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2.10 Other Components 
The system holds SPOT data in a unique internal 
format, but maintains all SPOT associated files. 
The system can ingest SPOT Panchromatic data 
and export files in the same format. 
3. RESULTS 
From some limited testing of the system the 
system has achieved sub pixel accuracy in 
image registration in ideal situations of low 
relief and plentiful matchable features, 
particularly arable farming scenes. In areas of 
greater relief change and much fewer 
matchable features the registration accuracy 
deteriorated to around 2 pixels. 
4. SYSTEM ISSUES 
4.1 Implementation of the System 
The PAIRS system built in an open architecture 
concept, using ENVI/IDL COTS software, and is 
hosted on a SUN platform using the UNIX 
operating system. The system architecture is 
based on a software package developed by Earth 
Observation Sciences Ltd called XPECT. 
XPECT is a visual programming environment in 
which modules (processes) are represented 
iconographically and visually strung together on 
a GUI to form chains which are processed. 
Chains can be saved, reloaded and modified. 
The modular design of the PAIRS system within 
XPECT results in a high degree of flexibility. 
All the procedures need not be run to produce 
an image registration. For example the Image 
Intensity process can be omitted if required. 
The XPECT environment is also ideal for 
experimental work, as chains can be modified 
and re-executed at will, allowing the operator 
to quickly optimize system parameters. 
5. FUTURE WORK 
The next phase of the PAIRS work will build on 
the work outlined in this paper. The major 
diference is that in addition to SPOT data, the 
system will process other optical data, 
including MOMS and IRS-1C. The image 
registration will also be cross sensor, so for 
example a SPOT image will be registered with a 
MOMS image. 
The system will also incorporate camera 
models two allow the generation of three 
dimensional coordinates and hence Digital 
Elevation Models (DEM). 
6. References 
Ackermann, F, 1984, Digital Image Correlation 
Performance And Potential Application In 
Photogrammetry, Photogrammetric Record 11 
p.429-439 
Maling , 1991, Coordinate Systems and Map 
projections for GIS, in Geographical Information 
Systems Vol.1 by Maguire D, Goodchild M, 
Rhind D. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996