An Intro to FGDC Geospatial Positioning Accuracy

Standards

ODOT Survey Leadership TeamJune 15, 2006

Salem, OR

Ken Bays, Geodesist Control SpecialistODOT Geometronics

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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.

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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).

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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.

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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.”

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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.

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FGDC Organization Chart

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FGDC Subcommittees

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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

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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.

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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.

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Expression of Precision (CEP= 50%)

CEP = 5 meters

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Expression of Precision (s = 68.3%)

s = 7.4 meters

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Expression of Precision (E90 = 90.0%)

E90 = 12.2 meters

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Expression of Precision (2s = 95.5%)

2s = 14.8 meters

NSSDA requires reporting accuracy at the 95% accuracy level.

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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

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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

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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

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Part 2, Geodetic Networks,FGDC Geospatial Positioning Accuracy Standards

• Table 2.1 -- Accuracy Standards• Horizontal, Ellipsoid Height, and Orthometric Height• ---------------------------------------------• Accuracy 95-Percent• Classification Confidence• ---------------------------------------------• Less Than or• Equal to:• 1-Millimeter 0.001 meters• 2-Millimeter 0.002 "• 5-Millimeter 0.005 "• 1-Centimeter 0.010 "• 2-Centimeter 0.020 "• 5-Centimeter 0.050 "• 1-Decimeter 0.100 "• 2-Decimeter 0.200 "• 5-Decimeter 0.500 "• 1-Meter 1.000 "• 2-Meter 2.000 "• 5-Meter 5.000 "• 10-Meter 10.000 "

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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.

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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

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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-007.3-1998, (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”: http://www.fgdc.gov/standards/projects/FGDC-standards-projects/accuracy/part3/progpas3 )

– NSSDA written by the FGDC Subcommittee for Base Cartographic Data

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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.

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National Standard for Spatial Data Accuracy

NSSDA Statistics

• 95% confidence level required

• Horizontal circular error

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NSSDA NMAS

Agencies set thresholds ortolerances for their productspecifications

Defined thresholds

95% confidence 90% confidence

Horizontal Accuracy1.7308 * RMSEr

Horizontal Accuracy1.5175 * RMSEr

Vertical Accuracy1.9600 * RMSEz

Vertical Accuracy1.645 * RMSEz

National Standard for Spatial Data Accuracy

Comparison of NSSDA with NMAS

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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.

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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.

Grazing Allotment Spatial Data Standard

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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.

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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. 4 - Not accurate within 1000 feet of the actual location.

Fire Water Source Data Standard

No confidence level stated.

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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.

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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.

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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.

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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.

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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.

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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.

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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

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2. Reporting “Expected Accuracy” Based on Published Tests in the Standard

This Table will be updated frequently with new test results.

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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

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Why test GPS accuracy?Manufacturers specifications are for open sites and long data setsOpen Sites:What the GPS salesman said.

Forested Sites: What can really happen in forested sites with short data sets.

13 meters

1 meter

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Forest Service GPS Test Networks(Appendix 4)

www.fs.fed.us/database/gps/

• 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

Networks of stations with known locations in various canopy types.

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Clackamas Test Network

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Clackamas Test NetworkPro XR Occupation Time

(Point Feature)

Accuracy Relative to Time

0

2

4

6

8

10

12

1 2 5 10 20 50 100 200 500 1000

Time in Seconds

Met

ers

2dR

MS

Forest - None Forest - RT Forest - RT & Post Forest - Post

Open - None Open - RT Open - RT & Post Open - Post

Place - Corrections

Confidence level is stated.

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Clackamas NetworkGeoExplorer 3 Occupation Time

(Point Feature)

Accuracy Relative to Time

0

5

10

15

20

25

30

35

40

1 2 5 10 20 50 100 200 500 1000

Time in Seconds

Met

ers

2dR

MS

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

Place - Receiver - Corrections

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Clackamas NetworkGarmin GPS Receivers

Garmin GPS AccuracyClackamas and open sites

0102030405060

eTrex 1Pos.

GPSIII+1 Pos.

GPSIII+60 Pos.

Map76Int. Ant.1 Pos

Map76Ext. Ant.1 Pos

Map76Int. Ant.60 Pos

Map76Ext. Ant.60 Pos

Me

ters

(9

5%

)

Open

Forest

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Clackamas Network

Summary of Accuracy Performance*

0

5

10

15

20

25

30

35

ProXR GeoXT Geo3 Garmin

Open Sites

Forested Sites

* “Your mileage may vary.”

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Test Results Published in the “Table of Expected Accuracies” in the Standard.

This Table will be updated frequently with new test results.

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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.

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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

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Citations and References

• FGDC Standards, http://www.fgdc.gov/standards

•http://www.blm.gov/nhp/efoia/wo/fy01/im2001-186attach1.pdf

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What do we do now?