PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
January 2015
17
Table 3 Digital Orthoimagery Accuracy Examples for Current Large and
Medium Format Metric Cameras
Common
Orthoimagery
Pixel Sizes
Recommended
Horizontal
Accuracy Class
RMSE
x
and RMSE
y
(cm)
Orthoimage
RMSE
x
and
RMSE
y
in
terms of pixels
Recommended use
1.25 cm
≤1.3
≤1-pixel
Highest accuracy work
2.5
2-pixels
Standard Mapping and
GIS work
≥3.8
≥3-pixels
Visualization and less
accurate work
2.5 cm
≤2.5
≤1-pixel
Highest accuracy work
5.0
2-pixels
Standard Mapping and
GIS work
≥7.5
≥3-pixels
Visualization and less
accurate work
5 cm
≤5.0
≤1-pixel
Highest accuracy work
10.0
2-pixels
Standard Mapping and
GIS work
≥15.0
≥3-pixels
Visualization and less
accurate work
7.5 cm
≤7.5
≤1-pixel
Highest accuracy work
15.0
2-pixels
Standard Mapping and
GIS work
≥22.5
≥3-pixels
Visualization and less
accurate work
15 cm
≤15.0
≤1-pixel
Highest accuracy work
30.0
2-pixels
Standard Mapping and
GIS work
≥45.0
≥3-pixels
Visualization and less
accurate work
30 cm
≤30.0
≤1-pixel
Highest accuracy work
60.0
2-pixels
Standard Mapping and
GIS work
≥90.0
≥3-pixels
Visualization and less
accurate work
60 cm
≤60.0
≤1-pixel
Highest accuracy work
120.0
2-pixels
Standard Mapping and
GIS work
≥180.0
≥3-pixels
Visualization and less
accurate work
1 meter
≤100.0
≤1-pixel
Highest accuracy work
200.0
2-pixels
Standard Mapping and
GIS work
≥300.0
≥3-pixels
Visualization and less
accurate work
2 meter
≤200.0
≤1-pixel
Highest accuracy work
400.0
2-pixels
Standard Mapping and
GIS work
≥600.0
≥3-pixels
Visualization and less
accurate work
5 meter
≤500.0
≤1-pixel
Highest accuracy work
1,000.0
2-pixels
Standard Mapping and
GIS work
≥1,500.0
≥3-pixels
Visualization and less
accurate work
The standards also provide users with guidelines for
associating orthoimagery pixel sizes and associated RMSEx
and RMSEy accuracy, Table 3. As stated in the new standards,
the associating pixel size and products accuracy are largely
based on experience with current sensor technologies and
primarily apply to large and medium format metric cameras.
The table is only provided as a guideline for users during the
transition period to the new standards. These associations
may change in the future as mapping technologies continue to
advance and evolve.
The new standards also provide the following examples
to guide the user to relate the new standards to the legacy
standards. Such examples are important for the users to
prevent confusion and to assure a smooth transition to the
new standards.
Example 1: Converting the horizontal accuracy of a
map or orthoimagery from the new 2014 standards to
the legacy ASPRS map standards of 1990
Given:
a map or orthoimagery with an accuracy of RMSEx
= RMSEy = 15 cm according to the new 2014 standards,
compute the equivalent accuracy and map scale according to
the legacy ASPRS map standards of 1990, for the given map
or orthoimagery.
Solution:
1)
Because both standards utilize the same RMSE measure,
then the accuracy of the map according to the legacy ASPRS
map standards of 1990 is RMSEx = RMSEy = 15 cm
2)
To find the equivalent map scale according to the legacy
ASPRS map standards of 1990, follow the following steps:
a. Multiply the RMSEx and RMSEy value in centimeters
by 40 to compute the map scale
factor (MSF) for a Class 1 map, therefore:
MSF = 15 (cm) x 40 = 600
The map scale according to the legacy ASPRS map
standards of 1990 is equal to:
i. Scale = 1:MSF or 1:600 Class 1;
ii. The accuracy value of RMSEx = RMSEy = 15 cm is
also equivalent to Class 2 accuracy for a map with a
scale of 1:300.
(
to
be
continued
)
The contents of this column reflect the views of the author,
who is responsible for the facts and accuracy of the data pre-
sented herein. The contents do not necessarily reflect the offi-
cial views or policies of the American Society for Photogram-
metry and Remote Sensing and/or Woolpert, Inc.
“Many of the data acquisition and
mapping technologies that legacy
standards were based on are no longer
used in today’s mapping process.”
