A simple accuracy assessment has been performed by 
comparing the building height derived from single IKONOS 
image using the software with that derived from a stereo pair of 
aerial photograph 1:10000. The azimuth and elevation angle of 
the satellite and the sun of the image for monoplotting are listed 
in table 1. The IKONOS image of the test site is shown in fig. 8. 
The height of the buildings derived from stereo aerial photos is 
labelled in yellow. DEM of 90m/pixel resolution is applied. The 
3D geometry of the objects extracted from the satellite image 
with the software is compared to that generated with the stereo 
pair of aerial photos. 51 samples have been compared, with the 
largest disparity in height of 10m and smallest of 0.2m. The rms 
for the height of the objects is about 2m, while the accuracy in 
map coordinates is also about 2m. 
TABLE I. The azimuth and elevation angles of the satellite and the sun 
of the IKONOS image 
a 
A 
a' 
A' 
Image 
192.9323 
72.96125 
125.6500 
60.2592 
7. CONCLUSION 
The new method for monoplotting is described. It reduces the 
measurement from 2 dimensions to 1 dimension, thus increase 
the accuracy in height measurement. It combines methods using 
both the base and shadow information to suit different situations. 
Therefore, whenever one base point or shadow edge of the 
vertex of the building top is clearly located in the image, the 3D 
flat building can always be reconstructed. 
long shadow; iv) small elevation angle of the satellite to have 
long length of top to base; and v) the coarse density of the 
objects to avoid overlay the shadow on top of nearby objects. 
The method has been implemented in a standard PC system. A 
software suite for realtime 3D reconstruction and visualization 
has been established. 
There are several areas for future work, such as to extend 3D 
modeling for some slope roofs or non-flat roofs. We hope 
accomplish these in the next version of the software suite. 
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ACKNOWLEDGEMENTS AND APPENDIX (OPTIONAL) 
Funding support for this project is provided by the Agency for 
Science, Technology and Research (A*STAR), Singapore.