The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B3b. Beijing 2008 
(a) (b) 
Figure6. (b)In IKONOS lm resolution image, an outline of a 
building is drawn in yellow, the lines from top to base in cyan, 
top to shadow in magenta, length of the lines is corresponding 
to height of 36m; 
(a) the 3D reconstructed building when height is 36m. 
(a) (b) 
Figure7. (b)Similar to fig. 6b; lines touch the base or shadow 
when height is 125m; 
(a) the 3D reconstructed building when height is 125m. Texture 
of the building matches the ground. 
©CRISP 
guidelines in magenta are from the building top to shadow. 
For example, when the building height is set to 36m as in fig. 6, 
the reconstructed 3D building is shown in fig. 6a. It is obvious 
that the guidelines do not reach the base or shadow edge (fig. 
6b), the 3D object is also out of position (fig. 6a), and part of 
the texture for the side of the building is still on the ground 
when the height is not accurate. As the user changes the height 
interactively, the length of the guidelines change accordingly, 
and the 3D object moves its position. Figure 7 shows the 
guidelines touch the base or shadow edge, the object moves to 
its exact location, and its texture matches the ground texture 
perfectly when the height is set to 125m. 
In the software, the guidelines from top to base, and top to 
shadow are drawn automatically with the change of building 
height. It is easy for the user to stop moving the mouse wheel as 
soon as the guidelines touch ground or touch shadow edge. The 
building height is thus set and 3D geometry is derived. The 
advantage of showing all the outlines to their base and shadow 
is that it enables the user to find the height even when there is 
only one base or shadow point seen clearly, and it also enables 
the user to choose the best match when more points are 
available. 
The software provides the reconstructed 3D models an instant 
view. When the outline of an object is drawn, the triangulation 
of the polygon will be performed to provide a set of triangles, 
vertices and texture coordinates. The software will re-calculate 
the vertices of geometric position and texture coordinates 
whenever the height of an object is changing. The facades of 
the object facing the satellite are also determined, therefore, 
they will dress on the texture from satellite image, while those 
away from satellite will be in gray. As a consequence, the 3D 
object, fully textured and rendered, is shown in the 3D viewer. 
This enables the user to have a visual inspection of the building 
feature in almost realistic 3D. The usual functionalities, such as 
zooming in and out, rotating and viewing in different angles, 
are also provided for the 3D views. 
5.3 Data Import, Export and Updating 
An important function provided is that existing 3D city models 
can be imported to this system for updating, and the new 3D 
models generated by the system can be merged and 
incorporated for later exportation to other systems. This system 
is currently able to import and export 3D models to ASCII 
format, which is compatible to Leica Photogrammetric Suite 
(LPS) and Socet Set ASCII format, and Shapefile format, which 
is a popular GIS format that most commercial software supports. 
Meanwhile, we have designed the internal format to memorize 
the coordinates of the objects in the satellite image as well. 
When the higher resolution of DEM is available, more GCPs 
are provided, or higher accuracy of RPC is provided, the 
software is able to update 3D geometry of the objects 
automatically. 
6. TEST SITE AND ACCURACY ASSESSMENT 
As mentioned above, the accuracy depends on the satellite 
acquisition and sun geometry. The larger the satellite elevation 
angle, the poorer the accuracy of 3D geometry; the larger the 
sun elevation angle, the poorer the accuracy of 3D geometry. 
For measurement of building heights, it is preferable to choose 
the image with smaller elevation angles. However, for the 
image ortho-rectification, which will be overlaid on top of 
DEM as ground texture, it is preferable to have an image with 
larger elevation angles.