A NEW APPROACH FOR GENERATING A MEASURABLE SEAMLESS STEREO 
MODEL BASED ON MOSAIC ORTHOIMAGE AND STEREOMATE 
Mi Wang 
State Key Laboratory of Information Engineering in Surveying Mapping and Remote Sensing (LIESMARS) 
Wuhan University 430079, China - wangmi(@x263.net 
  
KEY WORDS: Aerial Photogrammetry, Digital Orthoimage, Stereoscopic Model, Measurement, Accuracy 
ABSTRACT: 
Digital orthoimage (or orthophoto) is a type of information-rich digital products and has found applications in many fields. However, 
digital orthoimage itself is a 2-dimensional product and therefore it is insufficient for many applications. On the other hand, the 
traditional stereo model of photogrammetry formed from a pair of overlapping aerial photographs offer the possibility of both 3D 
measurement of terrain surface and terrain objects. However, it cannot be used a plan like the case of digital orthoimage and the model 
size is usually limited to the stereo pair. To take the advantage of both, the concept of stereomate was introduced by Collins in 1968. It 
is a new image with additional relief displacement. The total amount of relief displacement at each point of the stereomate is exactly 
the same as the sum of two relief displacements at the same position on both images of the stereo pair. That is, if this stereomate is used 
together with the orthoimage, one is still able to reconstruct a 3D surface of the area precisely. The main limitation with the current 
practice is that if more than one stereo pairs are used to generate the stereo orthophoto pair, the solution is not rigorous and thus leads 
to low accuracy of 3D measurement in highly mountainous areas although reasonable accuracy of 3D measurement can be achieved in 
areas with low relief. This paper introduces the concept of “measurable seamless stereo model”, which is formed by a mosaic 
orthoimage and a mosaic stereomate (i.e. mosaics of a whole block of aerial photographs), with the lineage (image coordinates on 
original photograph and the orientation parameters of the original photograph) of each pixel on both mosaic orthoimage and a mosaic 
stereomate recorded. Such a measurable seamless stereo model not only provides seamless 3D landscape environment but also offers 
the rigorous and thus accurate 3D measurement of any object and feature visible in the measurable scamless stereo model without 
explicit orientation procedure. Experimental results that the accuracy of 3D measurement from the “measurable seamless stereo 
model” proposed in this study is about 20 times higher than that from the traditional orthoimage pairs and is nearly similar with that in 
the original photo-pair model. 
1. INTRODUCTION 
Digital orthoimage (or orthophoto) is a type of information-rich 
digital products and has found applications in many fields, such 
as urban planning. However, digital orthoimage itself is a 
2-dimensional product and therefore it is insufficient for many 
applications (Blachut and van Wijk, 1970; Baltsavias, 1996) 
because it is a two-dimensional (2-D) representation of the 
3-dimensional (3D) terrain surface and terrain objects. A 
commonly used 3-dimensional representation of terrain surface 
is digital terrain model (DTM) but DTM has two limitations, Le. 
a lack of texture information for interpretation purpose and no 
representation of terrain objects. Also it is not possible to use 
DTM as a 2-D plan. On the other hand, the traditional stereo 
model of photogrammetry formed from a pair of overlapping 
aerial photographs offer the possibility of both 3D measurement 
and texture information for interpretation. However, it cannot 
be used a plan like the case of digital orthoimage and the model 
size is usually limited to the stereo pair. 
Indeed, it is very desirable to have a product which has the 
advantages of orthoimage (i.e. information-rich, possible for 
2-D measurement), stereo model (i.e. possible for 3D 
measurement) as well as DTM (i.e. 3D representation of a large 
area). 
It is noticeable that the stereomate introduced by Collins (1968) 
at the National Research Council (NRC) of Canada serves part 
of the purpose. The stereomate is a complementary image to an 
orthoimage. It is a new image with additional relief 
displacement. The total amount of relief displacement at each 
point of the stereomate is exactly the same as the sum of two 
relief displacements at the same position on both images of the 
stereo pair. That is, if this stereomate is used together with the 
orthoimage, one is still able to reconstruct a 3D surface of the 
area precisely. Simplicity and efficiency of using stereo model 
are of particular interest and value for many users (Blachut, 
1976). The idea was great and this promotes Sarjakoski (1990) 
to claim that digital stereo imagery can be taken as a map 
product in the future in practical applications. 
Different aspects and applications of stereo orthophoto pair 
were discussed (Blachut 1976, Collions and van Wijk, 1970). 
The 3D measurements from the stereo orthophoto pair have also 
been discussed (Kraus et al, 1979; van Wijk, 1979). It is 
noticeable that there are some limitations with the current 
practice of stereo orthophoto pair, i.e. 
e The extent of stereoscopic view of these stereo models is 
applicable only in the overlapping area of the photo pair, 
as the stereo orthophoto pair is still based on photo pair. 
e If more than one stereo pairs are used to generate the 
stereo orthophoto pair, the solution is not rigorous and thus 
leads to low accuracy of 3D measurement in highly 
mountainous areas although reasonable accuracy of 3D 
measurement can be achieved in areas with low relief. 
In practice, the area of interest often covers more than one 
stereo pair, therefore, a rigorous solution which will enable us to 
perform accurate 3D measurement from the stereo orthophoto 
pair of large area would be of great help (Wang, 2001; Li etats 
2002). Indeed, this paper aims to propose the concept of 
“measurable seamless stereo model”, which is formed by a 
mosaic orthoimage and a mosaic stereomate (i.e. mosaics of à 
  
   
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