International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004
overlapping images that are captured at six different locations
with 90° rotation around the Z-axis at each exposure station, and
are roughly four to five meters away from the closest point on
the test field. The position and orientation of each captured
image are shown in Figure 4.
SONY DSC-F707 digital camera is implemented for calibration
and stability analysis. The price of this camera is roughly $700
USD. It is a Single-Lens Reflex (SLR) camera with a Charged-
coupled Device (CCD) has a resolution of 2560 x 1920 pixels
and 0.004 mm pixel size.
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Figure 4. Position and orientation of eighteen images used for
calibration
An automatic procedure for measuring the end and intermediate
point coordinates along the lines in the involved imagery has
been implemented (Habib and Morgan, 2003). For each line in
the image space, eighty intermediate points were automatically
extracted with sub-pixel accuracy.
Experiments were carried out using line-based self calibration
to determine Interior Orientation Parameters of the camera and
investigate the stability of these parameters. Derived estimates
of camera interior orientation parameters at different times are
shown in Table 1.
July 03 | October 03 se
o, 0.002595 0.0019374 0.002231
E sn) -0.114675 -0.0898 -0.090895
fot 20.001023 | 20.000858 | + 0.000902
-0.076494 -0.068292 -0.065772
po (rm) 40.001063 | 20.000871 | 24 0.000906
tan 11.620700 11.6371 11.6233.
+0.002158 | 20.001897 | 0.002017
E -0.001176 -0.001225 -0.001227
+1.4730e-6 | + 1.3882e-6 | +1.3614e-6
Table 1. Estimates of the interior orientation parameters
For stability analysis, reconstructed bundles from the three
different IOP sets in Table 1 were compared to check the degree
of similarity between the reconstructed bundles (Habib et al.,
2004). The results proved the stability of the internal
characteristics of the camera. Therefore, it can be used for an
accurate estimation of three dimensional coordinates as shown
in the next section.
4.2 3D-Reconstruction
Architects need different types of data for the derivation of
detailed plans in order to precisely reconstruct historical
buildings. Generally, views, cross-sections, ground plans or
complete 3D CAD models are required. Photogrammetric
techniques are used to provide these products.
After estimating the interior orientation parameters of the
camera, experiments are conducted based on real data to build a
three dimensional model for a historical church in downtown
Calgary, Canada, Figure 5. For this purpose, the calibrated
SONY DSC-F707 digital camera is used to capture thirty-nine
convergent images at three different locations with 90? rotation
around the Z-axis at each exposure station. An arbitrary datum
is chosen as reference for the object space, where 115 points are
selected in the front side of the church. These measurements are
introduced into the bundle adjustment in order to estimate their
ground coordinates. Selection of the points was performed
while considering the following issues:
* Distribution of points. The measured points have to be well
distributed and cover the whole object under study.
= Visibility of each point in two or more images. If the same
points appear in larger number of images, the geometrical
strength as well as the accuracy of three-dimensional
coordinates will be improved.
= Adequacy of selected points for the reconstruction of
different shapes from an architectural point of view. For
example, to draw a circle, at least three points on the
circumference have to be located.
Figure 5. Historical church in downtown Calgary, Canada
As shown in Figure 6, the three dimensional coordinates
resulting from the adjustment procedure are introduced into a
CAD model.
Figure 6. AutoCAD wire frame representation of the historical
church
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