We present a preprocessing method for automatic break line detection. Our method is given a set of edges (break lines and non-break lines) we eliminate the non-break line edges leaving only those with higher probability of being break lines. Our method is based on fusing IR images and LiDAR cloud points. In the first step, we apply the Canny edge detection algorithm to the IR images (producing a superset of break lines). Then we project the LiDAR points onto a 2-D plane, ignoring the set of points that are greater than a selected threshold (different elevation thresholds have been selected), which allows the footprints of some elevated structures to appear clearly in the set of projected points. Those structures that appear in both LiDAR points and IR images are used as references for registration of LiDAR cloud points with the IR images. After registration, we eliminate all the edges that appear in flat areas, which is achieved by applying a 3D filter to the LiDAR points.