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Proposal for a Forest Service GPS Data Accuracy Standard Forest Service 2003 Geospatial Conference Colorado Springs, Colorado Ken Chamberlain, BLM Oregon State Office About the Proposed GPS Data Accuracy Standard Background

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proposal for a forest service gps data accuracy standard

Proposal for a Forest Service GPS Data Accuracy Standard

Forest Service 2003 Geospatial Conference

Colorado Springs, Colorado

Ken Chamberlain, BLM Oregon State Office

background
Background
  • In April 2002 the FS GPS Steering Committee was directed by Chuck Dull, Assistant Director of Engineering, Geospatial Applications to develop a GPS Data Accuracy Standard.
  • The GPS accuracy standard is in response to requests from line and staff officers at the national, regional, and forest level.
  • The objective is to provide guidance on assessing the accuracy, quality, and suitability of GPS data used in GIS and Land Management
  • The DRAFT GPS Data Accuracy Standard document is available at:.
    • http://www.fs.fed.us/database/gps/gps_standards/GPS_Data_Standard.pdf
elements of gis data quality
Elements of GIS Data Quality
  • Lineage
  • Logical Consistency
  • Completeness
  • Attribute Accuracy
  • Positional Accuracy

The GPS Data

Accuracy Standard

covers these elements

  • Connectivity
  • Shape
  • Relative Position
  • Source Position
  • Horizontal Position
  • Vertical Position
  • “True” position
purpose of a gps data accuracy standard
Purpose of a GPS Data Accuracy Standard
  • Defines a method for testing and reporting GPS accuracy that is consistent with FGDC, National Standard for Spatial Data Accuracy (NSSDA).
  • Provides GPS Test data to aid matching GPS equipment and field procedures to GIS and mapping accuracy requirements.
  • Match any GPS accuracy to the project requirements and not allow technology to dictate the accuracy.
what the gps data standard does not do
What the GPS Data Standard does NOT do
  • Does not define threshold accuracy values.
  • Do not dictate the minimum accuracy required for a given GIS theme or Mapping application.
  • Does not specify receiver type and receiver configuration
  • Does not address Data lineage, logical consistency or completeness

Therefore:

  • The data steward or application manager are responsible for deciding the accuracy values that are acceptable on a theme-by-theme or application basis.
parts of gps data accuracy standard
Parts of GPS Data Accuracy Standard
  • Section 1: Introduction
  • Section 2: GPS Accuracy Testing Guidelines
  • Section 3: Table of Tested GPS Accuracy
  • Section 4: GPS Accuracy Reporting and Metadata
  • References
  • Appendices:
    • 1. Application of the GPS Data Accuracy Standard
    • 2. National Standard for Spatial Data Accuracy Spreadsheet
    • 3. Formulas: Horizontal Accuracy using NSSDA formulas
    • 4. USFS GPS Test Networks
    • 5. Existing Standards
development of the proposed gps data accuracy standard
Development of the proposed GPS Data Accuracy Standard
  • Based on a review of existing FS and Federal accuracy standards.
  • Designed to comply with the Federal Geographic Data Committee (FGDC), Geospatial Positioning Accuracy Standards Part 3, NATIONAL STANDARD FOR SPATIAL DATA ACCURACY, FGDC-STD-007.3-1998. (NSSDA).(Appendix 2)
  • Intended to define testing procedures that meet NSSDA and meet metadata report requirements by:
    • 1) using existing FS GPS test data
    • 2) Users testing their own data
why adopt fgdc requirements
Why adopt FGDC Requirements?
  • 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.”

1994

overview of fgdc geospatial positioning accuracy standards
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
part 1 reporting methodology fgdc geospatial positioning accuracy standards
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
  • 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.
part 3 national standard for spatial data accuracy nssda
Part 3: National Standard for Spatial Data Accuracy(NSSDA)
  • NATIONAL STANDARD FOR SPATIAL DATA ACCURACY, 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.” (“A proposal for a National Spatial Data Infrastructure Standards Project”, http://www.fgdc.gov/standards/documents/proposals/progpas3.html
  • NSSDA written by the FGDC Subcommittee for Base Cartographic Data
national standard for spatial data accuracy
National Standard for Spatial Data Accuracy
  • NSSDA Statistics
  • Compares data to higher order positions
  • Based on Root Mean Square Error (RMSE)
  • 95% confidence
  • Horizontal
    • circular error
    • If error is equal and normally distributed in both x and y, horizontal accuracy is 1.7308 * RMSEr
  • reports error in ground distance
fgdc geospatial positioning accuracy standards part3 national standard for spatial data accuracy
FGDC – Geospatial Positioning Accuracy Standards-Part3: National Standard for Spatial Data Accuracy
  • Compare Data with Independent Data Set of higher accuracy
  • N=20 minimum
  • RMSEr = sqrt[S((Xt-Xg)2+(Yt-Yg)2)/N]
  • Report Horizontal error at 95%= 1.73xRMSEr
  • Report accuracy as Tested or Compiled to meet
  • Report Accuracy in ground distance and units
publish test results in the table of tested gps accuracy as part of the standard
Publish Test Results in the “Table of Tested GPS Accuracy” as part of the Standard.

This Table is a “living document” will be updated with new test results.

reporting the standard provides two ways to document the accuracy of gps data
REPORTING: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 “intended accuracy” of your GPS based on test results published in the standard of the same equipment used under similar conditions.
1 testing your own data
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 and NSSDA.

metadata when testing your own data
Metadata when testing your own data
  • Report accuracy at the 95% confidence level for data testedfor horizontal accuracy as:
    • Tested ____ meters/feet accuracy (horizontal) at 95% confidence level
2 reporting accuracy based on published table of tested gps accuracy in the standard
2. Reporting Accuracy Based on Published “Table of Tested GPS Accuracy” in the Standard

This Table is a “living document” will be updated with new test results.

metadata when you use table
Metadata when you use Table
  • Report accuracy at the 95% confidence level for data produced according to established proceduresto comply with intended horizontal accuracy values as:
    • Compiled to meet ____ meters/feet accuracy (horizontal) at 95% confidence level
review four expressions of accuracy for the same 5 meter gps data set
REVIEW: Four Expressions of Accuracy for the same“5 Meter” GPS data set:

CEP = 5.0 meters

1ss = 6.0 meters

E90 = 9.1 meters

E95 = 10.4 meters

existing fs accuracy standards
Existing FS Accuracy Standards
  • Official FS GIS Data Dictionary (Peg Watry)
    • http://fsweb.wo.fs.fed.us/im/standards/gis/coredata/
  • Cartographic Specifications and Symbols, EM 7140-24, Part 7, Guidelines for Digital Map Updates. (GSTC)
    • http://fsweb.gsc.wo.fs.fed.us/standards/em714024.pdf
  • Specify National Map Accuracy Standard (NMAS). NMAS = 90% confidence level.
  • have reporting attributes for Data Source but do not state the required confidence level.
  • Many themes Contain Optimistic estimates of GPS accuracy
fs data dictionary layer cultural properties
FS Data Dictionary Layer: Cultural Properties

·  Heritage Resource Description

A Heritage Resource is a structure, building, etc…of historic or natural significance, cultural, educational or artistic importance, significant architectural characteristics or an entity being managed for indefinite preservation

Note: A polygon should be used if GPS or other data collection techniques can depict the resource with greater accuracy.

Horizontal Accuracy: Targeted to National Map Accuracy Standards (NMAS)

DATA SOURCE:

GPS - 2-5 Meter, 3-D survey 02

GPS - 2-5 Meter, 2-D survey 03

GPS - Survey Grade and Sub-meter 04

fs data dictionary layer roads and trails
FS Data Dictionary Layer: Roads and Trails

A coverage describing the spatial location of roads and trails within or in close proximity to an administrative unit.

Associated National Application: INFRA Travel Routes

Horizontal Accuracy: Targeted to National Map Accuracy Standards

(NMAS)

Note GPS antenna

DATA SOURCE:

GPS - 2-5 Meter, 3-D survey 02

GPS - 2-5 Meter, 2-D survey 03

GPS - Survey Grade and Sub-meter 04

No confidence level stated.

fs data dictionary layer fire history
FS Data Dictionary Layer: Fire History

Fire History polygons represent the final

mapped wildfire perimeter.

These data are maintained at the Forest / District level to track the area affected by fire. Spatial data is stored via a regions feature class due to overlapping fire perimeters.

Horizontal Accuracy: Targeted to National Map Accuracy Standards (NMAS)

SOURCE_CODE: the source of the geographic position of the arc

02 Global Positioning; 2 to 5 meter accuracy; 3D lock

03 Global Positioning; 2 to 5 meter accuracy; 2D lock

04 Global Positioning; <1 meter accuracy; survey grade

No confidence level stated.

recommendations for fs existing standards
Recommendations for FS existing standards
  • Accuracy attribute fields of FS GIS Data Dictionaries could be revised to require reporting of accuracy at the 95% confidence level per NSSDA.
  • Modify Source codes to remove outdated GPS references: GPS 2-5 meter (CEP), 2 D data, and software.
  • Develop specific accuracy requirements on theme or application basis.
why test gps accuracy manufacturers specifications are for open sites and long data sets
Why test GPS accuracy?Manufacturers specifications are for open sites and long data sets

Open Sites:

What the GPS salesman said.

1 meter

Forested Sites:

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

13 meters

forest service gps test networks
Forest Service GPS Test Networks

Networks of monumented points with known coordinates

established by higher order survey in various canopy types.

  • Powell, Idaho: old growth cedar and spruce trees
  • Lubrecht, Montana: mixed lodgepole and ponderosa pine
  • Clackamas, Oregon: heavy Douglas-fir and western hemlock
  • Bedford, Indiana: dense canopy eastern deciduous forest
  • Newtown Square, PA: heavy deciduous canopy

Testing coordinated by:

Missoula Technology Development Center

clackamas network pro xr point feature

Confidence level is stated.

Forest - None

Forest - RT

Forest - RT & Post

Forest - Post

Open - None

Open - RT

Open - RT & Post

Open - Post

Clackamas NetworkPro XR (Point Feature)

6 Meters

After 60

Positions

Accuracy Relative to Number of Positions

12

10

8

Meters 2dRMS

6

4

2

0

100

200

500

1000

1

2

5

10

20

50

Time in Seconds

Place - Corrections

clackamas network geoexplorer 3 point feature

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

Clackamas NetworkGeoExplorer 3 (Point Feature)

13 Meters

After 60

positions

Accuracy Relative to Number of Positions

40

35

30

25

20

Meters 2dRMS

15

10

5

0

100

200

500

1000

1

2

5

10

20

50

Time in Seconds

Place - Receiver - Corrections

what next
What Next?
  • NSSDA encourages agencies establish thresholds or data collection requirements for their product specifications and applications and for contracting purposes.
  • Data and map producers determine:
    • What accuracy exists
    • What accuracy is achievable
    • Then, report it according to NSSDA.
  • Data collection requirements are defined by the accuracy needed in the end product. The amount acceptable error is the “Error Budget”. Only data stewards or application managers can identify acceptable accuracies.
how a gps data standard may inform development of agency gps data collection requirements
How a GPS Data Standard may inform development of Agency GPS data collection requirements.
  • GIS or Application
  • Managers.

3. Agency Standards

2. NSSDA GPS Receiver Tests

slide41

Please send comments on thedraft standard to:Ken ChamberlainLand Surveyor BLM Oregon State Office Portland, Oregon503-808-6387http://www.fs.fed.us/database/gps/Ken_Chamberlain@or.blm.gov

national standard for spatial data accuracy42
National Standard for Spatial Data Accuracy

Citations and References

  • FGDC Standards, http://www.fgdc.gov/standards/standards.html
  • National Standard for Spatial Data Accuracy, http://www.fgdc.gov/standards/documents/standards/accuracy/chapter3.pdf
  • FGDC Digital Content Standard for Digital Geospatial Metadata, http://www.fgdc.gov/metadata/metadata.html
  • MrSID Accuracy Testing, http://www.lizardtech.com/crada/MrSIDacc2.html
  • Implementing the National Standard for Spatial Data Accuracy - Minnesota Governor's Council on Geographic Information, http://www.mnplan.state.mn.us/press/accurate.html
  • Test Driving the FGDC National Standard for Spatial Data Accuracy, by Donald Cooke and Mary Welsh, copyright ACSM 1998