -Leveling
In this lecture, we will provide a brief introduction to basic principles of
surveying and outline one of the most fundamental forms of surveying - leveling
Concepts Covered
1) Leveling
Definitions (benchmark, HI, backsight, foresight)
Basic theory of leveling
Leveling the instrument
Reading the survey rod
Booking your work
In-class survey
2) Discuss field assignment #1
3) Assign everyone into survey groups
4) Identify the location where we will all meet in the field
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Surveying – An Introduction
Definition:
The discipline encompassing all methods of gathering and processing
information about our physical earth and its environment.
Types of Surveys:
Cadastral Surveys (boundary surveying)
Hydrographic Surveys (involving water bodies)
Construction Surveys (engineering surveys)
Geodetic Surveying (locating points in space)
Topographic Surveys (ground-based mapping)
Photogrammetric Surveying (aerial methods)
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Field Work In This Course
Week 1 Leveling
Definition: The process of finding the elevation at a specified location
relative to another known elevation.
This week, each group will perform level surveying at a specified site on
the university campus.
We will break up into groups later in this lab.
Week 2 Taping
Week 3 Transit and Angles
Week 4 Field Survey for Course Project (Phase 1)
Week 5 Field Survey for Course Project (Phase 2)
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Leveling Equipment
Level
Levels are instruments used to establish a
horizontal line of sight.
Tripod
Leveling rod
Field Book, pencils, ruler or straight edge
Stakes, hammer, paint, ribbon
Hand level
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Definitions
Bench Mark (BM) A permanent object that has a known
elevation.
Temporary BenchMark (TBM) A moveable object that has a known
elevation.
Turning Point (TP) A fixed object used when determining
the elevation of other points.
Think of turning points as “stepping
stones” in your level survey.
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Height of Instrument (HI) The elevation of the line of sight established by
the instrument.
Backsight (BS) The reading on the rod when held on a known or
assumed elevation.
Backsights are used to establish the height of
instrument.
Foresight (FS) The reading on the rod when held at a location
where the elevation is to be determined.
Foresights are used to establish the elevation at
another location, often a turning point.
Intermediate Foresight (IFS) The reading on the rod when held at a location
where the elevation is to be determined but not
used as a turning point.
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Basic Theory
Leveling Rod
0.973 4.987
Backsight Foresight
Bench Mark Level and Tripod
Elevation 100.000
Computed Elevation = 95.986
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Calculations
For our leveling, we need to apply two very simple equations:
Height of Instrument = Known Elevation + Backsight
and
TP Elevation = Height of Instrument – Foresight
For the previous example:
Height of instrument = Known Elevation + Backsight
= 100.000 + 0.973
= 100.973
and
TP Elevation = Height of Instrument – Foresight
= 100.973 – 4.987
= 95.986
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Booking Your Work
Every surveyor in North America records his/her level surveys in the same
manner using the six columns displayed on the left-hand pages of your survey
field book. The columns are typically labeled as: station, backsight (BS), height
of instrument (HI), intermediate foresight (IFS), foresight (FS), and the last
column contains the elevation values.
We will use the column labeled IFS later. Here is how we would record our
values for the previous example.
Station BS HI IFS FS Elevation
(+) (-) (-)
BM 100.00
0.973 100.973
TP #1 4.987 95.986
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Arrangement of Cross Hairs
When you sight through the telescope, you will see a vertical and a horizontal
cross hair and two horizontal stadia hairs.
Stadia Hair
Cross Hairs
Stadia Hair
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Reading the Rod
Rod readings are taken using the centre cross hairs.
For now, ignore the presence of the stadia hairs.
Rod readings are taken to three decimal places (or the nearest millimetre).
Rod readings can be read to two decimal places with certainty.
Estimate the third decimal place
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The rod is delineated to the nearest hundredth of a metre (centimetre)
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3
5
3
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What is the reading for this rod sighting?
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2
3
2
Answer: 2.363
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What is the reading for this rod sighting?
3
1
Answer: 1.308
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Duties of the Rod Person
The rod must be plumb to give a correct reading.
No matter how much care is taken by the instrument person when reading
the rod, if the rod is not perfectly vertical when read, errors will result.
Waving
Waving is the procedure used to ensure that the rod is plumb when a
reading is taken.
The method consists of slowly rocking the top of the rod, back and
forth.
The instrument person continuously reads the rod and selects the lowest
value.
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Closure
For all differential leveling, it is good practice to close the leveling loop.
Closing the loop is accomplished by returning to the original starting point.
If we were to complete our level loop with complete accuracy, our computed final
elevation would be exactly the same as the benchmark elevation used to initiate
the survey.
This comparison of the starting elevation and the computed ending elevation is
termed closure.
The accuracy of the survey can be easily determined by comparing the sum of
the backsights with the sum of the foresights. They should be equal.
Depending on the precision required, permissible values for the closure of a level
loop can be specified.
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Setting Up the Level
1) The legs of the tripod must be tightened securely.
2) The legs of the tripod should be firmly pressed into the ground with the
tripod base plate roughly horizontal.
3) When leveling a four-screw level, the telescope is rotated until it is over
two opposite screws as shown below.
Leveling Screw
Telescope
Bubble
Left Thumb Right Thumb
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The telescope is leveled by using the thumb and first finger of both hands
to adjust the leveling screws until the bubble is approximately centred.
Rule #1
The leveling screws are ALWAYS turned in opposite directions by equal
amounts simultaneously. If one screw is rotated faster than the other,
the screws will either bind or the telescope will loosen.
Rule #2
The left thumb rule ….
The leveling bubble will always move in the
direction of your left thumb.
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4) Rotate the telescope 90 degrees until it is located over the other two
leveling screws as shown.
Right Thumb
Left Thumb
Again, level the telescope using the leveling screws.
5) When the scope is level, rotate the telescope another 90 degrees and make
any minor adjustments to level the instrument.
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6) Rotate the scope another 90 degrees and again, make any minor corrections
as required.
7) Continue rotating and leveling the scope until the instrument is fully level
along both axes.
8) As a final check, gently spin your telescope and allow it to come to rest, no
matter what direction it faces.
Examine your leveling bubble.
It should be exactly centred.
If it is not, repeat the entire leveling procedure.
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Differential Leveling
In the previous example, we established a new elevation relative to a nearby
benchmark. In actual practice, our site and the benchmark might be very far
apart. In order to transfer the benchmark elevation to our site, a process
called differential leveling is used.
With differential leveling, we make use of turning points (TP’s). Recall that
turning points are selected locations where we use a foresight to establish the
elevation.
We then move the instrument to a new location and take another backsight to
establish a new height of instrument.
We can then repeat the “foresight/move the instrument/backsight” sequence
until we establish the elevation at our desired location.
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Field Assignment #1
Instrument Tests.
Complete the following tests and document them fully in your field book.
1) Instrument Test #1 (level tube check)
2) Instrument Test #2 (cross hair check)
3) Instrument Test #3 (2 peg test)
Field Survey
Use standard differential leveling to establish the elevation at three
stations defining a closed traverse. Document your level survey in your field
book.
Your fieldwork must include at least four turning points (TP’s) and eight
separate instrument setups as shown on the following figure.
You must get your fieldbook signed by an instructor before you can leave.
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A2
A3
TP #3
A1
TP #4
TP #2
TP #1
BM
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Preparation for your first field survey
1) Carefully read pages 1-36 of your CIVE125/ENVE100 Measurement and
Surveying Notes.
Know how to care for your instrument.
Understand how to level your instrument.
Understand the three instrument tests.
Understand how to correct your closure error.
2) Check the weather forecast. (appropriate dress, sunscreen, etc.)
3) Meet at the equipment shed located beside Conrad Grebel College.
4) Be on Time !!
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Group Assignments
E1, E2, E3 Mike Muffels
E4, E5, E6 Jennifer Son
E7, E8, E9 Terry Ridgway
E10, E11, E12 Alison Sherk
E13, E14 Prof. Cascante
C1, C2, C3 Mike Muffels
C4, C5, C6, C7 Jennifer Son
C8, C9, C10, C11 Alison Sherk
C12, C13, C14, C15 Don Fraser
C16, C17, C18 Prof. Cascante
C19, C20, C21, C22 Terry Ridgway
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