16
January 2015
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
The new standards bring new and improved approaches
in dealing with current mapping products. It also provides a
wealth of information and measures for the users to utilize
that were never introduced by the legacy standards. Among
such improvements are the following:
1.
Providing unlimited number of horizontal and vertical
accuracy classes that can accommodate products from
any of the current or future mapping technologies.
2.
Dealing with LiDAR and other modern technologies.
3.
Utilizing positional accuracy thresholds for digital
orthoimagery and digital elevation data that are
independent of published GSD, map scale or contour
interval.
4.
Providing aerial triangulation accuracy measure.
5.
Providing ground controls accuracy measure.
6.
Providing orthoimagery seam lines accuracy measure.
7.
Providing lidar relative swath-to-swath accuracy
measure for LiDAR and IFSAR data.
8.
Providing recommended minimum Nominal Pulse
Density (NPD) for LiDAR data.
9.
Providing horizontal accuracy measure for elevation
data,
10.
Providing definitions and guidelines for the delineation
of low confidence areas for elevation data.
11.
Providing guidelines on the required number and spatial
distribution of QA/QC check points based on project area.
12.
Providing methodology for reporting products accuracy.
13.
Providing definitions of statistical terms that are related
to accuracy computations and provide practical examples
on its use.
14.
Providing tutorial sections with practical examples on
relating the new standards to the legacy standards.
In the following sections I will try to introduce the structure
of the accuracy classes and the newly introduced sections of
the new standards.
H
orizontal
A
ccuracy
S
tandards
for
G
eospatial
D
ata
The new standards defines horizontal accuracy classes in
terms of the value of errors presented in data represented by
the Root Mean Square (RMSE). Such accuracy class definition
do not limit the classes to a certain ranking or certain number
of classes as the legacy standards did. This approach offers
many advantages and flexibility for the users of the standards
as it assigns an accuracy class for any product from any
current or future technologies. Table 1 provides the horizontal
accuracy classes for geospatial data.
Based on Table 1, data users, when they request products
such as digital orthoimagery or digital planimetric data, can
specify that the datamust be produced tomeet ASPRSAccuracy
Standards for the RMSEx and RMSEy Horizontal Accuracy
Class he or she is interested in. If 10 cm accuracy is desired,
then the statement can be written as “the data set should
be produced to meet ASPRS Positional Accuracy Standards
for Digital Geospatial Data (2014) for 10.0 (cm) RMSEx and
RMSEy Horizontal Accuracy Class”. The standards, Table
2, lists 24 common accuracy classes for orthoimagery and
planimetric maps.
“the new standards are published to
meet the dire needs of new era for the
geospatial community.”
Table 1 Horizontal Accuracy Standard for Geospatial Data
Horizontal
Accuracy Class
Absolute Accuracy
Relative Accuracy Measures
RMSE
x
and RMSE
y
cm)
RMSEr
(cm)
Horizontal Accuracy at 95% Confidence Level
(cm)
Orthoimagery Mosaic Seamline Mismatch
(cm)
X-cm
≤X
≤1.41*X
≤2.45*X
≤ 2*X
Table 2 Common Horizontal Accuracy Classes according to the new
standards
Horizontal Accuracy
Class RMSE
x
and
RMSE
y
(cm)
RMSE
r
(cm)
Orthoimage Mosaic
Seamline Maximum
Mismatch (cm)
Horizontal Accuracy
at the 95% Confidence
Level (cm)
0.63
0.9
1.3
1.5
1.25
1.8
2.5
3.1
2.50
3.5
5.0
6.1
5.00
7.1
10.0
12.2
7.50
10.6
15.0
18.4
10.00
14.1
20.0
24.5
12.50
17.7
25.0
30.6
15.00
21.2
30.0
36.7
17.50
24.7
35.0
42.8
20.00
28.3
40.0
49.0
22.50
31.8
45.0
55.1
25.00
35.4
50.0
61.2
27.50
38.9
55.0
67.3
30.00
42.4
60.0
73.4
45.00
63.6
90.0
110.1
60.00
84.9
120.0
146.9
75.00
106.1
150.0
183.6
100.00
141.4
200.0
244.8
150.00
212.1
300.0
367.2
200.00
282.8
400.0
489.5
250.00
353.6
500.0
611.9
300.00
424.3
600.0
734.3
500.00
707.1
1000.0
1223.9
1000.00
1414.2
2000.0
2447.7
