Accuracy Standards used for Mapping Projects in North Carolina

1
North Carolina Department of TransportationPhotog
rammetry Unit

• Accuracy Standards used for Mapping Projects in
  North Carolina
• May 5, 2005
• NCASPRS Spring Conference

2
North Carolina Department of TransportationPhotog
rammetry UnitPresentation Outline

• Requirement for Accuracy Standards
• Common Accuracy Standards
• Statistics Formulas Associated with Accuracy
  Standards
• Test Case Application of the Accuracy Standards
  to Real Data

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North Carolina Department of TransportationPhotog
rammetry UnitRequirement for Accuracy Standards

• North Carolina Board of Examiners for Engineers
  and Surveyors (NCBELS) - NC Administrative Code
  (Title 21, Chapter 56)
• http//www.ncbels.org/chapter21.pdf
• North Carolina Geographic Information
  Coordinating Council (NC GICC) Digital Orthophoto
  Standard
• http//www.cgia.state.nc.us/gicc/standards/orthost
  and.pdf
• NCDOT Contractual Map Accuracy Specifications

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North Carolina Department of TransportationPhotog
rammetry UnitRequirement for Accuracy Standards

• NCBELS - NC Administrative Code Section
  21-56.1606(c) states

Topographic or planimetric maps, orthophotos,
and/or related electronic data, unless clearly
marked as Preliminary Map, shall meet
contractually specified FGDC Standards for
horizontal and vertical accuracies (in the
absence of specified standards, the National Map
Accuracy Standards apply) and shall be sealed,
signed and dated by the licensee.
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North Carolina Department of TransportationPhotog
rammetry UnitRequirement for Accuracy Standards

• NC GICC Digital Orthophoto Standard states

Orthophotos shall meet the ASPRS Class II
horizontal accuracy standards as
follows Orthophoto Scale ASPRS Limiting RMSE
in X or Y (Class II) 1400 8.0 1200 4.0
1100 2.0 150 1.0
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North Carolina Department of TransportationPhotog
rammetry UnitRequirement for Accuracy Standards

• NCDOT Limited Services Agreement, Section I.D
  states

All topographic and planimetric maps, digital
orthophotography, base plan sheets, and digital
map or base plan sheet data shall comply with
National Map Accuracy Standards as outlined in
the Reference Guide Outline Specifications for
Aerial Surveys and Mapping, published by the U.S.
Department of Transportation.
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North Carolina Department of TransportationPhotog
rammetry Unit Common Accuracy Standards

• FGDC-STD-007-1998 (1998)
• http//www.fgdc.gov/standards/documents/standards/
  accuracy/chapter3.pdf
• ASPRS Accuracy Standards for Large-Scale Maps
  (1990)
• http//www.asprs.org/resources/standards.html
• USDOT Reference Guide Outline - Specifications
  for Aerial Surveys and Mapping by Photogrammetric
  Methods for Highways (1968)
• http//www.fhwa.dot.gov/legsregs/directives/fapg/g
  601205.htm
• National Map Accuracy Standards (1947)
• http//rockyweb.cr.usgs.gov/nmpstds/nmas647.html

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North Carolina Department of TransportationPhotog
rammetry Unit Common Accuracy Standards

• FGDC-STD-007-1998 (1998)
• Independent of Map Scale and Contour Interval
• Accuracy Reporting at 95 confidence level and is
  based on either Testing or Procedure
• Accuracy Reporting (Testing)

Tested ____ (meters, feet) horizontal accuracy at
95 confidence level Tested ____ (meters, feet)
vertical accuracy at 95 confidence level

• Accuracy Reporting (Procedure)

Compiled to meet ___ (meters, feet) horizontal
accuracy at 95 confidence level Compiled to meet
___(meters, feet) vertical accuracy at 95
confidence level
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North Carolina Department of TransportationPhotog
rammetry Unit Common Accuracy Standards

• ASPRS Accuracy Standards for Large-Scale Maps
  (1990)
• Dependent on Map Scale and Contour Interval
• Accuracy Reporting at RMSE (1s or 68.3
  confidence) level and is based on either Testing
  or Procedure
• Accuracy Reporting (Testing)

THIS MAP WAS CHECKED AND FOUND TO CONFORM TO THE
ASPRS STANDARD FOR CLASS 1 MAP ACCURACY.

• Accuracy Reporting (Procedure)

THIS MAP WAS COMPILED TO MEET THE ASPRS STANDARD
FOR CLASS 1 MAP ACCURACY.
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North Carolina Department of TransportationPhotog
rammetry Unit Common Accuracy Standards

• ASPRS Accuracy Standards for Large-Scale Maps
  (1990)
• Class 1 Horizontal Accuracy Standard (typical
  scales)

Map Scale Limiting RMSE in X or
Y 1400 4.00 1200 2.00 1100 1.00
150 0.50

• Class 1 Vertical Accuracy Standard (typical
  contour intervals)
• for contours - limiting RMSE Z is 1/3 the
  contour interval
• for spot elevations - limiting RMSE Z is 1/6 the
  contour interval

Contour Interval Limiting RMSE Z
(contours) Limiting RMSE Z (spots) 5 1.67 0.8
3 4 1.33 0.67 2 0.67 0.33 1 0.33
0.17
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North Carolina Department of TransportationPhotog
rammetry Unit Common Accuracy Standards

• USDOT Reference Guide Outline(1968)
• Dependent on Map Scale and Contour Interval
• Accuracy Reporting language not explicitly
  defined
• Accuracy Requirements at 90 confidence level
• Horizontal Accuracy
• 90 of planimetric features are within 1/40 at
  map scale
• Vertical Accuracy
• 90 of elevations determined from contours are
  within 1/2 contour interval
• 90 of spot elevations are within 1/4 contour
  interval

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North Carolina Department of TransportationPhotog
rammetry Unit Common Accuracy Standards

• USDOT Reference Guide Outline(1968)
• Horizontal Accuracy Standard (typical scales)

Map Scale Radial Accuracy at 90 confidence
level 1400 10.00 1200 5.00 1100 2
.50 150 1.25

• Vertical Accuracy Standard (typical contour
  intervals)

Contour Interval Accuracy _at_ 90 (contours)
Accuracy _at_ 90 (spots) 5 2.50 1.25 4 2.00
1.00 2 1.00 0.50 1 0.50 0.25
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North Carolina Department of TransportationPhotog
rammetry Unit Common Accuracy Standards

• National Map Accuracy Standards (1947)
• Its really applicable to small scale mapping
• Dependent on Map Scale and Contour Interval
• Accuracy Reporting
• This map complies with National Map accuracy
  standards.
• Accuracy Requirements at 90 confidence level
• Horizontal Accuracy
• 90 of planimetric features are within 1/30 at
  map scale for map scales larger than 120,000
• Vertical Accuracy
• 90 of elevations determined from contours are
  within 1/2 contour interval

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North Carolina Department of TransportationPhotog
rammetry Unit Common Accuracy Standards

• National Map Accuracy Standards (1947)
• Horizontal Accuracy Standard (typical scales)

Map Scale Radial Accuracy at 90 confidence
level 1400 13.33 1200 6.67 1100 3
.33 150 1.67

• Vertical Accuracy Standard (typical contour
  intervals)

Contour Interval Accuracy _at_ 90
(contours) 5 2.50 4 2.00 2 1.00
1 0.50
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North Carolina Department of TransportationPhotog
rammetry Unit Statistics Formulas Associated
with Accuracy Standards

• Normal Distribution Function - A mathematical
  function describing the behavior of
  one-dimensional random errors whose graph is a
  bell-shaped curve that extends indefinitely in
  both directions.

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North Carolina Department of TransportationPhotog
rammetry Unit Statistics Formulas Associated
with Accuracy Standards
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North Carolina Department of TransportationPhotog
rammetry Unit Statistics Formulas Associated
with Accuracy Standards

• Confidence Level and the Bell Shaped Curve
• 1 sigma (1s) level equals 68.26 of area under
  the curve
• 2 sigma (2s) level equals 95.44 of area under
  the curve
• 3 sigma (3s) level equals 99.74 of area under
  the curve

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North Carolina Department of TransportationPhotog
rammetry UnitStatistics Formulas Associated
with Accuracy Standards

• Utilizes well defined independent checkpoints
  (differences between higher order surveyed
  coordinates and product test coordinates are
  calculated for each checkpoint component)

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North Carolina Department of TransportationPhotog
rammetry Unit Statistics Formulas Associated
with Accuracy Standards

• ASPRS Accuracy Standards for Large-Scale Maps
  (1990)
• based on 1s (68.3 ) confidence level
• Horizontal Accuracy - uses RMSE X and Y values
• Vertical Accuracy - uses RMSE Z value

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North Carolina Department of TransportationPhotog
rammetry Unit Statistics Formulas Associated
with Accuracy Standards

• FGDC-STD-007-1998 (1998) - based on 95
  confidence level
• Horizontal Accuracy - 2 cases dependent on RMSE X
  and Y values

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North Carolina Department of TransportationPhotog
rammetry Unit Statistics Formulas Associated
with Accuracy Standards

• FGDC-STD-007-1998 (1998) - based on 95
  confidence level
• Horizontal Accuracy - 2 cases dependent on RMSE X
  and Y values

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North Carolina Department of TransportationPhotog
rammetry Unit Statistics Formulas Associated
with Accuracy Standards

• FGDC-STD-007-1998 (1998) - based on 95
  confidence level
• Vertical Accuracy

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North Carolina Department of TransportationPhotog
rammetry Unit Statistics Formulas Associated
with Accuracy Standards

• National Map Accuracy Standards (1947) - 90
  confidence level
• Horizontal Accuracy

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North Carolina Department of TransportationPhotog
rammetry Unit Statistics Formulas Associated
with Accuracy Standards

• National Map Accuracy Standards (1947) - 90
  confidence level
• Vertical Accuracy

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North Carolina Department of TransportationPhotog
rammetry Unit Statistics Formulas Associated
with Accuracy Standards

• USDOT Reference Guide Outline(1968) - 90
  confidence level
• Horizontal Accuracy - same formula as NMAS
• Vertical Accuracy - same formula as NMAS

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North Carolina Department of TransportationPhotog
rammetry UnitTest Case Application of the
Accuracy Standards to Real Data
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North Carolina Department of TransportationPhotog
rammetry Unit Test Case Application of the
Accuracy Standards to Real Data

• ASPRS Accuracy Standards for Large-Scale Maps
  (1990)
• RMSE X 0.72 ft RMSE Y 0.95 ft RMSE Z 1.01
  ft
• Horizontal Accuracy - Class 1 Map Accuracy for
  1100 scale
• Vertical Accuracy
• Contours - would support a 3.03 ft contour
  interval
• Spots - would support a 6.06 ft contour interval

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North Carolina Department of TransportationPhotog
rammetry Unit Test Case Application of the
Accuracy Standards to Real Data

• FGDC-STD-007-1998 (1998)
• RMSE X 0.72 ft RMSE Y 0.95 ft RMSE Z 1.01
  ft
• RMSE X does not equal RMSE Y - therefore, use
  Case 2 formula
• Approximate Horizontal Accuracy (radial) 2.04
  ft
• Vertical Accuracy (95 confidence) 1.99 ft

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North Carolina Department of TransportationPhotog
rammetry Unit Test Case Application of the
Accuracy Standards to Real Data

• National Map Accuracy Standards (1947)
• RMSE X 0.72 ft RMSE Y 0.95 ft RMSE Z 1.01
  ft
• RMSE X does not equal RMSE Y - guidance not
  provided in the standard for this case
• therefore, use Case 2 formula from FGDC standard
  substituting the 90 factor value of 2.146 for
  2.4477
• Approximate Horizontal Accuracy (radial) 1.79
  ft
• may support a 153.7 map scale
• Vertical Accuracy (90 confidence) 1.67 ft
• Contours - would support a 3.34 ft contour
  interval

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North Carolina Department of TransportationPhotog
rammetry Unit Test Case Application of the
Accuracy Standards to Real Data

• USDOT Reference Guide Outline(1968)
• RMSE X 0.72 ft RMSE Y 0.95 ft RMSE Z 1.01
  ft
• RMSE X does not equal RMSE Y - guidance not
  provided in the standard for this case
• therefore, use Case 2 formula from FGDC standard
  substituting the 90 factor value of 2.146 for
  2.4477
• Approximate Horizontal Accuracy (radial) 1.79
  ft
• may support a 171.6 map scale
• Vertical Accuracy (90 confidence) 1.67 ft
• Contours - would support a 3.34 ft contour
  interval
• Spots - would support a 6.68 ft contour interval

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North Carolina Department of TransportationPhotog
rammetry UnitTest Case Application of the
Accuracy Standards to Real Data
Horizontal Accuracy (radial) - does not follow
normal distribution
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North Carolina Department of TransportationPhotog
rammetry UnitTest Case Application of the
Accuracy Standards to Real Data
Vertical Accuracy - does not follow normal
distribution
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North Carolina Department of TransportationPhotog
rammetry Unit Test Case Application of the
Accuracy Standards to Real Data

• Summary
• RMSE X 0.72 ft RMSE Y 0.95 ft RMSE Z 1.01 ft

Approximate Horizontal Accuracy By Case 2
Formula By Sample Radial Accuracy at 95
confidence 2.04 ft 2.12 ft Radial Accuracy at
90 confidence 1.79 ft 1.96 ft
Approximate Vertical Accuracy By Formula By
Sample Vertical Accuracy at 95 confidence 1.99
ft 2.14 ft Vertical Accuracy at 90
confidence 1.56 ft 1.67 ft
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North Carolina Department of TransportationPhotog
rammetry Unit Test Case Application of the
Accuracy Standards to Real Data

• Summary
• RMSE X 0.72 ft RMSE Y 0.95 ft RMSE Z 1.01
  ft
• ASPRS - Class 1 map at 1100, 3 - 6 ft contour
  interval depending on requirement for spot
  elevations
• FGDC - 2.2 ft approximate horizontal accuracy
  (radial) at 95 confidence, 2.2 ft approximate
  vertical accuracy at 95 confidence
• NMAS - 2.0 ft approximate horizontal accuracy
  (radial) at 90 confidence, 1.7 ft approximate
  vertical accuracy at 90 confidence, 160 map
  scale, 4 - 8 ft contour interval depending on
  requirement for spot elevations
• USDOT - 2.0 ft approximate horizontal accuracy
  (radial) at 90 confidence, 1.7 ft approximate
  vertical accuracy at 90 confidence, 180 map
  scale, 4 - 8 ft contour interval depending on
  requirement for spot elevations