Theodolite
Dr Ahmed Ragheb SCM 221 – Planimetric Surveying 1 Lecture 5
Faculty of Engineering and Technology
Structural Department - Year 1
Dr Ahmed Ragheb
(Planimetric Surveying 1)
SCM 221
Theodolite
Dr Ahmed Ragheb SCM 221 – Planimetric Surveying 1 Lecture 5
Basic Definition
1
Theodolite
Dr Ahmed Ragheb SCM 221 – Planimetric Surveying 1 Lecture 5
According to reading method
Vernier Optical Digital
Very old and
obsolete
Hz are VL circles
are made from
glass and the
reading are taken
by circle reading
eyepiece
Angular readings
are displayed
digitally on screen
Types of Theodolite
2
Theodolite
Dr Ahmed Ragheb SCM 221 – Planimetric Surveying 1 Lecture 5
Theodolite Components
3
ALIDADE
Theodolite
Dr Ahmed Ragheb SCM 221 – Planimetric Surveying 1 Lecture 5
Theodolite Components
4
Telescope
Reticule
Theodolite
Dr Ahmed Ragheb SCM 221 – Planimetric Surveying 1 Lecture 5
0
<ABC
A
C
B
Horizontal angle <ABC = θ = HCRC – HCR
A
Concept of measuring Horizontal Angle
HCR
A
HCRC
Spatial Directions are projected on the horizontal circle of
the theodolite, and so Horizontal Circle Readings (HCR) are obtained
Horizontal Circle
5
Hz angle: It is the angle between the projection of two lines on the
horizontal plane passing by the theodolite clockwise direction
If θ –ve, then add 360
θ
What is important is the difference between readings not the reading itself
Hz circle fixed and pointer
moves with alidade o
Theodolite
Dr Ahmed Ragheb SCM 221 – Planimetric Surveying 1 Lecture 5
h
VL
Vertical angle (V)
Concept of measuring Vertical Angle
+ve Elevation Angle
-ve Depression Angle
Hz Plane
6
It is the angle measured in the vertical plane between the line joining the
theodolite-target (line of sight) and the horizontal plane passing by the theodolite
V = 90 – Z
Face Left (FL): VL circle left of observer
Face Right (FR): VL circle right of observer
hi
Theodolite
Dr Ahmed Ragheb SCM 221 – Planimetric Surveying 1 Lecture 5
Concept of measuring Vertical Angle
90
180
270
0
A
FL
VCRL
90
0
270
180
A
VCRR
VL = 90 – VCR
L
V
V V
VR = VCR
R – 270
Pointer or
index fixed
and VL circle
moves with
telescope
7
Turn alidade 180 and telescope 180
o o
FR
Index
Theodolite
Dr Ahmed Ragheb SCM 221 – Planimetric Surveying 1 Lecture 5
Index Error
90
180
270
0
A
VCRL
90
0
270
180
A
VCRR
VL = 90 – VCR
L – δ V
R = VCR
R – 270 + δ
δ δ
δ δ
V V
8
FL FR
Theodolite
Dr Ahmed Ragheb SCM 221 – Planimetric Surveying 1 Lecture 5
Since VL = V
R (for the same point)
How to determine Index Error?
Index error (δ)= (360 – [VCRL+VCR
R])
2
90 – VCRL – δ = VCR
R – 270 + δ
2δ = 270 + 90 – VCRL – VCR
R
If δ = –ve, then index inclined in opposite
direction, substitute normally with –δ
9
If (VCRL+VCR
R)≠360, then index error exists