ORWEF Presentation March 2012 - Oregon Water Education Foundation GPS, GIS and stormwater mapping implementation

1. Susan K. Ottersen – GIS Specialist
Tim Kay – Collection Systems Tech
CLACKAMAS COUNTY – WATER ENIVRONMENT SERVICES

2. Outline of Presentation
 Section A: GPS
 Part 1: What is GPS?
 Part 2: Types of GPS units
 Part 3: GPS Errors
 Part 4: Collecting data
 Section B: GIS
 Part 1: What is GIS
 Part 3: Office Application
 Part 2: Why use GIS

3. Part 1: What is GPS?
 The Global Positioning System (GPS) is a satellite-
based navigation system made up of a network of 24
satellites placed into orbit by the U.S.
 The satellites circle the earth 2x a day in a very precise
orbit.
 Each satellite transmits a very low radio signal with its
location and unique identifier
 1 master Control station, 5 monitor stations, multiple
ground antennas

4. Part 1: What is GPS?
 Satellite Configuration

5. Part 1: What is GPS?
 Generating Location – MINIMUM OF 3 SATELLITES

6. Part 1: What is GPS
 WAAS - Wide Area Augmentation System
 2 satellites that hover in stationary positions over the
equator.
 Communication Satellite developed by the FAA to
augment GPS for air navigation
 Sits in the southern direction
 Real time measurements in the field to achieve better
than 1 metre accuracy

7. Part 1: What is GPS?
 Differential Corrections – removes atmospheric
interferences
 Either real time as with WAAS
 In the office with Post-Processing software

8. Part 2: Types of GPS

9. Part 2: Types of GPS
 Where To Start?
 Why GPS?
 Inventory, Analysis, Asset Management, Aging features,
 What will I be mapping?
 Point, line, or area features
 What are the accuracy needs
 Based on the size of the smallest feature, or smallest distance
between features.
 How will I store and use the data
 ESRI, MicroStation, Etak, Open Source programs

10. Part 2: Types of GPS
 Questions to ask?
 What resources are available
 User knowledge, designated employees
 Time frame
 How long do I have for the project
 Money
 Accuracy, cross uses, # of units, additional accessories, software

11. Part 2: Types of GPS Units
 Recreational ($100 - $1000)
 Garmin, Delorme, Magellan, Rand McNally, TomTom
 Scientific
 Trimble ProXT, SXBlue II, GISMapperTM 7, TomTom,
Magellan Professional MobileMapper
 Survey
 Leica, Nikon, Topcon ($2000 - $25k)

12. Part 2: Types of GPS Units
Recreational Professional
 Recreational receivers are
designed to acquire a location
fix quickly without the need for
pinpoint accuracy. Hikers,
bikers, hunters….. Outdoor
enthusiasts, this accuracy is
perfectly adequate, they can
generally find what they are
looking for once they get within
10 meters of it.
 Professional GIS users typically
require very accurate placement
of features, often within a meter
or better, so that data layers can
be overlaid and intricate spatial
relationships determined.

13. Part 2: Types of GPS Units
Recreational Professional
 Many are capable of real-time
differential correction, but DO
NOT have the ability to post
process.
 Even with the strongest, most
accurate differential correction
signal, recreational receivers are
simply not built to achieve
submeter accuracy
 Higher specifications on both
hardware and software in the
receiver.
 Ability for both real-time
differential correction, and post
processing

14. Part 2: Types of GPS Units
 With the increasing pressure to do more with less, the
lower price of a recreational receiver is significant,
however the inability for a ‘rec’ receiver to do the job,
outweighs the initial savings.
 Able to download data
 Programmable for your use

15. Part 2: Types of GPS Units
 To reliably achieve the submeter level of accuracy is
the professional GPS positioning is required.

16. Contributing factors
 GPS quality control
 Electromagnetic shielding
 Antenna technology
Part 3: GPS Errors

17. Part 3: GPS Errors
 Professional GPS units give users control over the
quality of the position points that are collected.
Through a simple interface, the user can establish
specific thresholds for acceptable data quality.
 These quality control settings essentially allow the user
to filter out any poor data that may degrade the overall
quality of the location coordinates, resulting in greater
accuracy in the final dataset.
GPS Control

18. Part 3: GPS Errors
 By their very nature, GPS signals are extremely weak
and are easily degraded by interference from nearby
electrical devices such as laptop computers. High end
GPS products are designed with advanced shielding
technology that MINIMIZES the affects of stray
electromagnetic signals from other equipment.
Electromagnetic Shielding

19. SIGNAL OBSTRUCTION
POWER LINES/TOWERS

20. Part 3: GPS Errors
 Acquisition of quality GPS signals requires a well-
tuned antenna. The antenna provided with
professional grade units are designed to allow poor
quality signals to be distinguished from high quality
signals.
 When receiving transmissions in built-up urban
environments and under tree canopy, there is
degradation of accuracy due to multipath signals.
Antenna Technology

21. SIGNAL OBSTRUCTION
TREE CANOPY

22. Part 3: GPS Errors
 GPS signals have been degraded by being reflected
from buildings and other overhead features on the way
to the receiver.
 While the antennas on professional receivers are
designed to recognize and filter out multipath signals,
many ‘rec’ receivers have no multipath mitigation at
all.
Antenna Technology, con’t

23. Part 3: GPS Errors
 This means that some ‘rec’ receivers appear to track
better than pro-grade receivers in difficult
environments, however, the positions derived from
these measurements may be so badly affected by the
multipath that relying on them is potentially worse
than having no position at all.
Antenna Technology, con’t

24. Part 3: GPS Errors
 Recreational units will typically collect all data, but
this ‘productivity’ can come at the expense of accuracy.
And data from a ‘rec’ unit contains insufficient
information to enable postprocessing.

25. SIGNAL OBSTRUCTION
WALLS AND BUILDINGS

26. Part 4: Field Observations Tim
 REMEMBER……WHEN GPS’ING TO THINK ABOUT THE
POTENTIAL OBSTRUCTIONS AROUND YOU 

27. Part 1: WHAT IS GIS?
 GIS = Geographical Information Systems
 Hardware, software and data for capturing, managing,
analyzing and displaying all forms of geographically
referenced information
whatisgis.wmv

28. Part 2: Office Application
Processing
 SSF > .Cor > .Shp > SDE
 Time consuming

29. Part 2: Office Application

30. Part 2: Office Application

31. Part 3: Why GIS & GPS

32. Part 3: Why GIS & GPS

33. Part 3: Why GIS & GPS
Next Phase – Asset Condition

34. Part 4: Fini
Questions?