Geospatially referenced
ortho-rectified imagery offer photographic information referenced to accurate geodetic
models to support planimetric compilation of scaled mapping themes. The ortho-rectification
process eliminates various error factors.
During deployment
of an earth-imaging system, imagery are recorded simultaneously with data from Global Positioning
Systems (GPS)
and Internal Measurement Units (IMU).
In order to produce highly accurate ortho-rectified planimetric-mapping imagery
sources, imagery must be adjusted by Digital
Elevation Models (DEMs),
and surveyed
Ground Control Points (GCPs),
or Replacement Sensor Models (RSMs).
The actual
geospatial
registration accuracy (i.e.:
production processing expense) required for any given
project, really depends on our
customers' specific end-use application. Some applications do not require
ortho-rectification. This is why our all of our geospatially referenced products are always
initially quoted and ultimately delivered
with one of the following industry standard measurement values
...
-
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 |
|
