1. Datums & Coordinate Systems
GPS for Ologists
Summer 2005
Revenge of the Shift
Joel.
After Post Field 1 Export.
This provides overview of Datums and Coordinate Systems. Setting the Stage
NAD27 Datum
National Park Service - Pacific Islands GIS Field Technical Support Center

2. Objective Identify different datums
GPS for Ologists
Summer 2005
Objective
Identify different datums
Identify different coordinate systems
A quick overview of coordinate systems, datums and their relationship with the way you collect data using space-based technologies and align those data with other data in a GIS.
Once we have learned there are differences it will be important in the following days to learn how to Identify what you got and Make it Match
National Park Service - Pacific Islands GIS Field Technical Support Center

3. Setting The Stage GPS is rigid – collects one way
GPS for Ologists
Summer 2005
Setting The Stage
GPS is rigid – collects one way
GIS is flexible – designed to share
#1 reason GPS data doesn’t line up in GIS - coordinate system/datum mismatch
How do we fix it? – Educate
Think about it. GPS really is amazing. You can spend less than a $100 and take one of these gizmos outside and within moments get coordinates of astounding accuracy (you can also spend $25,000 and get coordinates that are no better, at least for a stand-alone unit). But realize there is a LOT going on in the background in order to get those final coordinates.
GPS is high tech. And high tech is complicated. That’s the way it is. And that’s really what this presentation is all about. GPS for consumer use is one thing. But GPS used to provide professional services is entirely something else. It is the responsibility of the professional to understand the technology he or she is using to provide professional services.
GIS is all about sharing information ideally across the continent. Its an ideal digital melting pot and doesn’t care about what you use.
You should care though when you are using submeter GPS. This equipment found in this class is not recreational in nature, but designed to submit data of high quality into a GIS for archiving. Handling data in the submeter range takes good solid techniques.
This is a difficult topic and often the number one reason why maps don’t line up. There’s no pill you can take to learn this stuff, you just have to slog your way through it.
National Park Service - Pacific Islands GIS Field Technical Support Center

4. Coordinate Systems Latitude and Longitude
GPS for Ologists
Summer 2005
Coordinate Systems
Latitude and Longitude
Universal Transverse Mercator (UTM)
The two prominent location referencing systems used to make maps. These are latitude/longitude (Lat/long) and Universal Transverse Mercator (UTM).
National Park Service - Pacific Islands GIS Field Technical Support Center

5. Lat / Long Coordinate System Latitude
Parallels of latitude
0° latitude
north
latitude
south
90°N
equator

6. Lat / Long Coordinate System Longitude
Grenwich, England
West
Longitude
Meridians of longitude
0° longitude
Prime Meridian
East
longitude

7. UTM Coordinate Systems
GPS for Ologists
Summer 2005
UTM Coordinate Systems
A plane coordinate system to relate the coordinates of points on earth’s curved surface with the coordinates of the same points on a plane or flat surface
This slide needs work.
Allows projection of a spherical surface onto a flat surface
National Park Service - Pacific Islands GIS Field Technical Support Center

8. UTM Zones in North America
GPS for Ologists
Summer 2005
174
180
168
162
156
150
144
138
132
126
120
114
108
102 96 90 78 72 54 60 66 84 48
Seque,
Because both lat/long and UTM have their axis at an abstract location in space, both are relative to the shape of the Earth, which is represented in a datum. In mapping, datums represent the point or line of reference that is used as a starting location for measurement. As our understanding of the shape of the Earth has changed, the frame of reference (i.e. datum) for mapping has changed, and the “starting point” from which we measure has changed as well.
National Park Service - Pacific Islands GIS Field Technical Support Center

9. “Figure” of the Earth Best-fit ellipsoid (e.g., GRS-80, WGS-84)
GPS for Ologists
Summer 2005
“Figure” of the Earth
Best-fit ellipsoid
(e.g., GRS-80, WGS-84)
The Figure of the earth:
The globe is kinda squished, Its lumpy and irregular in shape but we have to assign something simple to define this squished shape. We call this an ellipsoid. Both LAT/Long and UTM are relative to the shape of the Earth, which is represented by a datum.
National Park Service - Pacific Islands GIS Field Technical Support Center

10. Datum and Ellipsoids Datum - represented by ellipsoid
Reference ellipsoid examples:
Clarke 1866
GRS 80
WGS 84

11. Common Geographic Datums
GPS for Ologists
Common Geographic Datums
Summer 2005
NAD27
NAD83
WGS84
ITRF00
In the US, GIS personnel are most likely to encounter three horizontal reference map Datums NAD27
NAD83
WGS84
ITRF00 – Global geodetic system used mainly in scientific studies.
National Park Service - Pacific Islands GIS Field Technical Support Center

12. NAD27: Clarke 1866 ellipsoid origin in Kansas
GPS for Ologists
NAD27: Clarke 1866 ellipsoid origin in Kansas
Summer 2005
Datum Origin on Surface of Earth
As I see it, NAD27’s biggest problem is that the datum origin is on the surface of the earth and it’s second biggest problem is that the Clark 1866 ellipsoid just doesn’t work as you leave the vicinity of Meades Ranch. Be careful, the diagram looks like you’re saying NAD27 is ECEF.
Ellipsoid Model based on less precise surveys
National Park Service - Pacific Islands GIS Field Technical Support Center

13. NAD27: Leaving Behind Invented Space Travel
GPS for Ologists
Summer 2005
NAD27: Leaving Behind
Invented Space Travel
Increasing accuracy of surveys
Shift from optical surveys to a mathematical model of the Earths shape
The result is a specific point on the landscape can take on multiple meanings
So over time, as we invented space travel, increased accuracy of surveying the science of mapping our earth shifted from optical surveys to a mathematical model of the Earths shape. The result is that any specific point on the earth can take on multiple meanings.
National Park Service - Pacific Islands GIS Field Technical Support Center

14. GPS Datum: WGS 84 Origin is at the Earth’s center of mass (geocentric)
GPS for Ologists
Summer 2005
GPS Datum: WGS 84
Origin is at the Earth’s center of mass (geocentric)
This is the datum used for the NAVSTAR GPS satellites
National Park Service - Pacific Islands GIS Field Technical Support Center

15. WGS84: WGS84 ellipsoid origin center of earth
GPS for Ologists
Summer 2005
WGS84: WGS84 ellipsoid origin center of earth
The origins of the WGS84 and NAD83 ellipsoids are at the center of the earth’s mass, which makes them ideal for a GPS datum
National Park Service - Pacific Islands GIS Field Technical Support Center

16. Datum Adjustments Known as Datum Adjustments or Epochs
GPS for Ologists
Summer 2005
Datum Adjustments
Known as Datum Adjustments or Epochs
WGS84 (G1150) – most current version
“Original” NAD83 = NAD83 (1986)
NAD83 (1992)
NAD83 (2002) ……
Most Current NAD83
NAD83 (CORS96) (Epoch )
Just when you thought all you had to learn was a Datum name like WGS84…
It’s a bit more complicated. As a datum is more precicesly defined or datums become adjusted over time as we learn more about the center of the earths mass. Satellite, gravity measurements all enhance the level of precision that we can measure things. Datums therefore are adjusted or realized using the term epochs. These datum reference frames are noted by a year (1986) or (1992).
Whats happened is that the most current realization of NAD83 and WGS84 differ by up to a meter. Errors can be introduced into a map by assuming these are the same
National Park Service - Pacific Islands GIS Field Technical Support Center

17. Over Time Datums Have Grown Apart
GPS for Ologists
Summer 2005
Over Time Datums Have Grown Apart
NAD83
NAD83 = WGS84
WGS84
~4+ feet
This slide works great. Shows the old and new (1986 what we knew then) and What we know now.
Do Note: at an even deeper level is that NAD83 has kept up with WGS84 as well. It’s just that this slide is a bit misleading, that there is not a NAD83 next to the modern WGS84. It is,,,, its called NAD83(CONUS) CORS96.
National Park Service - Pacific Islands GIS Field Technical Support Center

18. Differences between Datums
GPS for Ologists
Summer 2005
Differences between Datums
NAD27 ≠ NAD83 (1986)
33 to 700 feet
Many of you have seen these large differences between the older NAD27 and NAD83. Alaskan’s are often caught with seeing shifts exceed two football fields.
NAD27 Datum
National Park Service - Pacific Islands GIS Field Technical Support Center

19. Shift Happens - Redmond OR 2005 Example
GPS for Ologists
Shift Happens - Redmond OR 2005 Example
Summer 2005
710 Feet
Here is the shift in the GIS.
GIS baselayers are in NAD83. When a person transfers GPS data using PFO to GIS without switching to NAD83, then this Northern Displacement occurs – 710 Feet.
This causes confusion, delay and loss of confidence in Fire field and GIS staff.
National Park Service - Pacific Islands GIS Field Technical Support Center

20. Differences between Datums
GPS for Ologists
Summer 2005
Differences between Datums
WGS84 = ITRF00
about 2cm
NAD83 (CORS96) ≠ WGS84
about 4.3 feet
More subtle differences or error shifts can be seen here though when Errors can be introduced into a map by assuming these are the same
For Arcata
National Park Service - Pacific Islands GIS Field Technical Support Center

21. Reference Frames
Differentially corrected GPS data are always in terms of the corrections source’s reference frame.
In Arcata we are using CORS station data and therefore must apply the correct datum transform between the GPS data and your GIS

22. Mapping / Coordinate System
For Arcata BLM Office in Pathfinder Office
Coordinate System: UTM Zone 10N
Datum: NAD 83 (CONUS) CORS96
Accuracy Test on Friday

23. Reason Were Using NAD83 (CONUS) CORS96
GIS In NAD83
Using CORS96
CORS
ITRF00
~4+ feet

24. When Do Datums/Coordinate Systems Matter?
GPS for Ologists
Summer 2005
When Do Datums/Coordinate Systems Matter?
PFO Map View
Coordinate system
Terrasync
Coordinate System
Export Utility
Shape Export Coordinate System
ArcGIS Catalog
Define Projection
ArcGIS
Data Frame Properties – Coordinate System Tab
If we had to break the Datum shift issue into two areas where it matters most, its in the Field and in the GIS.
In the field when communicating between GPS users and when communicating or transferring data between GPS and paper maps. The classic example here is the dispatcher is in one datum and you, the user is in another datum.
In the GIS, after the data is stored and transferred into a Geographic Information system like arcView.
Projecting data on top of GIS data based in a different datum and/or coordinate system. The data is shifted relative to the base layers. This is a very common occurrence and can prove disastrous when the map is printed out the next day with the fire depicted on the wrong side of the road or the safety zone is in the wrong place. The GIST making the map never had the chance to visit the site, so confirmation of the data was impossible.
National Park Service - Pacific Islands GIS Field Technical Support Center

25. GPS Datum Tips Summary: Good handouts in <cd>/references
GPS for Ologists
Summer 2005
GPS Datum Tips
Summary:
Check, check, check
ASK your GIS Specialist
Good handouts in <cd>/references
National Park Service - Pacific Islands GIS Field Technical Support Center

26. GPS for Ologists
Summer 2005
Conclusion
Now that you’ve learned there are differences it will be important that you learn how to…
Make it Match
Pre-Field Day 2
Datum Transforms
Friday’s Test against Truth
The tools you are going to learn in these three days will give you the capability to set the appropriate export settings in PFO to match the coordinate system and datum of your GIS.
You Just learned there are differences.
You will be learning
How to Check (identify the coordinate/datum)
Make the Data Match
National Park Service - Pacific Islands GIS Field Technical Support Center

27. You are here GPS for Ologists Summer 2005
National Park Service - Pacific Islands GIS Field Technical Support Center

31. GPS for Ologists Revenge of the Shift
Matching Datums
GPS for Ologists
Summer 2005
I’m using WGS84
I use GPS for all my mapping. I’m using NAD83(1986)
Revenge of the Shift
Joels.
A short reiteration to always check. This is prior to transferring an image to the datalogger on Pre-Field 2. This was dropped in Arcata due to time constraints.
4.3 ft
National Park Service - Pacific Islands GIS Field Technical Support Center

32. GPS for Ologists
Summer 2005
Objective
Overview of Matching Datums and Coordinate Systems in Pathfinder Office and Data Transfer
National Park Service - Pacific Islands GIS Field Technical Support Center

33. Taking “GIS” out in the Field
Rasters
Vectors
All require a projection (coordinate system) defined ahead of time

34. Matching Data Steps Know what it is – Metadata helps
Tell Pathfinder Office the correct Datum and Coordinate System

35. When Do Datums/Coordinate Systems Matter?
GPS for Ologists
Summer 2005
When Do Datums/Coordinate Systems Matter?
PFO Map View
Coordinate system
Terrasync
Coordinate System
Export Utility
Shape Export Coordinate System
ArcGIS Catalog
Define Projection
ArcGIS
Data Frame Properties – Coordinate System Tab
If we had to break the Datum shift issue into two areas where it matters most, its in the Field and in the GIS.
In the field when communicating between GPS users and when communicating or transferring data between GPS and paper maps. The classic example here is the dispatcher is in one datum and you, the user is in another datum.
In the GIS, after the data is stored and transferred into a Geographic Information system like arcView.
Projecting data on top of GIS data based in a different datum and/or coordinate system. The data is shifted relative to the base layers. This is a very common occurrence and can prove disastrous when the map is printed out the next day with the fire depicted on the wrong side of the road or the safety zone is in the wrong place. The GIST making the map never had the chance to visit the site, so confirmation of the data was impossible.
National Park Service - Pacific Islands GIS Field Technical Support Center

36. Today’s Background Image
Humboldt Campus Map
PDF obtained from Website
Converted to TIFF
Co-registered 12 control points between Ortho
~ Depending on accuracy of Ortho, maybe +/- 20 meters in horizontal accuracy

37. Coordinate System and Datum
GPS for Ologists
Coordinate System and Datum
Summer 2005
At the time you obtain image file and world file, find out coordinate system and datum. If a projection file is available, then open file to find out information.
Coordinate System: UTM Zone 10N
Datum: NAD 83 (CONUS)
National Park Service - Pacific Islands GIS Field Technical Support Center

38. Next Step
Data Transfer background imagery to the GeoCE device

39. You are here GPS for Ologists Summer 2005
National Park Service - Pacific Islands GIS Field Technical Support Center

43. Getting it Right in Pathfinder Office
GPS for Ologists
Datum Transforms
Summer 2005
Getting it Right in Pathfinder Office
Joels Datum Part III.
Following Lauras Mapping Tools 3.
Some lecture on Accuracy, reiteration of differences in Datums. Introduce Reference Frames and walk the class thru a BAD and GOOD Export.
This requires folks to have collected a rover file with some point features on top of NAD83(CORS96) Truth. Export as BAD, then GOOD.
Pick up in Datum Transform 04B with the Steps in ArcGIS.
National Park Service - Pacific Islands GIS Field Technical Support Center

44. Objective
Identify the proper reference frame for different differential sources
Learn how to apply the correct datum transformation inside PFO

45. Prior to this Presentation
You occupied “Truth”
Collected at least one Point feature
Now we can compare!

46. Mapping Grade GPS Accuracy
Verification of accuracy is essential to gain confidence
We have to ensure we transform the data correctly to GIS

47. Accuracy Slides
Using Real Data.

48. Today is Your Chance to Test
First Some Background

49. NAD83 Developed Using WGS84
GPS for Ologists
Summer 2005
NAD83 Developed Using WGS84
Review
The origins of the WGS84 and NAD83 ellipsoids are at the center of the earth’s mass, which makes them ideal for a GPS datum
National Park Service - Pacific Islands GIS Field Technical Support Center

50. Over Time Datums Have Grown Apart
Review
NAD83
NAD83 = WGS84
WGS84
~4+ feet

51. Datum Adjustments Review Known as Datum Adjustments or Epochs
GPS for Ologists
Summer 2005
Datum Adjustments
Review
Known as Datum Adjustments or Epochs
WGS84 (G1150) – most current version
Most Current NAD83
NAD83 (CORS96) (Epoch )
Just when you thought all you had to learn was a Datum name like WGS84…
It’s a bit more complicated. As a datum is more precicesly defined or datums become adjusted over time as we learn more about the center of the earths mass. Satellite, gravity measurements all enhance the level of precision that we can measure things. Datums therefore are adjusted or realized using the term epochs. These datum reference frames are noted by a year (1986) or (1992).
Whats happened is that the most current realization of NAD83 and WGS84 differ by up to a meter. Errors can be introduced into a map by assuming these are the same
National Park Service - Pacific Islands GIS Field Technical Support Center

52. Differences between Datums
GPS for Ologists
Summer 2005
Differences between Datums
Review
WGS84 = ITRF00
about 2cm
NAD83 (CORS96) ≠ WGS84
about 4.3 feet
More subtle differences or error shifts can be seen here though when Errors can be introduced into a map by assuming these are the same
For Arcata
National Park Service - Pacific Islands GIS Field Technical Support Center

53. Reference Frames Review CORS Post Process = ITRF00
Autonomous GPS = WGS84 = ITRF00
WAAS = ITRF00
NDGPS (Radio DGPS) = NAD83 (CORS96)
OMNISTAR (Satellite DGPS) = NAD83 (CORS96)

54. “TRUTH” NAD 83 (2003.0) Anchorage
NAD 83 (CORS96) to WGS-84 (G1150)
This is essentially the CORS or WAAS Reference Frame
WGS-84 (G1150) = ITRF 00 (2001.0)
4.2 ft 
“TRUTH” NAD 83 (2003.0) Anchorage

55. Reference Locate this support doc and follow along
2nd to last reference in Notebook
SprtNote_PFO-GPSA_NAD83Datum.pdf

56. This Training Used Scenario 2

57. Since our Reference Frame is CORS
Our GPS data is corrected against a source that is in WGS84 or ITRF00
And our GIS is in NAD83
We therefore define an ITRF00 to NAD83 Transform

58. Export Out as NAD83 (CONUS) CORS96
The reason behind our class standard

59. To Keep Shifts at Bay
Verify reference frame of differential source

60. To Keep Shifts at Bay
Apply the correct datum transform before the Export depending on your GIS needs
Talk to your GIS Nerd

61. Summary
Identified the proper reference frame for different differential sources
Learned how to apply the correct datum transformation inside PFO
Keep Shifts at Bay by verifying and using the right transform

62. If You Use WAAS? Since WAAS is ITRF use NAD 1983 (Conus) CORS96
GPS for Ologists
Summer 2005
If You Use WAAS?
Since WAAS is ITRF use NAD 1983 (Conus) CORS96
Extra Slide
National Park Service - Pacific Islands GIS Field Technical Support Center

63. If You Use Coast Guard Beacon?
GPS for Ologists
Summer 2005
If You Use Coast Guard Beacon?
Since NDGPS is already in NAD83 (CORS96) use NAD 1983 (Conus)
No need to apply a transform.
Extra Slide
National Park Service - Pacific Islands GIS Field Technical Support Center

64. You are here GPS for Ologists Summer 2005
National Park Service - Pacific Islands GIS Field Technical Support Center