3.1 OrthobasePro v8.6
In use of the OrthobasePro, there are some stages that should be
followed. In the following, the steps will be described.
3.1.1 Model definition
The first step is to define the kind of model for OrthobasePro,
which is shown in Figure 10.
PP A E S xj
Select Geometric Model
Digital Camera ES i
Video Camera [Videography) | Cancel |
Non-Metric Camera | =
DPPDE | |
æ|
Generic Pushbroom
SPOT Pushbroom
IRS-1C Pushbroom
IKONOS
Figure 10. Model definition in Orthobase Pro v8.6
The SPOT Pushbroom model is selected. In OrthobasePro v8.6,
this model is designed for SPOT1-4, but it has the capability to
be modified for SPOT 5. The SPOT model in ERDAS uses the
bundle adjustment and it uses polynomial order for orbit
modeling.
3.1.2 Data Input
The images imported into the software with Import/Export
module. The user can use TIFF format for import because in
ERDAS Imagine v8.6, there is no option to read the data and
the header of the data directly as SPOT 5 image. After
importing, the images are added to the OrthobasePro.
3.1.3 Interior Orientation (Frame Editor)
In this stage, the interior orientation parameters for SPOT 5 will
be modified, e.g. the user will give the focal length, number of
pixels in each line and the incidence angle. As the
OrthobasePro uses polynomial for orbit modeling, user should
specify the polynomial order for the orbital parameters such as
X, Y, Z, Omega, Phi, Kappa.
3.1.4 Point Measurement
The next step is to select Ground Control Points, Check Points
and Tie Points. For Rasht region, with using the provided
digital maps, the 17 GCPs and CPs (Full Control Point) are
selected. These points are in accuracy of 1:25000 maps. The
selected points are the same as the points selected for PCI
software. Figure 2, Figure 3, and Figure 4 show the distribution
of the GCPs and CPs. The digital maps do not cover the whole
imagery area and they cover about 6096-7596 of the whole
images. In GCPs selection, it was tried to distribute them in the
entire image. As a result, this kind of coverage makes the error
to be distributed in the entire image homogenously and doesn't
let extrapolation happen in the image.
The ERDAS Imagine also has the ability to extract the tie
points automatically. Because it is tried the conditions to be
similar for both software, again 13 automatic tie points selected.
But the tie points are not the same as they are dependent to the
software algorithm to find and extract them.
3.1.5 Triangulation
After doing point measurement process, the bundle adjustment
(triangulation calculation) will be done. The test has been done
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004
Internc
with changing the GCPs to CPs and vice versa and also
removing Tie points or contributing them in the calculations.
The result of these tests is:
1- The role of tie points in the calculations is important.
2- The minimum number of GCPs for solving model is Figure
dependent to the polynomial order selected by the black
user for the orbit parameters. The polynomial order
for each parameter that is selected for this study is: X
order 2, Y order 2, Z order 2, Omega order 0, Phi
order 0 and Kappa order 2. Based on that, the
minimum number of GCPs selected is 6 points for
each image (or 6 common GCPs).
There
RMS E
Avera
proces
The result of the bundle adjustment for 6 GCPs for each image
and 13 tie points is shown in Table 3.
GCP CP
iround X (m) 0.001 16.118
Ground Y (m) 0.016 20.219
Ground Z (m) 0.000 38.564
Image x (pixel) 3.246 3.563
Image y (pixel) 1.922 1.764
Table 3. The RMSE of the Orthobase v8.6 bundle adjustment
There are 6 GCPs per image, 5 common CPs, and 13 tie points
Please see the Appendix I for more information about the used
points.
3.1.6 Automatic DTM Extraction
After solving orbit modeling parameters, the software can start
processing for automatic DTM extraction. This software uses
Correlation function for image matching.
3.1.7 The DTM result
Table 4 shows the error analysis on GCPs and CPs in the DTM.
Calculated GCP/CP
ID Elevation (m) Elevation (m) Difference (m)
] -28.225 -25.814 -2.411
2 No matching
3 No matching
4 No matching
5 -100.011 5.418 -105.43
6 No matching
7 418.863 499.656 -80.793
8 203.786 218.974 -15.188
9 115.024 11.032 103.09
10 -31.894 -22.514 -9.38
11 118.47 -22.267 140.74
12 9.925 1.576 8.349
]3 111.034 49.411 61.623
14 -69.504 -22.076 -47.428
15 -28.559 -21.47 -7.089
16 231.363 474.2 -242.84
17 29.424 -11.028 40.452
Table 4. The error analysis on GCPs and CPs in the generated
DTM by OrthobasePro v8.6
