5. EFFECTS ON PHOTOGRAMMETRIC WORKFLOWS

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5.1 Increasing Image Overlaps

An essential paradigm shift in aerial and terrestrial mapping results from vanishing variable costs per image. Along a flight line, increasing the overlap from traditional 60% to novel 90% is absolutely cost-free, but increases the number of images by a factor 4. Across the flight direction, additional flight lines are needed to go from 20% to 60% side-lap, but the associated cost is only for air time, not for the imagery itself. Going from 20% to 60% increases the number of images again by a factor of 2.

 

Transiting from 60/20 to 90/60 provides an increase in redundancy by nearly an order of magnitude.  To use this increase the workflows must be sufficiently automated to eliminate any variable labor per image.

 

5.2 Smaller Ground Sampling Distances

Since the number of images no longer affects the project cost, one can think differently about pixel size. The choice of a ground sampling distance GSD is driven by the need to map certain detail, and also to ensure that automation succeeds. In urban mapping one might have relied on scanned film with a GSD at perhaps 20 cm. With digital cameras one might want to go to 8 cm to obtain flawless dense digital surface models with clearly delineated roof lines, gutters, chimneys, skylights, sidewalks and street details.

 

A film project for a 150 km2 urban  area at 20 cm pixels had previously been done with 150 aerial film images at 60/20 overlaps. It now may be done at 90/60 overlaps at a pixel size of 10 cm, resulting in 3,000 digital images.

 

5.3 Full Automation

The age-old dream of fully automated aerial triangulation, orthophoto- and DSM-production has become a reality due to higher overlaps and smaller pixel sizes. High overlaps support a “super-resolution” since every terrain point is imaged 10 times and this redundancy removes the noise in the resulting measurements. A DSM no longer is created at postings at 10 times the pixel size, but now at a single pixel spacing. The idea of “dense matching” has arrived (Klaus, 2007).

 

5.4 Color and False Color Infrared

A stark difference between traditional film and current digital imaging is the ubiquitous availability at no variable or fixed extra cost of an infrared image channel. This has led to strong advances in 3D mapping, which has a perennial issue with occlusions by vegetation. Vegetation can be mapped with infrared color.

 

5.5 Urban 3D Modeling

The crux of urban 3D-modeling is the cost per building, and the level of detail. Dense matching at each pixel and semantic interpretation of scene contents make 3D building models affordable and cause a surge in interest and applications. As stated before, full automation of façade- and roof-maps relies on high image overlaps, use of simultaneous 4 or 5-color bands and small pixel sizes (Zebedin et al., 2006; Leberl et al., 2012; Bimber, 2010).