International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004 
effect covers the whole block seamlessly. Two such seamless 
mosaics could be produced. One is produced from all the left 
images, leading to a left mosaic, and the other produced from all 
the right images, leading to the right mosaic. 
To produce a stereo view, parallax needs to be introduced to one 
of the mosaic (e.g. the right mosaic) to form a so-called mosaic 
stereomate. The value of the parallax for each pixel is a function 
of the height at its position. Then the left mosaic and the mosaic 
stereomate form a seamless stereo model. 
Such a seamless stereo model is good enough for visualization 
purpose. However, for accurate measurement, it is not good 
enough, as discussed in Section 2. Therefore, such a seamless 
stereo model is still not measurable in a sense. 
To make the accuracy as high measurement, the following 
strategy is adopted here in this study: 
Q The 6 orientation parameters of each image are recorded 
in a file (i.e. orientation file); 
Q The linage of each pixel on both the mosaic orthoimage 
and mosaic stareomate is recorded. That is, for each point 
(pixel) on the seamless stereo model, the system knows (a) 
the (original) left and right images where it is derived; (b) 
the orientation parameters of both images; and (c) its 
image coordinates on both images. 
@ With such information, when measurement is performed, 
the ground coordinates of each point on the seamless 
stereo model is directly computed from original 
stereo-pair instead of the image coordinates on the mosaic 
orthoimages and mosaic stereomate. 
Such a seamless stereo model is called the measurable seamless 
stereo model. 
4. PRACTICAL ASPECTS OF A MEASURABLE 
SEAMLESS STEREO MODEL 
4.1. The generation procedure of measurable seamless 
stereo model 
The flow diagram for generating a measurable seamless stereo 
model is given in Figure 2. The procedure can be divided into 
three major processes: 
Q First, to produce the left and right mosaic orthoimages: 
When such two images are viewed stereoscopically, the 
terrain is seen to be flat; 
@ Second, to introduce parallax to form a mosaic stereomate: 
the horizontal parallaxes are computed according to a 
DTM. Figure 2 illustrates the procedure; 
® Third, to index the lineage of each pixel on both the 
mosaic orthoimage and mosaic stereomate. 
More detailed explanation of the steps expressed in Figure 2 is 
given as follows: 
(i). Generating digital orthoimage: Orthorectfication for every 
aerial image in the block is performed to produce the 
orthoimage using the interior and exterior orientation 
elements and DTM. This can be done at a digital 
photogrammetric workstation. The extent of the orthoimge is 
decided according to the valid extent of the aerial image. 
(ii). Constructing photo-pair stereo models: stereo photo-pair 
models are built in block area according to the adjacent 
relationship between aerial images along flying line. Every 
photo-pair stereo model contains a left and a right original 
aerial image. 
(iii). Choosing the seam lines among adjacent models: The seam 
lines can be automatically chosen or by manual. As the 
image surface objects are displaced along the radiation from 
the nadir, in order to make seamless mosaic, the seam lines 
should keep away from such objects. But the seam lines 
cannot exceed the overlapping area among adjacent stereo 
photo-pair models. 
(iv). Constructing the valid mosaic polygon for every stereo 
photo pair model: The valid mosaic polygons are 
automatically constructed according to the relationships 
between the seam lines and the seam lines or between the 
seam lines and edge lines. 
(v). Generating left and right mosaic orthoimages: The left and 
right mosaic orthoimages are made separately according to 
the valid mosaic polygon of every photo-pair model in the 
photographic block area. 
(vi). Introducing the horizontal parallaxes for one of the two 
orthoimages: X-parallaxes are introduced to one of the 
mosaic orthoimages according to the DTM of the area. 
  
The original aerial images, corresponding interior and 
exterior orientation elements and DTM 
i 
  
  
  
  
  
  
| Orthorectfication for every aerial image | 
| Create stereo photo-pair models | 
  
Y 
Seam lines among adjacent stereo photo-pair models 
are chosen 
| 
Construct valid mosaic polygon for every photo-pair 
model 
| 
| Left and right orthoimages are separately moasicked | 
i 
Right(left) mosaic 
orthoimage : 
  
  
  
  
  
  
  
  
  
  
  
  
Y 
Left(right) mosaic 
orthoimage 
  
  
| Parallaxes introduction À 
: 
| Stereomate aJ 
| 
| The measurable seamless stereo model | 
  
  
  
  
  
  
  
  
= Stereoscopically display, roam and measure i 
  
Figure 2. The generation procedure of the measurable seamless 
stereo model 
After the above steps, a moasic orthoimage and a mosaic 
steromate are produced and they can be used to form a seamless 
stereo model, which covers the whole block. The stereo model 
has been absolute oriented (geo-referenced). Some operations 
such as displaying, zooming, roaming and stereoscopic viewing 
can be implemented using the stereoscopic device. However, it 
order to perform accurate 3D measurement, the linage of each 
pixel is recorded as the metadata of the measurable stereo 
model. 
     
  
  
International Archiv 
BG ani Dit ut 
43. 3D measuremer 
The process for mez 
stereo model is illust 
The corresponding 
model (Manu: 
   
  
The pixel coordinate 
the orthoimag 
| 
The planemteric co« 
(X, Y) in the orth« 
  
  
di 
  
The 3D coordinat 
(X, Y, Z) 
  
Searching the original 
  
The left (right) ph 
  
  
coordinates (x , 
B [ 
L 
Figure 3. The 3D nx 
Item 
Principle dist: 
Photo scal 
Format 
Overlap 
Photo typ: 
Pixel size 
Average flight | 
Landform 
Data Rang 
  
Figure 4 shows the 
model generated fron 
mosaic polygons of 
Every stereo pair has 
measurable | seamles 
complementary colot 
Observed with red/gre 
surface points and ot