1. An Intro to FGDC Geospatial Positioning Accuracy Standards
ODOT Survey Leadership Team
June 15, 2006
Salem, OR
Ken Bays, Geodesist Control Specialist
ODOT Geometronics

2. Why Adopt an Accuracy Standard?
Provide direction for testing and reporting accuracy of geospatial data.
Provide direction on matching equipment and field procedures to various geospatial data accuracy requirements.
Match the accuracy requirement to the job need, and not allow technology to dictate the accuracy.

3. What is the FGDC?
The Federal Geographic Data Committee (FGDC) is an interagency committee that promotes the coordinated development, use, sharing, and dissemination of geospatial data on a national basis. This nationwide data publishing effort is known as the National Spatial Data Infrastructure (NSDI).

4. What is the NSDI?
The NSDI is a physical, organizational, and virtual network designed to enable the development and sharing of this nation's digital geographic information resources.
NSDI includes the National Spatial Reference System (NSRS), a data base of geodetic control maintained by the National Geodetic Survey.

5. Why Model Standards to Comply with FGDC Standards?
Executive Order 12906, Coordinating Geographic Data Acquisition and Access: the National Spatial Data Infrastructure: “Federal agencies collecting or producing geospatial data, …. shall ensure, …., that data will be collected in a manner that meets all relevant standards adopted through the FGDC process.”

6. Why Model State Standards to be FGDC Compatible?
Building an effective NSDI requires a well-coordinated effort among Federal, tribal, State, local government, and academic institutions, as well as a broad array of private sector geographic, statistical, demographic, and other business information providers and users.
Involving these stakeholders in the development of the NSDI addresses nationwide data needs of end-users.
FGDC standards have been accepted by many state and local agencies and private firms.
Provides more efficiency and confidence when exchanging geospatial data.

7. FGDC Organization Chart

8. FGDC Subcommittees

9. Overview of FGDC Geospatial Positioning Accuracy Standards
Part 1: Reporting Methodology: common accuracy reporting for all geodata types.
Part 2: Geodetic Networks
Part 3: National Standard Spatial Data Accuracy: for digital geospatial data that is not constrained by scale.
Part 4: Architecture, Engineering, Construction, and Facilities Management
Part 5: Navigation Charts and Hydrographic Surveys

10. Part 1:Reporting Methodology, FGDC Geospatial Positioning Accuracy Standards
OBJECTIVE: To provide consistency in reporting the accuracy of point geospatial data collected by different activities (e.g., geodetic surveying, topographic mapping, bathymetric mapping, facilities management, mapping, cadastral surveying, etc.)
OBJECTIVE: Develop a FGDC document with a single methodology that defines how to report the positional accuracy for all point geospatial data collected, produced, or disseminated by the Federal government and the Nation.
Accuracy reporting for all geospatial data is required to be reported at the 95% confidence level.

11. Part 1: Accuracy Standard
Horizontal: radius of a circle of uncertainty, such that the true or theoretical location of the point falls within that circle 95-percent of the time.
Vertical: linear uncertainty value, such that the true or theoretical location of the point falls within +/- of that linear uncertainty value 95-percent of the time.

12. Expression of Precision (CEP= 50%)
CEP = 5 meters

13. Expression of Precision (ss = 68.3%)
ss = 7.4 meters

14. Expression of Precision (E90 = 90.0%)
E90 = 12.2 meters

15. Expression of Precision (2ss = 95.5%)
NSSDA requires reporting accuracy at the 95% accuracy level.
2ss = 14.8 meters

16. Part 2, Geodetic Networks, FGDC Geospatial Positioning Accuracy Standards
Developed by the FGDC Federal Geodetic Control Subcommittee (FGCS).
Objective: provides a common methodology for determining and reporting the accuracy of horizontal coordinate values and vertical coordinate values for geodetic control points

17. FGDC Federal Geodetic Control Subcommittee (FGCS)
Provide Leadership in:
leadership in coordinating the planning and execution of geodetic surveys
developing standards and specifications for these surveys
exchange of geodetic survey data and technical information

18. FGCS Work Groups Fixed Reference Stations Work Group
Instruments Work Group
Methodology Work Group
Wrote Part 2, FGDC Geospatial Positioning Accuracy Standards
Spectrum Issues Work Group
Vertical Reference Systems Work Group

19. Part 2, Geodetic Networks, FGDC Geospatial Positioning Accuracy Standards
Table Accuracy Standards
Horizontal, Ellipsoid Height, and Orthometric Height
Accuracy 95-Percent
Classification Confidence
Less Than or
Equal to:
1-Millimeter meters
2-Millimeter "
5-Millimeter "
1-Centimeter "
2-Centimeter "
5-Centimeter "
1-Decimeter "
2-Decimeter "
5-Decimeter "
1-Meter "
2-Meter "
5-Meter "
10-Meter "

20. Many sources were consulted during the preparation of this document.
BLM/ Forest Service “Standards and Guidelines for Cadastral Surveys using Global Positioning System Methods”.
Compliant with FGDC Geospatial Positioning Accuracy Standards Parts 1 and 2.
Many sources were consulted during the preparation of this document.
These sources included other GPS survey standards and guidelines, technical reports and manuals.
These standards and guidelines do not require that cadastral surveys be performed to the higher accuracy and methodology requirements of geodetic control surveys.
They are intended to provide sufficient observational and occupational redundancy to detect blunders and quantitatively demonstrate the stated accuracy of a survey has been achieved.

21. Part 2, Geodetic Networks, FGDC Geospatial Positioning Accuracy Standards
Old vs new
Proportional 1:100,000
1st order
New :positioanl toleraance
95 % confidence accuracy bands
Network vs local error

22. Part 3: FGDC Geospatial Positioning Accuracy Standards: The National Standard for Spatial Data Accuracy (NSSDA)
FGDC Geospatial Positioning Accuracy Standards Part 3, NATIONAL STANDARD FOR SPATIAL DATA ACCURACY, FGDC-STD , (NSSDA) implements a testing and statistical methodology for positional accuracy of fully georeferenced maps and digital geospatial data, in either raster, point, or vector format, derived from sources such as aerial photographs, satellite imagery, and ground surveys.
“The NSSDA is intended to replace the 1947 National Map Accuracy Standard.” (source: “A proposal for a National Spatial Data Infrastructure Standards Project”: )
NSSDA written by the FGDC Subcommittee for Base Cartographic Data

23. Why a GIS accuracy standard should is based on the NSSDA
GIS data is fully georeferenced digital geospatial data, which is the type of data addressed by the NSSDA.
Many Federal agency legacy GIS themes are referenced to NMAS requirements, and NSSDA is intended to replace NMAS.

24. National Standard for Spatial Data Accuracy
NSSDA Statistics
95% confidence level required
Horizontal circular error

25. National Standard for Spatial Data Accuracy
Comparison of NSSDA with NMAS

26. Existing OR/WA BLM Accuracy Attributes
Some BLM GIS Data Standards refer to NMAS. The NMAS has a 90% confidence level specified, and this can easily be converted to the NSSDA 95% confidence level.
Other themes have accuracy reporting attributes, but do not require that a confidence level be stated about the accuracy.

27. Grazing Allotment Spatial Data Standard
GRAZING_ALLOTMENT_BOUNDARY_LINE_ACCURACY_CD (ACCURACY)
Description
[Required] Locational accuracy code which indicates how close to the true geographic location on the ground a GIS entity has been recorded. There are two aspects to accuracy: the tools used to get spatial entities into a GIS (turned into digital representations), and the actual accuracy - how far off (+ or - feet) is the digital product. Three types of tools are recognized: GPS (global positioning system), manuscripting onto a map or photo, and legal descriptions using Township, Range, and Section. FOIA Category = Public
Allowable Codes :
GPS GPS1 = within 3 feet.
GPS2 = within 30 feet.
GPS3 = within 300 feet
No confidence level stated.

28. Noxious Weeds Spatial Data Standard
LOCATIONS_ACCURACY_CODE (ACC)
Description
[Required]
Locational accuracy code which indicates how close to the true geographic location on the ground a GIS entity has been recorded. There are two aspects to accuracy: the tools used to get spatial entities into a GIS (turned into digital representations), and the actual accuracy -- how far off (+ or _ feet) is the digital product. Three types of tools are recognized: GPS (global positioning system), Manuscripting onto a map or photo, and legal descriptions using Township, Range, and Section.
Also note that ACC is NOT a source for polygon overlap. If there is a change in accuracy, the old region is replaced by the new. Only the most accurate regions are maintained on these coverages.
FOIA Category = Public
Annotation
Locational Accuracy Codes:
GPS
GPS1 = within 3 feet.
GPS2 = within 30 feet.
GPS3 = within 300 feet.
No confidence level stated.

29. Fire Water Source Data Standard
Codes
The purpose of noting spacial accuracy is to give the potential user an idea of the reliability of finding the water source in the location as depicted in the theme. The methods of capturing the information and placing the location on the theme will effect the accuracy of the point. The code values represented here are an attempt to express what is the reasonable expectation of finding the water source within the given parameters as coded.
One of the following codes must be used:
1 - Within 10 feet of the actual location.
2 - Within 100 feet of the actual location.
3 - Within 1000 feet of the actual location Not accurate within 1000 feet of the actual location.
No confidence level stated.

30. Wildlife Observation Sites Data Standard
Name: LOCATION_ACCURACY_CODE
Description
[Required]
Attachment 1-15
Locational accuracy code which indicates how close to the true geographic location on the ground a GIS entity has been recorded. There are two aspects to accuracy: the tools used to get spatial entities into a GIS (turned into digital representations), and the actual accuracy - how far off (+ or - feet) is the digital product. Three types of tools are recognized: GPS (global positioning system), Manuscripting onto a map or photo, and legal descriptions using Township, Range, and Section. Also note that ACC is NOT a source for polygon overlap. If there is a change in accuracy, the old region is replaced by the new. Only the most accurate regions are maintained on these coverages. FOIA Category = Public
Codes
Locational Accuracy Codes:
GPS GPS1 = within 3 feet.
GPS2 = within 30 feet.
GPS3 = within 300 feet.
No confidence level stated.

31. Interim Ground Transportation Data Standard
43, Spatial Data Source:
Resource Grade GPS 3-7 meters (differential correction)
Submeter Grade GPS (differential correction)
No confidence level stated.

32. Geographic Coordinates Data Standard (GCDB)
Point Reliablility Code attribute with a list of values allowable including the following:
0 = Default/unknown
1 = 1 foot or less
2 = 3 feet or less
3 = 10 feet or less
4 = 40 feet or less
5 = 100 feet or less
6 = 200 feet or less
No ____?______ __?__ stated.

33. Recommendation in the Draft BLM Standard
In order to be in compliance with FGDC Geospatial Positioning Accuracy Standards, it is recommended that the accuracy attribute fields of BLM GIS Data Standards be revised and updated to eliminate outdated GPS accuracy references and to require reporting of accuracy at the 95% confidence level.

34. The Standard Provides Two Ways to Document the Accuracy of GPS data:
1. Test your own data set per procedures outlined in the Standard, and then report the actual “tested accuracy”,
or,
2. Report the “expected accuracy” of your GPS based on test results published in the standard of the same equipment used under similar conditions.

35. 1. Testing Your Own Data
A detailed explanation of how to test and report the accuracy of your GPS data set is provided in the Standard.

36. Metadata when you test your data
Report accuracy at the 95% confidence level for data tested for horizontal accuracy as:
Tested ____ meters/feet accuracy (horizontal) at 95% confidence level

37. 2. Reporting “Expected Accuracy” Based on Published Tests in the Standard
This Table will be updated frequently with new test results.

38. Metadata when you use Table
Report accuracy at the 95% confidence level for data produced according to established procedures to comply with intended horizontal accuracy values as:
Compiled to meet ____ meters/feet accuracy (horizontal) at 95% confidence level

39. Why test GPS accuracy? Manufacturers specifications are for open sites and long data sets
What the GPS salesman said.
1 meter
Forested Sites:
What can really happen in forested sites with short data sets.
13 meters

40. Forest Service GPS Test Networks (Appendix 4) www. fs. fed
Forest Service GPS Test Networks (Appendix 4)
Networks of stations with known locations in various canopy types.
Powell, Idaho: old growth cedar and spruce trees
Lubrecht, Montana: mixed lodgepole and ponderosa pine
Clackamas, Oregon: heavy second growth Douglas-fir and western hemlock
Bedford, Indiana: dense canopy eastern hardwood
Newtown Square, PA: heavy deciduous canopy

41. Clackamas Test Network

42. Clackamas Test Network Pro XR Occupation Time (Point Feature)
Confidence level is stated.
Accuracy Relative to Time 12 10 8
Meters 2dRMS 6 4 2 1 2 5 10 20 50
100
200
500
1000
Time in Seconds
Place - Corrections
Forest - None
Forest - RT
Forest - RT & Post
Forest - Post
Open - None
Open - RT
Open - RT & Post
Open - Post

43. Clackamas Network GeoExplorer 3 Occupation Time (Point Feature)
Accuracy Relative to Time 40 35 30 25
Meters 2dRMS 20 15 10 5 1 2 5 10 20 50
100
200
500
1000
Time in Seconds
Place - Receiver - Corrections
Forest - Geo III - None
Forest - Geo III - Post
Forest - Geo III ext - None
Forest - Geo III ext - Post
Open - Geo III - None
Open - Geo III - Post
Open - Geo III ext - None
Open - Geo III ext - Post

44. Clackamas Network Garmin GPS Receivers

45. Clackamas Network Summary of Accuracy Performance*
* “Your mileage may vary.”

46. Test Results Published in the “Table of Expected Accuracies” in the Standard.
This Table will be updated frequently with new test results.

47. What this Standard does NOT do
Does not define threshold accuracy values.
Does not dictate the minimum accuracy required for a given GIS theme.
The GIS specialist and data steward are responsible for deciding the accuracy values that are required on a theme-by-theme basis.

48. Recommendations
All Federal Accuracy Standards should be compliant with FGDC requirements.
The FGDC National Spatial Data Accuracy Standard it the FGDC Standard that is relevant to fully-georeferenced data.
The accuracy attributes of existing BLM GIS Data Standards should be updated to eliminate outdated GPS accuracy references and to require reporting of accuracy per NSSDA requirements at the 95% confidence level

49. Geospatial Positioning Accuracy Standards, Part 4: Architecture, Engineering, Construction, and Facilities Management
PART 4 provides accuracy standards for engineering drawings, maps, and surveys used to support planning, design, construction, operation, maintenance, and management of facilities, installations, structures, transportation systems, and related projects. 
It is intended to support geospatial mapping data used in various engineering documents, such as architectural, engineering, and construction (A/E/C) drawings, site plans, regional master planning maps, and related Geographical Information System (GIS), Computer-Aided Drafting and Design (CADD), and Automated Mapping/Facility Management (AM/FM) products. 
These products are typically created from terrestrial, satellite, acoustic, or aerial mapping techniques that output planimetric, topographic, hydrographic, or feature attribute data
Responsible FGDC Group: Facilities Work Group (Corp of Engineers)

50. Citations and References
FGDC Standards,

51. What do we do now?

52. Reporting: National Standard for Spatial Data Accuracy
Reporting accuracy of a dataset with data of varying accuracies:
If data of varying accuracies can be identified separately in a dataset, compute and report separate accuracy values. (for example GPS data)
If data of varying accuracies are composited and cannot be separately identified AND the dataset is tested, report the accuracy value for the composite data.
If a composited dataset is not tested, report the accuracy value for the least accurate dataset component.