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Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
TOPOGRAPHIC SURVEY - LEVELINGJean – Pierre BRICQUET (IRD - US OBHI)
WMO / OMM
Volta-HYCOS Project
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Presentation plan
Introduction
Leveling
Leveling techniques
Closing
Topographic profiles
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Objectives of topographic survey
The main objectives of topographic survey are to allow for the establishment of maps and graphic plans on which all information in connection with land topography and its natural and artificial details are represented under symbolic form.
The cartographic data will for instance guide one in the field or allow to study a building project.
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Cartography : it is the whole set of scientific, artistic and technical operations based on direct observations or on the use of a document in order to draw maps, plans and other means of expression.
Planimetry aims at representing horizontally the projection of all the points situated in the field. To that effect, distances between various points as well as the angles linking them should be measured.
Leveling or altimetry is the set of topographic operations allowing for the determination of the altitude of a reference point from a known altitude, after calculating the height between these two points.
Some definitions
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The reference networks
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The reference networks
• NGF, General levelling of France• IGN 69 (French National Geographic Institute)• Normal Null
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The information sources
The best source at national level is the National Geographic Institute :
• Coordinates• Projection parameters• Map reference Numbers• Description of points…
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The level
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The parts of the level
1 fixing screw 2 spring plate 3 focussing knob 4 fixing plate 5 eyepiece of the telescope6 sighting tube 7 micrometer knob
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Types of levels
The simple level
The automatic level
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The digital level
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The setting up
Screw
BubbleSpirit level
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The setting up
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The leveler
Spirit level on an ‘N2 WILD’ level
Direction of rotation of the screws
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Reticles
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Reading of the staffThe reticle of a level is generally made up of four threads:- The upper thread (s´), which gives the upper reading m1 on the staff; - the lower thread, which gives the reading lower m2 on the staff;- The leveler thread (n), which gives the middle reading m on the staff; - the vertical thread (v) allows for pointing to the staff.The reading on every thread is visually estimated to the nearest millimetre. The threads allow for obtaining an approximate value of the horizontal distance. For every reading, it is advisable to read the three horizontal threads so as to avoid reading mistakes: a checking is indeed carried out in the field that : m =( m1 +m2 )/2
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Positioning of the staffThe staff is a linear rule that should be held vertically (it is fitted with a spherical bubble) and placed on the point whose elevation is to be measured. The precision of its graduation and the manner the staff is held in position strongly impacts on the accuracy of the measured height. The classical staff is generally graduated in centimeters. Numbering is often in decimeters.
YES
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Reading of the angles
In degrees In radians
In degrees In radians
In degrees
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Checking of the level
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Moving
The staff and the level should NEVER be moved simultaneously
YES
YES
NO
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
NO !
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The leveling principle
Spirit level
Horizontal line
Staff
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Leveling technique
StaffHorizontal axisAltitude of Horizontal axis
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Calculation of differences in level
∑ −+= )(21 AVARZZ RR
thobs HHf Δ−Δ=
Staff
Staff
Optical level
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Calculation of differences in level
Climbing
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Calculation of differences in level
Descending
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Calculation of differences in level
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Altitudes
• Extension leveling• Plane leveling• Section leveling• Surface leveling
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Extension levelling
Reference point
Level
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Extension levelling
Staff
Level
Chain
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Plane levelling
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Plane levelling
Staff
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Leveling pegs
Pegs
Axis of staff
Altitude
Pegs
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Surface levelling
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Measurement of the distance
• Historically, by the base amplification method defined by a two-meter invar staff
• Presently, by electronic telemetry or tachometry• Also with a level using stadimetric threads.
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The scope is the distance from the level to the staff:
It varies following the equipment and the level of precision needed, and should be 60 m maximum in ordinary levelling and 35 m in precision levelling. To the extent possible, the operator should position the level at equal distance from A and B, so as to achieve the equality of the scopes.
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Measuring of distance
Yes
No
Wrong
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Measuring uncertainties
All measurements are always affected by some error. These are:
• Systematic errors• Accidental errors• Mistakes
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Error in the calibration of the staff;
Failure in the verticality of the staff: faulty bubble;
Tilting mistake of the optical axis: optical axis not at right angle with the main axis;
Defect in the operation of the compensator.
Measuring uncertaintiesSystematic errors
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
The parallax error which is a wrong focussing of the telescope;
a wrong fixing of the bubble;
reading mistake on the staff due to the estimation of the millimetre;
a wrong selection of intermediary point: unstable point;
the blazing of air: sighting below the staff nearer to the ground when the weather is hot should be avoided
Measuring uncertaintiesAccidental errors
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Measuring uncertainties
The following mistakes are noted:
fixing: forgetting to fix the bubble, jammed compensator;
reading: confusing of leveller line with stadimetricline; confusing of graduation or of units;
transcription on the notebook: wrong transcription of the value read.
Mistakes
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Leveling and closing
Staff
Clo
sing
Starting point
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Plane closing
∑=
−−=n
iiA Agonnf
1200).2(Angular closing :
cfX XXf −=Planimetric closing (as X) :
222ZYXL ffff ++=Linear closing :
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Weighted compensation
∑=
−= n
i
ji
jj
p
pfc
1
Compensation by the least squares
qn
vpmq
n
iii
−±=∑=1
2
0
).(VPVA t ..=
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Longitudinal section
NoWrong
Axis of a longitudinal profile
Or follow flood marks line
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Cross section
Real altitude
Benchmark
Altitude of flood (20.11.1927 : 144.06 m)
Left Bank Right Bank
Scales :
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Cross section
Wrong drawing
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Actual altitudeMain benchmark (from National Geographic Institute)
Secondary benchmark
Secondary benchmark
Projet Niger - HYCOS – Formation en hydrométrie
Eléments de Topographie – Nivellement , Niamey, Mai 2006
Imaginary Altitude
Secondary benchmarkSecondary benchmark
Main benchmark