3.4 Ortho compositing 
Once all pixel information in the ortho image mosaic is known, 
it is necessary to blend them together in order to create a visual 
appcaling result. Although project-based colour balancing is 
applied to the input images, a final smooth blending is still 
necessary. For smooth blending of the tile patches, we use the 
proposed method by Uyttendaele et al. (Uyttendaele, Szeliski, & 
Steedly, 2011). They presented a technique for fast Poisson 
blending and gradient domain compositing. 
4. PROCESSING ENVIRONMENT 
Since the UltraMap v3 processing pipeline is very resource 
intensive, our approach offers support for different processing 
environments. On the one hand side, the complete DSM/ortho 
pipeline can be processed on scalable CPU-only machines, and 
on the other hand side the dense matching can also run on 
dedicated GPU nodes. The latter delivers high speed-ups 
because the dense matching is best suitable for a SIMD 
architecture such as graphics cards. Figure 4 shows a potential 
configuration of an UltraMap v3 system. The newly introduced 
V3 machines (which are resource intensive machines) strive for 
high performance, since an entire machine can be used to work 
on one task at a time. The existing V2 machines share their 
processing power with different tasks running on the same 
machine. The V3 machines can either be configured as CPU- 
only or as GPU-enabled nodes. 
The front-end machine is used to interact with the data and is 
not designed for processing. A very import part of the 
processing environment is the network which is required to 
transfer the data most efficiently between processing nodes and 
disk storage. 
  
  
Front-end 
  
  
  
  
Figure 4 Example for the UltraMap v3 processing environment. 
5. VISUALIZATION AND INTERACTION 
5.1 DragonFly Technology 
Since the beginning of UltraMap, DragonFly is the technology 
which is used to interact with large amount of UltraCam image 
data (Reitinger, Hoefler, Lengauer, Tomasi, Lamperter, & 
Gruber, 2008). 
DragonFly is based on a technology called Seadragon which is a 
Microsoft technology also built-in into other products (e.g. 
DeepZoom, Zoom-It, or Photosynth). For UltraMap v3, we 
introduce some more extensions and enhancements of the 
existing DragonFly technology. On the one hand side, we 
worked on optimization and improved user experience in order 
to have a smooth rendering of the processed ortho tiles. On the 
other hand side, we are able to exchange image content on the 
fly. This is required for any modification on the image data (i.e. 
modifying the DSM/DTM or the contribution mask). 
The ortho application which is the main user interface for 
working with ortho data uses DragonFly for visualizing all data 
generated. By exploiting shader code on the graphics card, we 
are able to interactively blend between the DSMOrtho and the 
DSM. This allows for quick quality controls and data 
interpretation while evaluating the quality of the dense matching 
result. The shader is also used to control the final radiometric 
tone of the image block. Another feature of using shader code is 
to do relief shading based on DSM data (Figure 5). 
    
Figure 5 On-the-fly relief shading of a generated DSM which is 
one feature of the DragonFly technology (data courtesy of 
Ordnance Survey, UK). 
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