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1

FGDC ACCURACY STANDARDS

NEW JERSEY SOCIETY OF PROFESSIONAL LAND SURVEYORS

ATLANTIC CITY

FEBRUARY 6, 2013

Dave Doyle

National Geodetic Survey (Retired)

[email protected]

Jesse Kozlowski

True Measure Consulting

[email protected]

mailto:[email protected]

2

POSITIONING ACCURACY STANDARDS

WORKSHOP OUTLINE

Introduction

Definitions

Evolution of Accuracy Standards

Classical Surveying Standards

GPS Surveying Standards

Development of New Accuracy Standard

Implementation of New Accuracy Standards

Guidelines & Procedures Documents

Computations/Software

Data Publications

Summary/Future

DEFINITIONS

DEFINITIONS

Survey Standards

Survey Specifications

Precision

Accuracy

WHAT IS A

SURVEY STANDARD?

WHAT IS A SURVEY STANDARD? (SOME PREVIOUS RESPONSES)

A level of precision of closure

A reasonably accepted error

A numerical limit on the uncertainty of

coordinates

Position relative to other points

Such as 0.1 (units) + X ppm

SURVEY STANDARDS

Survey standards may be defined as the

minimum accuracies deemed necessary to

meet specific objectives. (e.g. .1 ft, or

1/20,000)

For the present, the practice of defining these

criteria by the maximum acceptable

uncertainty in length and/or position and

assigning some nomenclature to them will be

continued.

WHY DO SURVEYORS NEED

ACCURACY STANDARDS?

WHY DO SURVEYORS NEED ACCURACY

STANDARDS? (SOME PREVIOUS RESPONSES)

To provide quality assurance of accuracy

Such as within 8 mm + 1 ppm; 5 cm; 0.5 m

To provide consistency

To re-establish survey monuments

SURVEY SPECIFICATIONS

Specifications can be described as the field

operations required to meet a particular survey

standard. (e.g. 1” theodolite, 8 positions D&R,

5 distances forward and back)

Also included are the specified precision and

allowable tolerances for the data collected, the

limitations of the geometric form of acceptable

figures, monumentation, and description of the

points.

DEFINITION OF PRECISION

Precision (1) In statistics, a measure of the tendency of

a set of random numbers to cluster about a number

determined by the set.

The usual measure is either the standard deviation with

respect to the average, or the reciprocal of the quantity. It is

distinguished from accuracy by the fact that the latter is a

measure of the tendency to cluster about a number not

determined by the set but specified in some other manner.

From: Geodetic Glossary, National Geodetic Survey,

September 1986

STANDARD ERROR OF THE MEAN

m =

v2

n (n - 1)

Where m is the standard error

of the mean, v is a residual (that is,

the difference between a measured

length and the mean of all measured

lengths of a line), and n is the number

of measurements.

The term “standard error” used here is computed under the assumption

that all errors are strictly random in nature. The true or actual error is a

quantity that cannot be obtained exactly. It is the difference between the

true value and the measured value. By correcting each measurement for

every known source of systematic error, however, one may approach the

true error. It is mandatory for any practitioner using these tables to

reduce to a minimum the effect of all systematic and constant errors so

that real accuracy may be obtained.

STANDARD DEVIATION

s =

v2

n - 1

Where s is the standard deviation,

v is a residual (that is, the difference

between a measured length and the mean

of all measured lengths of a line), and n

is the number of measurements.

= sigma or 1 standard deviation

= 68.3% certainty

2 = 2 sigma or 2 standard deviations

= 95.0% certainty

Which would you pick, 1 or 2 sigma??

accuracy (1) Closeness of an estimated (e.g., measured or

computed) value to a standard or accepted value of a particular quantity.

Accuracy is commonly referred to as “high” or “low” depending on the size of

the differences between the estimated and the standard values.

(2) The square root of the average value of the sum of the squares of the

differences between the values in a set and the corresponding values that

have been accepted as correct or standard.

(3) The reciprocal of the quantity defined in (2).

Accuracy cannot be calculated solely from values based on measurements. A

standard value or set of standard values must be available for comparison

somewhere in the chain of calculations. The standard of reference may be:

(a) an exact value, such as the sum of the three angles of a plane triangle

being exactly 180°; (b) a value of a conventional unit as defined by a physical

representation thereof, such as the international meter; (c) a value

determined by refined methods and deemed sufficiently near the ideal or true

value to be held constant, such as the adjusted elevation of a permanent

bench mark or the graticule of a map projection.

From: Geodetic Glossary, National Geodetic Survey, September 1986

DEFINITION OF ACCURACY

CLOSURE

Is it a Standard

or

is it a Specification?

EXAMPLES OF CLOSURE

A B

B'

C

C'

D

D'

Starting

Azimuth Accurate Survey

Survey with

starting azimuth

error and systematic

distance error

Note that both surveys

produce excellent

closures - Regrettably the

vast majority of older

surveys exhibit this

condition

WHAT DOES FIRST-ORDER HORIZONTAL

ACCURACY MEAN?

JONES to SMITH = 45,230 feet

Therefore, the accuracy of the relationship between

JONES and SMITH is:

45,230/100,000 = 0.452 feet

JONES

SMITH

19

20 PERCENT RULE

Whenever the distance between two

new unconnected survey points is less than

20 percent of the distance between those

points traced along existing or new

connections, then a direct connection must

be made between those two survey points.

TYPES OF FIGURES WHERE IT MAY BE DIFFICULT TO

OBTAIN SATISFACTORY CLOSURES

WIPPER

(USGS)

PETERSON

FRANKLIN

(USGS)

HAFNER

MT PLEASANT

SNOW PEAK

LARCH

SQUAW

ZIGZAG

MT HOOD

CHINIDERE 2

Surveys between MT PLEASANT-

FRANKLIN (USGS) and MT HOOD-

ZIGZAG might not close to minimum

stated standards of points involved.

WHAT DOES FIRST-ORDER HORIZONTAL ACCURACY MEAN? (WHEN THE POINTS AREN’T DIRECTLY CONNECTED)

JONES

GEAN

SMITH

JONES to SMITH = 45,230 feet

JONES to GEAN = 37,467 feet

SMITH to GEAN* = 15,502 feet (* not observed)

The accuracy of the relationship between SMITH

and GEAN is:

√[(0.452)2 + (0.375)2] = 0.587 feet

NOT 15,502 /100,000 = 0.155 feet

ACCURACY STANDARDS FOR VERTICAL CONTROL

(K is the distance in kilometers between points)

Relative Accuracy

Between Directly

Connected Points

or Bench Marks

Classification (Standard Error)

First - Order, Class I 0.5 mm √K

First - Order, Class II 0.7 mm √K

Second - Order, Class I 1.0 mm √K

Second - Order, Class II 1.3 mm √√K

Third - Order 2.0 mm √K

WHAT DOES FIRST-ORDER, CLASS II

ACCURACY MEAN?

D 236 E 236

F 236 G 236

H 236

D 236 to G 236 = 3 miles = 4.8 km

Therefore, the accuracy of the vertical relationship

between D 236 and G 236 is:

0.7 √4.8 = 1.5 mm

24 WHAT DOES SECOND-ORDER, CLASS I ACCURACY MEAN?

(WHEN THE POINTS AREN’T DIRECTLY CONNECTED.)

D 236 to R 78 = 7 miles = 11.2 km

D 236

F 236 G 236

H 236

E 236

R 78 S 78

T 78 U 78

V 78

Therefore, the accuracy of the vertical relationship between

D 236 and R 78 is:

1.0 √ 11.2 = 3.3 mm

NOT: 1.0 √1.6 = 1.3 mm

25

EVOLUTION OF ACCURACY

STANDARDS

NATIONAL STANDARDS FOR HORIZONTAL AND

VERTICAL POSITIONING

Prior to 1921

Primary, Secondary, Tertiary

(No specific positional integrity defined)

(General Instructions for the Field Work of the USC&GS)

After 1921

Precise, Primary and Secondary

(Same as previous – not well accepted)

May 25, 1925

Board of Surveys and Maps of the Federal Government

1st, 2nd and 3rd – Orders adopted

1925

Horizontal (Relative accuracy between directly connected points)

1st- Order = 1:25,000

2nd- Order = 1:10,000

3rd- Order = 1:5,000

Vertical 1st- Order = 4 mm (0.017 ft) * √ k (k = length of section in km)

2nd- Order = 8.4 mm (0.035 ft)* √ k

3rd- Order = 12 mm (0.05 ft) * √ k



Special Publication 120

Special Publication 145

1925

Horizontal No instrumentation specifications defined (e.g. 1” theodolite etc.). Only general

specifications “direction instruments of the highest grade should be used …”

Average triangle closure should seldom exceed 1”

Difference between measured and computed baseline not to exceed 1:25,000

Vertical 1st- Order = 4 mm (0.017 ft) * √ k (k = length of section in km – typically 1-2 km)

2nd- Order = 8.4 mm (0.035 ft)* √ k

3rd- Order = 12 mm (0.05 ft) * √ k



March 1, 1957 – Office of Management and Budget, Circular A-16, Exhibit C Rational for changes in horizontal standards due primarily to significant developments in

Electronic Distance Measuring Equipment (EDM) (e.g. Geodimeter, Tellurometer)


1st- Order Class I = 1:100,000

1st- Order Class II = 1:50,000

1st- Order Class III = 1:25,000

2nd- Order Class I = 1:20,000

2nd- Order Class II = 1:10,000

3rd- Order = 1:5,000

Vertical (Section closures)

1st- Order Class I = 3 mm* √ k

1st- Order Class II = 4 mm* √ k

2nd- Order Class I = 6 mm * √ k

2nd- Order Class II = 8 mm* √ k

3rd- Order vertical = 12 mm* √ k



33

CLASSIFICATION OF CONTROL

The foregoing data concerning control classification may be tabulated as follows:

Special Publication No. 247

Manual of Geodetic Triangulation (1950)

First Order Second Order Third Order Fourth Order

Triangulation …...

Traverse ………...

Leveling …………

Average triangle clo-

sure 1”, check on

base 1/25,000.

Position check

1/25,000.

Error of closure of

section 0.017 ft.

miles or 4 mm.

kilometers.


sure 3”, check on

base 1/10,000.

Position check

1/10,000.

Error of closure of

section 0.035 ft.

miles or 8.4 mm.

kilometers.


sure 5”, check on

base 1/5,000.

Position check

1/5,000.

Error of closure of

section 0.05 ft.

miles or 12 mm.

kilometers.

Plane table or transit.

Stadia, tape, or wheel.

Flying wye levels, ver-

tical angles.

1974 Creation of Federal Geodetic Control Committee

(FGCC) – Chaired by Director, National Geodetic Survey

Publications:

“Standards of Accuracy and General Specifications of Geodetic Control Surveys”

“Specifications to Support Classification, Standards and Accuracy, and General

Specifications of Geodetic Control Surveys”

Minor changes in horizontal standards and more rigorous specifications (you must do)

adopted.



1974 – Federal Geodetic Control Committee


1st- Order Class = 1:100,000

2nd- Order Class I = 1:50,000

2nd- Order Class II = 1:20,000

3rd- Order Class I = 1:10,000

3rd- Order Class II = 1:5,000

Vertical (Relative accuracy between directly connected points)

1st- Order Class I = 3 mm* √ k

1st- Order Class II = 4 mm* √ k

2nd- Order Class I = 6 mm* √ k

2nd- Order Class II = 8 mm* √ k

3rd- Order vertical =12 mm* √ k

NATIONAL STANDARDS FOR HORIZONTAL AND VERTICAL

POSITIONING

1974 Examples

Horizontal Instrumentation specifications rigorously defined

1st – Order = 0.2” theodolite

16 positions D&R

Baseline Standard Error = 1: 1,000,000

2nd – Order Class II = 0.2” or 1.0” theodolite

8 positions D& R for 0.2”

12 positions D&R for 1.0”

Baseline Standard Error = 1: 800,000



1974 Continued

Vertical Instrumentation specifications rigorously defined

1st – Order Class II= Automatic or tilting level with parallel plate micrometers and invar scale rods

Temperature compensated

Bubble sensitivity = 0.25 seconds of arc

Gravity requirement = 0.2 x 10-3gpu (geopotential unit)

Maximum line of sight = 60 m

2nd – Order Class II = Three-wire Geodetic levels with invar scale rods

Temperature not required

Bubble sensitivity = 0.5 seconds of arc

Maximum line of sight = 70 m



1984 FGCC Updates Standards and Specifications

“Standards and Specifications of Geodetic Control Networks” http://www.ngs.noaa.gov/FGCS/tech_pub/1984-stds-specs-geodetic-control-networks.htm



1989 FGCC publishes first GPS Standards and

Specifications’

“Geometric Geodetic Accuracy Standards and Specifications for using

GPS Relative Positioning Techniques”

New orders of accuracy created:

AA –Order -- (1:100,000,000)

A-Order -- (1:10,000,000)

B-Order -- (1:1, 000,000)

GPS technology changes so rapidly that this document never went beyond

“Draft”



October 1990 – Office of Management and Budget

(OMB) creates the Federal Geographic Data

Committee (FGDC) -- 19 member interagency committee

composed of representatives from the Executive Office of the

President, Cabinet-level and independent agencies.



FGCC becomes Federal Geodetic Control

Subcommittee (FGCS) under FGDC – still chaired

by the Director, National Geodetic Survey

1988

Geometric Geodetic Accuracy Standards and

Specifications for Using GPS Relative Techniques http://www.ngs.noaa.gov/FGCS/tech_pub/GeomGeod.pdf



Established new horizontal positioning standards

that never existed before: A-Order 1:10,000,000

B-Order 1;1,000,000

Never formally adopted by FGCS – GPS technology changed too fast!

1998

FGDC/FGCS adopts

Geospatial Positioning Accuracy Standards

FGDC-STD-007.2-1998

http://www.fgdc.gov/standards/projects/FGDC-standards-projects/accuracy/part2/chapter2

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 meter

2-Millimeter 0.002 “

5-Millimeter 0.005 "

1-Centimeter 0.010 "



1-Decimeter 0.100 "



Only sort of implemented – kind of!!

Horizontal and Ellipsoid Height (NAD 83) – Not Orthometric Height (NAVD 88)


VERTICAL POSITIONING National Geodetic Survey, Retrieval Date = DECEMBER 19, 2012

JU0320 ***********************************************************************

JU0320 DESIGNATION - LIGHTHOUSE PARK

JU0320 PID - JU0320

JU0320 STATE/COUNTY- NJ/ATLANTIC

JU0320 COUNTRY - US

JU0320 USGS QUAD - ATLANTIC CITY (1994)

JU0320

JU0320 *CURRENT SURVEY CONTROL

JU0320 ______________________________________________________________________

JU0320* NAD 83(2011) POSITION- 39 21 57.91963(N) 074 24 49.63659(W) ADJUSTED

JU0320* NAD 83(2011) ELLIP HT- -32.537 (meters) (06/27/12) ADJUSTED

JU0320* NAD 83(2011) EPOCH - 2010.00

JU0320* NAVD 88 ORTHO HEIGHT - 1.874 (meters) 6.15 (feet) ADJUSTED

JU0320 ______________________________________________________________________

JU0320 NAD 83(2011) X - 1,326,680.507 (meters) COMP

JU0320 NAD 83(2011) Y - -4,756,054.105 (meters) COMP

JU0320 NAD 83(2011) Z - 4,023,799.847 (meters) COMP

JU0320 LAPLACE CORR - -2.25 (seconds) DEFLEC12A

JU0320 GEOID HEIGHT - -34.43 (meters) GEOID12A

JU0320 DYNAMIC HEIGHT - 1.873 (meters) 6.15 (feet) COMP

JU0320 MODELED GRAVITY - 980,106.8 (mgal) NAVD 88

JU0320

JU0320 VERT ORDER - FIRST CLASS I

JU0320

JU0320 FGDC Geospatial Positioning Accuracy Standards (95% confidence, cm)

JU0320 Type Horiz Ellip Dist(km)

JU0320 -------------------------------------------------------------------

JU0320 NETWORK 0.94 1.39

JU0320 -------------------------------------------------------------------

JU0320 MEDIAN LOCAL ACCURACY AND DIST (005 points) 0.93 1.33 2.21

JU0320 -------------------------------------------------------------------

JU0320 NOTE: Click here for information on individual local accuracy

JU0320 values and other accuracy information.

JU0320

JU0320

JU0320.The horizontal coordinates were established by GPS observations

JU0320.and adjusted by the National Geodetic Survey in June 2012.

JU0320

JU0320.NAD 83(2011) refers to NAD 83 coordinates where the reference

JU0320.frame has been affixed to the stable North American tectonic plate. See

JU0320.NA2011 for more information. for more information.

JU0320

JU0320.The horizontal coordinates are valid at the epoch date displayed above

JU0320.which is a decimal equivalence of Year/Month/Day.


VERTICAL POSITIONING JU0320; North East Units Scale Factor Converg.

JU0320;SPC NJ - 59,142.748 157,428.861 MT 0.99990068 +0 03 16.9

JU0320;SPC NJ - 194,037.50 516,497.85 sFT 0.99990068 +0 03 16.9

JU0320;UTM 18 - 4,357,566.986 550,498.688 MT 0.99963140 +0 22 18.6

JU0320

JU0320! - Elev Factor x Scale Factor = Combined Factor

JU0320!SPC NJ - 1.00000510 x 0.99990068 = 0.99990578

JU0320!UTM 18 - 1.00000510 x 0.99963140 = 0.99963650

JU0320

JU0320: Primary Azimuth Mark Grid Az

JU0320:SPC NJ - RITZ 240 13 44.3

JU0320:UTM 18 - RITZ 239 54 42.6

JU0320

JU0320|---------------------------------------------------------------------|

JU0320| PID Reference Object Distance Geod. Az |

JU0320| dddmmss.s |

JU0320| JU2780 BRIGANTINE BEACH SOUTH TANK APPROX. 3.8 KM 0313051.0 |

JU0320| JU0321 LIGHTHOUSE PARK RM 1 36.890 METERS 05324 |

JU0320| CB2181 LIGHTHOUSE PARK RM 3 23557 |

JU0320| JU2765 ATLANTIC CITY CLARIDGE HOTEL APPROX. 1.8 KM 2383036.2 |

JU0320| JU2778 RITZ APPROX. 3.0 KM 2401701.2 |

JU0320| JU2779 ATLANTIC CITY RADIO WFPG MAST APPROX. 3.5 KM 2891617.0 |

JU0320| JU2770 ATLANTIC CITY MUNICIPAL TANK APPROX. 1.2 KM 2943015.1 |

JU0320| JU2772 ABSECON LIGHT 40.031 METERS 31045 |

JU0320| JU2771 BASIC BENCH MARK 1962 52.760 METERS 31746 |

JU0320|---------------------------------------------------------------------|

JU0320

JU0320 SUPERSEDED SURVEY CONTROL

JU0320

JU0320 NAD 83(2007)- 39 21 57.92001(N) 074 24 49.63736(W) AD( ) 0

JU0320 ELLIP H (02/10/07) -32.527 (m) GP( )

JU0320 ELLIP H (10/23/02) -32.498 (m) GP( ) 4 1

JU0320 NAD 83(1996)- 39 21 57.91974(N) 074 24 49.63728(W) AD( ) 1

JU0320 ELLIP H (05/14/99) -32.516 (m) GP( ) 4 1

JU0320 NAD 83(1986)- 39 21 57.91821(N) 074 24 49.63604(W) AD( ) 1

JU0320 ELLIP H (03/31/93) -32.580 (m) GP( ) 3 2

JU0320 NAD 83(1986)- 39 21 57.90902(N) 074 24 49.62921(W) AD( ) 3

JU0320 NAD 27 - 39 21 57.48690(N) 074 24 51.10000(W) AD( ) 3

JU0320 NAVD 88 (03/31/93) 1.87 (m) 6.1 (f) LEVELING 3

JU0320 NGVD 29 (01/10/92) 2.279 (m) 7.48 (f) ADJUSTED 1 1

First-Order

Fourth-Order