PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
April 2017
259
CASE II — T
esting
M
ethodology
, N
umber
and
C
onfiguration
of
G
round
C
ontrol
N
etwork
Seven scenarios, A through G, were examined during the
evaluation (see Figure 10). Scenario A, where no control
points used in the processing, is not shown in Figure 10.
CASE II — H
orizontal
A
ccuracy
E
valuation
The horizontal accuracy of the orthorectified imagery was
assessed in a similar fashion to the method used in Case I.
Table 2 lists the summary of the horizontal accuracy statistics
for each of the seven scenarios.
CASE II — V
ertical
A
ccuracy
E
valuation
The vertical accuracy of the point clouds was assessed in a
similar fashion to the method used in Case I. Table 2 lists
a summary of the vertical accuracy statistics for each of the
seven scenarios.
Figure 10: Ground Control Evaluation Scenarios for Case II. (Blue triangles represent control points used in the processing.)
R
esults
A
nalysis
UAS R
esults
—
From Table 1, Case B, it is obvious that for
a small square or rectangular shaped project similar to the one
discussed in Case I, one can obtain submeter horizontal and
vertical accuracy from UAS-derived products without having
any ground control points used in the processing, i.e. airborne
GPS only. However, with four ground control points, one at
each corner of the block, the horizontal accuracy is stabilized
to under 0.20 feet. Additional ground control points, beyond
the four corner points, do not seem to benefit the horizontal
accuracy of the block (see Case C of the table). The story is
little different for the vertical accuracy, as the four corner
points did not result with the desired vertical accuracy.
Reasonable vertical root mean squares error (RMSEv) was
only reached after adding a fifth ground control point near
the center of the block. Adding more ground control beyond
the five points did not improve the vertical or the horizontal
accuracy of the block, see Table 1 and Figure 7.
R
enaissance
R
esults
—
From Table 2, Case A, it is obvious
that for corridor-type projects similar to the one discussed in
Case II, that we can obtain 5-foot
horizontal accuracy and 14-foot
vertical accuracy for products derived
from UAS-surrogate system flown
from a manned aircraft at an altitude
of 1,100 feet AGL without having
any ground control points used in the
processing, i.e. airborne GPS only.
The coarse vertical accuracy in Case A
can be attributed to the combination
of the uncalibrated focal length of the
lens on the camera and the rough
Table 2: Horizontal and vertical accuracy of Renaissance products, Case II.
Accuracy Term
Processing Scenario
A
B
C
D
E
F
G
Number of Control Points
0
4
6
8
10
21
38
Number of Check Points
38
34
32
30
28
17
0
RMSE E (ft.)
4.47
0.23
0.16
0.18
0.13
0.05
0.05
RMSE N (ft.)
1.89
0.26
0.20
0.14
0.14
0.07
0.05
Radial RMSE N,E (ft.)
4.86
0.35
0.26
0.23
0.19
0.08
0.06
RMSE Elev. (ft.)
13.51
0.54
0.71
0.40
0.35
0.26
0.17
Horizontal Accuracy at 95% (ft.)
8.40
0.60
0.45
0.39
0.34
0.14
0.11
Vertical Accuracy at 95% (ft.)
26.49
1.05
1.40
0.78
0.69
0.52
0.34
