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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BS. Istanbul 2004
exposure stations and reference lines related to all planes of an
object. 3D orthogonal coordinates were formed as the direction
parallel to that of a reference line was X-axis, photography
direction was Z-axis and the direction perpendicular to Z-axis
is Y-axis, for analyzing 3D coordinates of an object.
For applying digital photogrammetry, this study used Photo
Scanner(Minimum Pixel Size: 7.5 ) that enabled self-
compensation on image distortion caused by scanning. Film
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Figure 2 Scheme of exposure plan.
images were converted to digital images of high resolution
While pixel sizes are very important in determining resolution,
if pixel is reduced, a relevant file size becomes increased so
that small pixel sizes influence on image processing rates. Thus,
with respect to file sizes of images, processing rates of images
Figure 3 Aerial Photography of Site
and analysis accuracy, pixel sizes were defined as 15pm for
facilitating effective image analysis on a computer. In addition,
Figure 4 Stereo digital Images
aerial photography on relevant area was used to make a site
map around an object and roof plan. The scale of aerial
photography taken at an altitude of about 800m was 1:5,000.
Two dimensional pictures were used for preparing digital site
plans. For this purpose, aerial photography was scanned with
the resolution of 15pm using Photo Scanner and then was
converted to digital images to generate drawing. Figure 3
shows aerial photo on the main building of Korea University,
an object, and surrounding areas.
3. MEASUREMENT OF REFERENCE POINT
For acquiring 3D digital data for all planes of a structure, it is
required to unify coordinate system which is called the same
coordinate system. For measuring reference points on the same
coordinate system, coordinates of reference points on four
planes of a structure were measured using Monmos(Sokkia) 3D
Station and connection points linking each plane were also
arranged and measured. Moreover, for examining reliability of
measured values check points were evenly distributed
for
verifying accuracy. Target sizes were set to be taken with
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Figure 5 Distribution of Reference Points (Front Side)
minimum 307] on captured images. For measuring reference
points, reflective targets were installed on the center of target.
Reflective targets were 0.47 thick and RS10, RS20 and RS30
were prepared according to distances. They were evenly
distributed on a relevant plane. Figure 5 describes the
distribution of reference points arranged on the front side of an
object. At least 6 reference points were distributed on each
dimensional model. And the number of reference points was
adjusted and arranged in consideration of analysis area of a
model and photography conditions around an object. The
origin and the reference line defining a coordinates system
were set in parallel with an object plane with the front
line of 5.1094m, 10m from the front side (front.1) of a
building. Then, 3D coordinates system established with X-axis
as the reference lie and Z-axis as the photography direction. In
this case, multiple connection points and check points were
arranged with respect to the size of an object so that all
reference points were located on the same coordinates system.
Deviations in X-axis, Y-axis and Z-axis caused by movement of
Mono Mobile 3-D Station were adjusted to be within 0.5mm
each. According to rearrangement of all planes of an object,
rearrangement error was 1/13,000 that could be considered as a
proper result. It was also confirmed that all reference points
were measured in conformity with required precision.
4. ACQUISITION OF DIGITAL 3D MODEL
For acquisition of 3D digital data using digital images,
VirtuoZo Software was used as a digital data acquisition system.
VirtuoZo entered coordinates of reference points acquired by
Mono Mobile 3-D Station after creating new blocks and
entering detailed information on a camera. Next, digital data
was converted to files in a format that could be recognized by
VirtuoZo. After interior and exterior orientation for left and
right images, dimensional models were generated and drawn.
