The Reconnection of Contour Lines from Scanned Color Images of Topographical Maps Based on GPU Implementation

This paper presents a method for the reconnection of contour lines from scanned color images of topographical maps based on graphics processing unit (GPU) implementation. The extraction of contour lines, which are shown with brown color on USGS maps, is a difficult process due to aliasing and false colors induced by the scanning process and due to closely spaced and intersecting/overlapping features inherent to the map. First, an effective method is presented for contour line reconnection from scanned topographical maps based on CPU. This method considers both the distance and direction between the two broken points of the contour lines. It gets better performance and has high connection rate, but the time complexity of the algorithm is nonlinear with the increasing size of topographical map. Second, the advantage of the massively parallel computing capability of GPU with the compute unified device architecture is taken to improve the algorithm. Finally, a better performance has been achieved based on the open source computer vision library. The experimental results show that the GPU implementation with loop-based patterns achieves a speedup of 1360× and the identical result compared with the implementation on CPU.