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Geo-referenced ortho-rectified imagery provide
photographic information registered to geodetic
models to support compilation
of planimetric mapping themes.
The ortho-rectification process
can correct various sources of
geo-registration error.
Earth-imaging systems record
imagery simultaneously with Global
Positioning Systems (GPS) and Inertial Measurement
Units (IMU).
The resulting data are combined
with Ground Control Points (GCPs) or Replacement Sensor
Models (RSMs), and Digital Elevation
Models (DEMs) to
produce accurate photo-basemaps.
Standardized methods to measure
geospatial registration accuracy are explained in
these
definitions.
- CE90, (Circular Error of
90%). CE90 is commonly used for
quoting and validating geodetic image
registration accuracy. A CE90 value is the
minimum diameter of the horizontal circle that
can be centered on all photo-identifiable GCPs
and also contain 90% of their respective twin
counterparts acquired in an independent geodetic
validation survey.
- LE90,
(Linear Error of 90%). LE90 is
commonly used for quoting and validating DEMs
and topographic contours. A LE90 value
represents the linear vertical distance that 90%
of control points and their respective twin
matching counterparts acquired in an independent
geodetic validation survey should be found from
each other.
- RMSE, (Root Mean Squared
Error). RMSE is commonly used for
quoting and validating geodetic image
registration accuracy. A RMSE value is a single
summary statistic that describes the square-root
of the mean horizontal distance between all
photo-identifiable GCPs and their respective
twin counterparts acquired in an independent
geodetic survey.
- 1-Sigma, (Standard
Deviation Error). 1-Sigma is used for
quoting and validating geodetic image
registration accuracy. 1-Sigma is the
minimum diameter of the horizontal circle that,
when centered on all of the photo-identifiable
GCPs, would contain one Standard Deviation
(i.e.: ~68%) of the population of all available
twin counterparts acquired in an independent
geodetic survey. This is provided that the
GCP population is sufficiently large for their
relationship to be "normally"
distributed.
Approximate
mapscale
equivalencies, based on U.S. National
Map Accuracy Standards ...
| Map Scale |
CE90 |
LE90 |
RMSE |
1-Sigma |
| 1:2,400 |
2 m |
0.2 m |
1 m |
1 m |
| 1:4,800 |
4 m |
0.4 m |
2 m |
2 m |
| 1:12,000 |
10 m |
0.8 m |
5 m |
2 m |
| 1:24,000 |
12 m |
1.3 - 5 m |
6 m |
3 m |
| 1:50,000 |
25 m |
2.5 - 10 m |
15 m |
12
m | |
