Surveying Instruments

1
SurveyingInstruments

• Mechanical
• Tape
• Opto-Mechanical
• Level
• Transit/Theodolite
• Electronic
• Electronic Distance Measuring
• Total Station
• GPS Satellite Assisted Systems

2
Some Oldies
3
Some Oldies
4
Some Oldies
5
Some Oldies
6
Some Oldies
7
Some Oldies
8
Some Oldies
Wireless Communication Technology
9
Electronics Devices

• Electronic Distance Meter

10

• Total Station

11
GPS in Land Surveying
12
(No Transcript)
13
What is GPS?

• A system capable of providing position
• information anywhere on earth
• Global Positioning System
• Relies on using a constellation of orbiting
  satellites
• (various orbits around the earth)
• User receivers acquire signal and determines
  position

14
GPS

• Global Positioning System
• Developed by DOD
• Cost 10 billion
• Triangulation-based technology

15
Why use it?

• AAA (who can resist it!)
• All weather operation
• Always available (24/7 operation)
• Anywhere available
• Economical
• Increased Productivity
• Improved Customer service
• Accuracy (3-D data, Velocity and timing)

16
Who Uses it?

• Land, sea, and airborne navigation, surveying,
  geophysical exploration, mapping and geodesy,
  vehicle location systems, farming, transportation
  systems
• Telecommunication infrastructure applications
  include network timing and enhanced 911 for
  cellular users
• Global delivery of precise and common time to
  fixed and mobile users

17
Some Applications
18
Some Applications
19
Some Applications
20
Some Applications
21
Some Applications
22
Some Applications
23
Some Applications
Could be used to track mail if properly used!
24
Some Applications
25
Some Applications
26
Some Applications
Mapping
27
The GPS System ComponentsThe User Segment The
Control Segment The Space Segment
28
The Space Segment
29
The Space Segment

• Constellation of 24 satellites orbiting the earth
• Six orbital planes with four satellite per orbit
• Seven satellites are typically visible 10 degrees
  or more above the horizon
• Satellites orbit the earth about every 12 hours

30
Satellite Constellation
31
GPS Satellite
32
Basic Concept

• Satellites are reference points to locations on
  earth (their location are known)
• A location of a point on earth is identified by
  triangulation
• Signals from three satellites are used
• Travel time of each signal is determined
• Signals travel at Speed of light
• Distance Travel Time Speed of Light

33
Triangulation (2-D)
34
Triangulation (3-D)

• 3 satellites

35
The Triangulation Equation

• 3 variables
• Where, exactly, are the satellites
• How long it takes the radio signal to travel that
  distance
• How far is the point from the satellite

36
Where are the satellites?

• From orbital mechanics, the location of
  satellites are determined
• An almanac of orbital information for all
  satellites are stored in each satellite
• Ground control-stations continuously update
  location information of each satellite and
  transmit it to them (i.e. ephemeris)

37
GPS Codes Carriers
38
Pseudoranging
39
What is the Distance?

• Range (distance) Time Speed of Light
• Three satellites will provide
• Latitude
• Longitude
• Height
• Fourth satellite is needed to account for clock
  time difference solve for time

40
Pseudoranging to four Satellites
41
Accuracy of Pseudoranging

• P code 10 meters
• C/A code 20 to 30 meters
• With Selective Availability (SA) 100 meters
• SA was turned off since 2000
• Other techniques are needed to improve accuracy
• Carrier Phase measurement (Surveying)
• Differential GPS

42
Sources of Error

• Atmospheric scattering
• Clock errors
• Receiver errors
• Multi-Path Interference
• Ephemeris
• GDOP
• SA

43
Multi-path Error
44
GDOP(Geometric Dilution of Precision)
45
Differential GPS (DGPS)

• Two receivers used simultaneously
• One located at a control station (or a monument)
  where the coordinates are precisely known (base
  station)
• One is located at a survey point where
  coordinates are desired
• Both stations measure distance
• Base station calculates error and transmits it to
  the survey station

46
DGPS
47
Errors Compensated

• The adjustments made by DGPS technique represents
  a net sum of various errors present in the
  process.
• This correction doesnt address problems with the
  receiver clocks
• This correction may not be sufficient when the
  receiver and the base station are too far from
  each other

48
Grouping of Survey Points