Conventional orthorectification software cannot handle surface occlusions and image visibility. The approach presented here synthesizes related work in photogrammetry and computer graphics/vision to automatically produce orthographic and perspective views based on fully 3D surface data (supplied by laser scanning). Surface occlusions in the direction of projection are detected to create the depth map of the new image. This information allows identifying, by visibility checking through back-projection of surface triangles, all source images which are entitled to contribute color to each pixel of the novel image. Weighted texture blending allows regulating the local radiometric contribution of each source image involved, while outlying color values are automatically discarded with a basic statistical test. Experimental results from a close-range project indicate that this fusion of laser scanning with multiview photogrammetry could indeed combine geometric accuracy with high visual quality and speed. A discussion of intended improvements of the algorithm is also included.
Abstract. The now widely available and highly popular among non-expert users, particularly in the context of UAV photogrammetry, Structure-from-Motion (SfM) pipelines have also further renewed the interest in the issue of automatic camera calibration. The well-documented requirements for robust self-calibration cannot be always met, e.g. due to restrictions in time and cost, absence of ground control and image tilt, terrain morphology, unsuitable flight configuration etc.; hence, camera pre-calibration is frequently recommended. In this context, users often resort to flexible, user-friendly tools for camera calibration based on 2D coded patterns (primarily ordinary chessboards). Yet, the physical size of such patterns poses obvious limitations. This paper discusses the alternative of extending the size of the calibration object by using multiple unordered coplanar chessboards, which might accommodate much larger imaging distances. This is done initially by a detailed simulation to show that – in terms of geometry – this could be a viable alternative to single patterns. A first algorithmic implementation is then laid out, and results from real multi-pattern configurations, both ordered and unordered, are successfully compared. However, aspects of the proposed approach need to be further studied for its reliable practical employment.
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