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Close-range imaging, long-range vision

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(a) Image acquisition

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Coverage of Coverage of
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(b) Image coverage
Figure 4. Two-stages image acquisition
(3) Two-stages image acquisition
Since spatial resolution of lower price digital cameras for
nonprofessional use is worse than one of analog cameras, it
takes a long time and a high cost to take stereo images all
over the object with spatial resolution requested for some
purposes such as preservation or restoration of cultural
heritages. Therefore we devised a two-stages image
acquisition way for saving time and cost. Figure 4
illustrates two-stages image acquisition. At the first stage, a
pair of stereo images covering the whole object is acquired
by parallel photography or convergent photography. We
call this pair of images index images. Index images are
used for extraction of a DSM used at generation of ortho
images, and for orientation of detailed images that are
acquired at the second stage. Spatial resolution of index
images is worse than requested resolution of an ortho-image,
but is sufficient for both DSM extraction and orientation of
detailed images. At the second stage, detailed images are
taken with requested spatial resolution. It is not necessary
to take a stereo pair image or to cover all over the object. A
detailed image is taken of an interesting part of the object,
and it is referenced to a mosaicked ortho image of index
images. A scale such as a staff in leveling is taken in a pair
of index images to give a scale of a geometrically corrected
3.3 Measurement of Image Coordinates of Control Points
and Pass Points
Positions of control points and pass points on images are
measured on a PC display. Marked points on a scale are treated
as control points in our method, and object space coordinates of
control points are not required by our method. Two horizontal
or vertical adjacent images are displayed on the computer
screen, and an operator clicks at a control point or a pass point
on the screen. Clicked position of a point on the image is
measured and image coordinates of the point are recorded.
Measurement of image coordinates of control points and pass
points is one of the major manual operation of the method.
In case of the two-stages image acquisition, a mosaicked ortho-
image of index images is utilized as a base map at orientation of
each detailed image. On the one hand a stereo pair of index
images is shown on a PC display at processing of index images,
on the other hand a mosaicked index image and a detailed
image is shown on a PC display at processing of detailed
images. Figure 5 shows a screen for measuring image
coordinates of control points at processing of detailed images.
Left image in the screen is a mosaicked index image and right
one is one of detailed images. Resolutions of these two images
can be found different.
Template matching assists an operator to search the correspond-
ing position of a control point or pass point to lighten operator's

HO AO Diobuaxen mandata

Figure 5. Measurement of image coordinates of control points