mportant 
ways of 
to each 
s part of 
ereo pair 
as a staff 
je a scale 
'hest cost 
al surface 
netrically 
the adja- 
proposed 
staffs in 
raphed in 
A. scale 
tographed 
d a scale 
tographed 
Figure 3 
a pair of 
e left side 
ind Image 
: left side. 
me as the 
geometric 
of images. 
) between 
e adjacent 
way. 
  
ight 
ct 
  
  
  
  
  
  
  
  
  
  
Index Index 
Image L i Scale Image R 
: oy | etailed 
bomen mage i 
Object 
Camera # 
Camera L Camera R 
  
  
  
  
  
  
(a) Image acquisition 
  
  
  
  
  
  
  
  
  
  
  
   
  
  
  
| FE 
ImageL | || | Image R 
| 
| Detailed E 
Image i | 
= Object 
Coverage of Coverage of 
Index Image R Index Image L 
(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 
image. 
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 
load. 
  
  
  
  
  
  
  
  
  
  
  
HO AO Diobuaxen mandata 
  
Figure 5. Measurement of image coordinates of control points 
—189—