International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
Fix) = Xo + (Hp/2 - 2) Sp -
pee (x) m12 F1(y)'+m13F1 (7) | 4
m31F1(x)'+ m32 F1(y)'+m33F1(2)’ (®
Fiy)= Yo + (Vp/2 - 2) Sp -
m 1F1(x)'+ m22 F1(y)'+m23F1(z) | 5)
m31F1(x)'+ M32 F1 (y)'+M33F1 (7)' (
Where Fx, and Fy,= principal points of the image
Hp - number of horizontal pixel
Vp = number of vertical pixel
Sp = pixel size
f = camera focal length
m's = function of the rotation angles omega, phi, kappa
Fl(x), Fl(y)', F1 (z)' = rotate image coordinates are
related to the measured photo coordinates Fl(x) and
F1(y).
Coordinate of F?, F3 and F, can be derived by using Equations 1 -
5. The general formula can be defined in Equation 6 and 7.
Fn a) = Fx, + (Hp/2- 2) Sp +e
Fny)= Fy, + (Vp/2- 2) Sp + €
(6)
(7)
Where Fax and Fy, = position of diagonal coordinate x and y
In this study, all measured coordinates were used in the image
processing for the production of digital orthophoto and digital
elevation model. As mentioned in the data acquisition section, all
acquired images will be processed by using photogrammetric
software. In this study, for each photograph three control points
were established; One control point was obtained from the
principal point and the other two control points were measured
from the proposed equations (Equation 6 and 7). These three
control points were used to rectify each photograph and all
rectified images were mosaiced to generate digital orthophoto of
the study area. The result of digital orthophoto and digital
elevation model is discussed in the result section.
3.2 Image processing based on Google Earth control points
The second method for image processing in this study used
Google Earth coordinates as control points. Several control points
were captured in Google Earth and were used for exterior
orientation in the production of digital orthophoto and digital
elevation model. The photogrammetric product can be computed
Digital Orthophoto d xis
496
after going through certain photogrammetric steps such as interior
orientation, exterior orientation, aerial triangulation and bundle
adjustment. The results of image processing by using Google
Earth coordinates and GPS onboard were compared and analyzed
in the discussion section.
3.3 Data Verification
Photogrammetric products must be verified before they can be
used for any applications. There were 57 checkpoints that were
randomly distributed evenly for the whole study area. Each
checkpoint was established by using Real Time Kinematic (RTK)
GPS which required only 2-3 minutes per control point. The
accuracy assessment of photogrammetric product in this study is
discussed in the analysis section.
4. RESULTS
The result can be discussed in two cases; first case is the
results of image processing by using proposed image registration
algorithm and second case is the result of image processing by
using control points from Google Earth coordinates. There were
two photogrammetric products produced in this study, namely
digital orthophoto and digital elevation model. The size of image
block for this area is about two kilometer by two and half
kilometer where 228 images were captured during flight mission.
Spatial coverage of one image is about 326 meter x 245 meter.
Each overlapped images were about 60 percent and sidelap were
about 30 percent. These results were described in Figure 4(a) and
Figure 4(b). Figure 4(a) shows the product of digital orthophoto
after the rectification processes by using the proposed image
registration method. The advantage of the proposed method is that
the images can be rectified by using diagonal coordinate which
was defined from the proposed algorithm and improve image
matching during auto-tie point measurements. Rectified images
were mosaiced and digital orthophoto was created for the study
area. Figure 4(b) shows the product of digital orthophoto based on
control points acquired from Google Earth coordinates.
Based on Figure 4, in graphical view, there is no difference
between the digital orthophoto for both techniques while for the
digital elevation model there were slight differences. This might
be caused by inconsistency of Google Earth and onboard GPS
coordinates used as control points in image processing. It is
because coordinates obtained from Google Earth and onboard
GPS has some error that need to be considered. However, the
details on the accuracy of the assessment of both results are
discussed in the dicussion section.
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Digital Elevation Model
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