es were captured
construction made of
the boards were not
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were long. To enable
ld was photographed
fabout 1:8to 1: 10
of about 30 to 40 cm.
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ym the camera to the
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every stereo pair can
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ould be used in any
as photo equipment
camera over a small
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r another line that is
"sition of one leg and
the required distance.
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' when generating the
on the illumination,
. For a good stereo
o images should be as
ishes connected to the
ase the position of the
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ation or sunlight can
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ved any more. Even if
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he whole scene. This
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high quality lenses is
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re rather dark. One of
, for the other location
images were taken in a
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or the photogrammetric
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the images for stereo-
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06.
it Making Referencing Project Display Window Help
= Ee BEB BQ RAO
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| Source Data
i Photograph # 8
| Number of dangles: n/a
| Mapping plane points. [95,9293 Reorder |
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| ir Image Scale | pinels per I 4 |
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low resolution preview 50x38
7 = _ = .
Figure 2. Generation of a rectified image using PhotoModeler®
DATA PROCESSING DURING THE FIELD CAMPAIGN
Image Rectification. The rectification of the vertical images is
probably not necessary in many cases. If no height information
of the object is available (just like in this case) and the object is
not really flat, i.e. has some extent in the 3" dimension, the
result of this process can only be a simply rectified image, i.e.
not an orthophoto. Nevertheless, there are reasons to do this
type of processing. Generating rectified images using the
marked points leads to images that are orientated in a unique
reference system and which have an approximately identical
scale when printed. The rectification can be done using software
like PhotoModeler®, which is an easy to use digital
photogrammetry software. Otherwise, standard image
processing or graphics software can be used to perform a coarse
rectification and a resampling to a certain resolution. In this
case the influence of the central projection will not be corrected,
but dependent on the lens used (if not a fisheye) this can be
accepted in many cases. It is important to realize and make
understood to all persons involved, that these images are not
metric image maps, but only image representations of the
situation suitable for obtaining a general view or for numbering
etc.
In this project, the images were rectified using
PhotoModeler® software (cf. fig. 2) and resampled for printing
in a scale of 1:10 on A4 sized paper. The processing of the
images was performed in the evenings, so that results on paper
and the laptop screen could be presented to the partners the next
day. The images are rectified in the plane of the marked control
points, displacements remain where height differences occur.
Anaglyph images. An anaglyph image is an image that
contains the image information of two single images taken from
different positions. If the geometric conditions (parallel axes of
exposure, reasonable base to height ratio) are complied with and
each eye is provided with the image information of one image,
the observer can see the situation in stereo. When the geometric
conditions are fulfilled during the image capture, the separation
of the image information can be done using different
techniques. A simple method is the separation of the images
using different colors for the two images. These colors must be
independent from each other. Two color combinations are quite
popular for this procedure: red-green and red-cyan images. The
red-cyan combination is better for color images, red-green
rather for black and white images. With both methods, the color
information of the images is strongly reduced. If the color
information of the objects is essential even in 3D, these methods
are not suitable, others should be taken into account like
separation using polarization or shutter glasses. The latter have
the disadvantage, that they cannot be used as easily. If the color
information is not essential, or black and white images are used,
the generation of the images is quite easy. In principle, the
intensities of the single images are mapped to the intensity of
the appropriate channels in the stereo image. The positions of
the different color layers must be adjusted to let the parallaxes
disappear for a chosen plane (here defined by the marked
points). For objects in front of or behind this plane, the
horizontal parallaxes represent height differences of the object.
Thus, this simple technique leads to reasonable results only if
the height differences from this plane are not too large. After the
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