The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008
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of 3 comparing digital image matching in DMC images to
manual point identification in analogue images.
Analog semiaut.
DMC semiaut.
DMC MatchAT
pm
pix.
pm
pix.
pm
pix.
x 4.83
0.32
2.85
0.24
1.23
0.10
y 4.27
0.29
2.35
0.20
1.12
0.09
Table 1: Photogrammetric residuals in pm and pixel (Alamus et
al., 2005)
Image pointing accuracy using AAT techniques with analogue
images is in the level of 4 to 5pm (i.e. l/3 rd of a pixel when
scanned at 15pm), with DMC images it is in the level of 1.1 to
1.4pm (i.e. 1/10 th of a pixel).
2.2 Small scale flights
To test the performance of aerial triangulation check points
from several blocks have been analyzed. The analysis has been
carried out in two different data sets: blocks with a GSD of
45cm, studied in this section and blocks with a GSD of 7.5cm,
studied in the next section.
ratio” (when taking b as the base between images from different
strips) plays an important role (and that value is similar in the
analog and digital scenarios).
Figure. 1 : Aerotriangulation check point accuracy vs. year of
flight
From year 2004 to 2007 ICC, in collaboration with the PNOA
project, is flying and aerotriangulating half Catalonia at a GSD
of 45cm, which corresponds to approximately 5000 DMC
images every year. The check points used in the comparison
were obtained from the 50 blocks used to aerotriangulate the
20 000 above mentioned images. It is important to point out that
the used blocks are taken as they are without any kind of
additional optimization. Therefore, the accuracies shown in the
paper corresponds to a day to day work in a production
environment rather than the result of an academic effort.
The accuracies of the check points shown in table 2
demonstrate that there is a slight improvement in the three
coordinates when the DMC camera is used.
RMS X
(m)
RMS Y
(m)
RMS H
(m)
N.Checks
Analog cameras
0.22
0.20
0.28
90
Digital (DMC)
0.21
0.19
0.26
280
Table 2: Comparison of the analog vs. digital check point
accuracies for 45cm GSD
In 2004 the ICC already had many years of experience in aerial
triangulation of analog projects, but with the reception of the
first DMC, in late 2004, some parts of the workflow had to be
readjusted and some “know-how” had to be acquired (use of
self calibration parameters, quality of GPS/IMU information,
error propagation...) During the first 3 years of DMC operation
an improvement on the quality of the aerial triangulations has
been observed, which is attributed to the learning curve of the
new technology. Figure 1 shows the check point accuracy by
year and a slight yearly improvement can easily be observed.
The matching accuracy improvement observed in the
correlation of digital images has not been translated to a big
improvement in the horizontal accuracy because the check
points are measured manually without any automatic or
semiautomatic support. Concerning the small improvement in
the vertical component, despite of the worse b/h factor, it has to
be noticed that most of the check points are measured in images
from different strips (flown at 25% side lap) so the “side lap b/h
2.3 Large scale flights
Regarding the results from large scale flights, the check point
accuracies from 25 different blocks are shown in table 3. The
data corresponds to production urban projects with a GSD of
7.5cm for both digital and analog (scanned at 15pm) flights.
RMS X
(m)
RMS Y
(m)
RMS H
(m)
N.Checks
Analog cameras
0.032
0.050
0.059
19
Digital (DMC)
0.035
0.041
0.058
117
Table 3: Comparison of the analog vs. digital check point
accuracies for 7.5cm GSD
For the combined horizontal accuracy, a very slight
improvement in the digital flights can be observed while the
vertical component of the accuracy remains stable. It has to be
pointed out that the relative accuracy of the check points is at
the level of 2cm, therefore it is possible that a portion of the
residuals from the check points is due to the uncertainty of the
ground coordinates.
As in the previous section the accuracy of the three components
is very similar in analog and digital blocks. The explanation
might be the same as in the previous section. The image
observations of the check points are given by manual
measurements (not taking advantage of the superior image
correlation of the digital image) and in different strips (taking
advantage of the side lap b/h ratio).
3. DEM GENERATION
This section describes and discusses the obtained accuracies of
automatically DEMs derived for the same area from three
different flight configurations The DEM are created using the
commercial software package Match-T of the Inpho Company.
The 3 flights were taken in a 3 year time difference with an
analog RC30 camera at a ground pixel size of 45cm and with
the DMC at a GSD of 45cm and 20cm. The major
characteristics of the 3 corresponding blocks are listed in table 4.