Skeye was asked to generate a 3D mesh of the city centre of Basingstoke in the United Kingdom. Photogrammetry was selected as the methodology whereby the 3D geometry of objects can be derived from a series of overlapping aerial images. The images were captured using a dual camera system from a manned aircraft. Two cameras are mounted at an offset whereby one looks straight down and the second at an oblique angle of 40 degrees. Normally aerial imagery is flown in a series of parallel strips but with this camera system the data is captured in flying a circular pattern. This enables the oblique camera to view objects from all different sides. For the 3D generation of a mesh it is important to capture imagery of the facades as well as the straight down images. The average resolution of the images was 6 cm.
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In total 900 images were captured that were used for the modelling in combination with ground based measurements with a GPS. The photogrammetry method will derive a 3D coordinate (X, Y and Z) for as many image pixels that are recognised in adjacent overlapping images. The result is a very dense cloud of points with around 100 points per square meters. A small amount of noise cleaning was required to create a clean and crisp 3D mesh.
The dense point cloud was used to create a 3D mesh. In this process the points are joined in such a manner as to create triangles. These triangles are subsequently coloured with the imagery. The end result was checked with independent ground measurements and demonstrated an average accuracy of 4cm.