(1) Input by scanner
Aerial photograph is inputted by drum scanner
as the image data to be proc-essed. It may be
possible in the future to directly input the
data through CCD camera, but it is practical at
present to input it from a photograph. Input
method is RGB full color input from a film or
paper. Input resolution is in the range of 1
pixel = 0.005mm - 0. 250mm.
(2) Orientation & Rectification
Since each kind of orientation method has been
established in the field of aerial photogram-
metry based on the precise geometric model as a
preliminary processing, we used the orientation
results of existing analytical stereo plotter
(such as PLANICOMP) in this system. After the
completion of orientation, we made rectifi-
cation to eliminate vertical parallax. As a re-
sult of these processes, stereo view is obtain-
ed on the monitor, stereo matching is made ef-
ficiently, and matching accuracy is enhanced.
(3) Compilation of image pyramid
As a preliminary processing to enhance the pro:
cessing efficiency of stereo matching, the
image pyramid is made by sequentially reducing
the rectified images to the size of 1/2. The
image pyramid is made by the simple method to
usethe average value of 2 x 2 pixels as one
pixel of one rank higher hierarchy.
(4) Stereo matching
The stereo matching is started from the most
coarse hierarchy of image pyramid, and matching
points are converged by sequentially conveying
the information to finer hierarchies. At each
hierarchy, the square grid is placed on the
left image, and matching point is found out on
the right image by one dimensional search of
image correlation method.
(5) Edition and correction
Many mis-matching and unmatching occur in ster-
eo matching based only on the image correlation
method. As a solution for practical use, there-
fore, we made it possible to have stereo view
on the monitor by using the liquid crystal shut
ter glasses. Namely, edition and correction are
made to the stereo matching result while visual
ly confirming on the monitor. The data manipul-
ation on the monitor is done by the software of
image display/edition group.
(6) DTM and digital orthoimage
After the matching points are determined on
left and right images, three dimensional infor-
mation of each point is obtained from orient-
ation factors and geometric principles. Next,
the information is interpolated and made as DTM
by re-organizing the meshes so that they form
square grids against the ground coordinates.
Interpolation is made by the software of 3-D
mesh compilation group. Lastly, the digital
orthoimage is compiled using rectified images
and DTM.
4. Compilation of verification data
We used this system and compiled DTM and digit-
al orthoimage from a pair of aerial stereo pho-
tographs. The scope of processing and the data
used are as follows:
x Scope of processing: East part of Fukuyama
City, Hiroshima Prefecture (2.2km x l.4km)
x Data used: A pair of aerial color stereo
photographs at the scale of 1:12500 (1987)
* Materials used: Topographic map, 1:2500 &
1:10000 (published in 1987)
(1) Data input and preliminary processings
We used positive photographic film for aerial
color photograph, and inputted it at the reso-
lution of | pixel = (.050mm. Rectification was
made by re-arranging the image data so that
matching points of left and right images may
align on one straight line basing on the orient-
ation results of analytical stereo plotter. The
data of 5 hierarchies were made as the image
pyramid. One pixel of the coarsest hierarchy
corresponds with 16 pixel x 16 pixel of the
finest hierarchy.
(2) Stereo matching and edition/correction of
matching results
We made stereo matching based on image corre-
lation method using the image pyramid. The mat-
ching results were stereo-displayed on the mon-
itor each time when the processing of one hier-
archy was completed, and correction was made to
the mis-matching. The matching points were plac-
ed so that their interval should be 5m on
ground at final step. Fig.4 shows a part of mat-
ching result at the third step.
(3) Compilation of DTM and digital orthoimage
After obtaining three dimensional coordinates
from the matching results of the last step, we
made DTM by re-sampling them as to form square
grids at the interval of 5m on the ground. We
also compiled the digital orthoimage from the
rectified images and DTM. Fig. 5 is the DTM ex-
pressed by contour lines, and Fig. 6 is the dig-
ital orthoimage of the same area. In addition,
we made DTM using theanalytical stereo plotter
by the same specification for verify the ac-
curacy, etc. However, the measurements obtained
290
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
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