Accurate Measurement of Surface Grid Intersections From Close-Range Video Sequences

A novel approach for high-speed measurement of surface grid line intersection points across multiple video frames is described. Grids are printed or etched onto otherwise featureless surfaces for applications that include 3-D surface reconstruction, sheet metal surface strain measurement, and others. To achieve the necessary subpixel location accuracy, close-range imaging is used with data collected by a hand-guided digital video camera mounted on a portable articulated arm coordinate measuring machine. Grid extraction is based on ridge detection in a parallelized scale space, implemented with a 480-core graphical processing unit (GPU). The close-range narrow-depth-of-field focus variations within the video sequence are intrinsically handled by the scale space. Ridge linking, filtering, and parabola fitting are used to accurately extract the grid intersection points. While computationally intensive, experimental implementation using the parallel GPU hardware has achieved sustained throughput exceeding 15 frames per second, with more than 100 intersections extracted per frame. Experimental results are presented for both synthetically generated and actual video sequences.