Horizontal Measurements

1
Horizontal Measurements

• ERE 371 Surveying for Engineers

2
Introduction

• Surveying based on measuring two quantities
• Measurement of linear distances

3
Horizontal Distance
A
B
4
Introduction

• Surveying based on measurement of two quantities
• Linear distance (lengths)
• Angular distance (angles)
• Measurement of linear distances
• Three ways to express distance between 2 points
• Most interested in H and V

• Often measure slope reduce to horizontal and
  vertical
• This section deals with horizontal measurements

5
Accuracy Issues

• Absolute accuracy
• Relative accuracy
• Field estimates

6
Methods

• Approaches
• Pacing
• Optical rangefinders
• Odometers
• Tacheometry (stadia or subtense)
• Taping
• Electronic Distance Measurement (EDM)
• Global Positioning System (GPS)
• Issues

7
Taping

• Issues
• Types of tapes
• Lengths

• Material types

8
Sources of Error in Taping

• Instrumental errors
• Natural errors
• Personal errors

9
Taping Corrections

• Issue
• Correctable situations

10
Electronic Distance Measurement

• Major advance in surveying
• Advantages of EDM
• Process

11
Electronic Distance Measurement
Transmitted Energy
Returned Energy
12
General Principle of EDM

• Electromagnetic energy
• Travels based on following relation

• Intensity modulate EM energy to specific
  frequency

13
General Operation of EDM

• Setting up
• EDM measures direct (slope) distance
• Must reduce to horizontal
• Use vertical or zenith angles

• Use change in elevation

14
Making the Measurement

• Energy modulated ? split into internal/external
  beams
• Repeat measurement
• Different modulations ? generate multiple
  frequencies
• Automatic in modern EDM instruments

15
Errors in EDM

• EDM errors expressed in two parts
• Constant error
• Proportional error
• Common range in accuracy
• ?(1 mm ? 1 ppm)
• ?(10 mm ? 5 ppm)

16
Sources of Errors in EDM

• Natural
• Instrumental
• Personal

17
Combining Errors in EDM

• Major error components
• Combined error estimate

18
The Future of EDM

• New ideas
• Advantages

19
GPS
20
Readings

• Chapter 6 sections 6.1 6.13, 6.17 6.24