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www.dewberry.com
Date:
January 29, 2010
Subject:
Report of Horizontal Accuracy Testing of Digital Orthophotos for PAMAP –
Montour County, Pennsylvania
Project Name:
Resolution:
State Plane Zone:
Production Block Reference:
Accepted/Rejected:
Production Company:
PAMAP
1 foot
Pennsylvania South NAD83
2008 Montour
Accepted
BAE
Counties in Production Block:
 Montour
References: a. FGDC Geospatial Positioning Accuracy Standards, Part 3: National Standard
for Spatial Data Accuracy (NSSDA)
b. PAMAP QAQC Work Plan.
Reference a. Published in 1998, the NSSDA implements a statistical and testing methodology
for estimating the positional accuracy of points on maps and in digital geospatial data, with
respect to georeferenced ground positions of higher accuracy, reported at the 95% confidence
level. The NSSDA replaces the 1947 National Map Accuracy Standard (NMAS) for digital
geospatial data. The NMAS is applicable to graphic maps, as accuracy is defined by map
scale. The NSSDA was developed to report accuracy of digital geospatial data that are not
constrained by scale, to include digital orthophotos.
Reference b. PAMAP 1’ digital orthophotos were tested in accordance with Acceptance Criteria
38 and 39 listed in Reference b. The “georeferenced ground positions of higher accuracy,”
referred to generically as “QA/QC checkpoints,” were provided by HRG. Each QA/QC
checkpoint is a ground point feature that is well-defined and photo-identifiable on the digital
orthophotos from which Pennsylvania State Plane South coordinates were measured by
Dewberry. Dewberry then determined the Δx and Δy differences in Eastings (x-coordinates) and
Northings (y-coordinates) between the ground-surveyed QA/QC checkpoints and their
coordinates extracted from the digital orthophotos. Dewberry then computed the root-meansquare-error (RMSE) statistics, including RMSEx, RMSEy, and RMSEr. RMSEr is the radial
statistic which equals the square root of [RMSEx2 + RMSEy2]. Finally, The NSSDA absolute
accuracy statistic (Accuracyr) is computed as RMSEr x 1.7308 in order to report the tested
horizontal accuracy at the 95% confidence level as required by Reference a.
Results:
Criteria for 12-inch GSD Imagery
RMSEx (acceptance criteria 38)
RMSEy (acceptance criteria 38)
RMSEr (acceptance criteria 38)
Accuracyr (acceptance criteria 39)
Acceptance Criteria
2.04 ft
2.04 ft
2.88 ft
5.00 ft
Tested
0.29 ft
0.64 ft
0.70 ft
1.21 ft
1
Horizontal Accuracy Testing of Digital Orthophotos for PAMAP
QA/QC Survey Checkpoints
Orthophoto Coordinates
Orthophoto minus
Discrepancies
Surveyed by HRG
Measured by Dewberry
surveyed coordinates
Squared as
Pennsylvania SPC South
Pennsylvania SPC South
NAD 83
NAD 83
required for
RMSE
calculations
Pennsylvania SPC South
NAVD 88
NAD 83
Point
Northing (y)
Easting (x)
Elevation (z)
Northing (y)
Easting (x)
Δy (Northing)
Δx (Easting)
Number
Feet
Feet
Feet
Feet
Feet
Feet
Feet
M-1H
342014.43
2268072.69
567.00
342014.76
2268072.36
0.33
M-2H
325494.37
2264800.15
515.30
325494.70
2264800.00
M-3Hv
291591.54
2292859.01
546.10
291592.54
2292858.68
Δy2 (ft2)
Δx2 (ft2)
-0.33
0.11
0.11
0.33
-0.15
0.11
0.02
1.00
-0.33
1.00
0.11
Sums
All coordinates in U.S. Survey Feet
Horizontal Accuracy Acceptance Criteria
RMSEx and RMSEy should be ≤ 2.04 ft
Threshold (ft)
RESULT:
5.000
PASS
RMSEr must be ≤ 2.88 ft
ACCURACYr must be ≤ 5.00 ft at 95% conf
level
MSE
RMSEyx (ft)
RMSEr (ft)
ACCURACYr
(ft)
1.22
0.24
0.41
0.08
0.64
per
NSSDA
per
NSSDA
0.29
0.70
1.21
2
Map Showing Distribution of QA Checkpoints
PAMAP – Montour County, PA
Tested 1.21 ft feet horizontal accuracy at 95% confidence level.
Approved by:
David F. Maune, Ph.D., PS, GS, CP
Project Manager
3