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