* manually selection of four control point pairs in well 
distributed pattern to define a similarity transformation 
parameters between the map and image which are used to find 
the rotational differences to alter each edge pixel gradient 
direction. 
the same four control point pairs selected to alter edge 
pixel gradient direction are also used for an initial 2D 
transformation for the matching between the map and the 
image. 
Abbasi-Dezfouli and Freeman (1994) described a method of 
chain coding using shape, size and relative geometry of 
patches to distinguish correctly matching patches from a 
pair of SPOT images without using any ground control 
points or ephemeris data. The same method can be applied 
for registration of image to map to select a set of well 
distributed polygons which will then be the input to the fine 
matching algorithms discussed above. This method will 
allow the removal of manual the component of selecting 
control points from the system. Some initial results for this 
method using aerial photographs are reported by Dowman et 
al, (1996) at this congress. 
The buildings have shown large residuals on the matched 
points due to perspective distortion of the buildings. These 
are systematic displacements which are related to the camera 
look angle and the orientation of the buildings. It is 
necessary to remove the systematic errors first from the 
matched points, which will then allow a better accuracy of 
registration of image to map. 
For full absolute arientation and the removal of perspective 
distortion height information is required. This aspect has 
also been discussed in Dowman et al, (1996). 
6. FUTURE WORK 
Future work is concerned with developing algorithms which 
can replace the manual components of the semi-automatic 
system and convert it into fully automatic system for the 
registration of image to map. The system will incorporate 
different types of sensor data, multi-resolution data and 
different landcover types will also be considered to make the 
system robust. The system will also include a model of the 
distortion which will identify and remove the perspective 
effects. 
ACKNOWLEDGMENTS 
Acknowledgment is made to the Space department, DRA, 
Farnborough, UK who supplied the DDS High Resolution 
satellite data and the height of buildings of the Farnborough 
test area as a part of a DRA contract. Authors also feel 
grateful to the The Natural Environment Research Council 
for providing a research studentship for the development of 
a fully automatic image to map registration system. 
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