Full text: XVIIIth Congress (Part B3)

  
   
  
  
   
   
   
   
    
   
    
   
    
  
   
    
  
   
  
  
   
  
  
   
   
  
The visualization of the data was performed by 
generating a sequence of perspective views. Figures 
4 and 5 show perspective views of the "draped" 
surface data, including a scene with various terrain 
and building structures and another one of less 
complexity. Note, that the side of the man-made 
structures are only shaded but not painted. 
    
Figure 5. Perspective view of a less complex area 
Silver Spring project 
The DTM extraction for the Silver Spring site 
differed from the Manhattan area in a number of 
ways. The scale of the photography was larger, but 
more importantly, the terrain itself included 
wooded, suburban areas with single family housing 
units. Figure 6 shows the project area. 
In dividing the project area into subsites, we had to 
carefully consider the differences between the 
characteristics of the suburban and downtown 
sections and decide which special strategies to apply 
(Helava, 1988). The critical issue in suburban type 
areas was to come out with a DTM strategy that 
would give "true" ground elevations in open areas 
while simultaneously yielding house rooftop 
elevations at the same time. Such a solution would 
immediately provide deliverables, i.e., the combined 
surface of natural and man-made objects. After 
performing several tests on typical areas, we 
selected the optimal automated DTM strategy for 
our objective, with the understanding that in wooded 
areas we would not obtain "true" ground elevations 
but elevations of treetops and bushes instead. Only 
prominent building structures in these areas would 
have their rooftop elevation digitized using feature 
extraction techniques. 
866 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996 
  
F igure 6. Silver Spring project area 
The downtown DTM area was generated in the same 
fashion as in the Manhattan project, where "true" 
ground elevations, without buildings, trees, and 
other obstructions were determined using multiple 
DTM editing tools. An initial 4m grid spacing was 
used to generate DTMs for the two downtown sites. 
Figure 7 shows a perspective view of the data 
including a single family housing area. The front of 
the image shows clearly the performance of the used 
DTM strategy. The rooftops rise out from the rolling 
surface of trees and bushes while the open areas 
such as the road in the center follow the terrain. 
gsm 
Figure 7. Silver Spring, suburban area 
  
    
    
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