This paper presents a method to detect reflection with 3D light detection and ranging (Lidar) and uses it to map the back side of objects. This method uses several approaches to analyze the point cloud, including intensity peak detection, dual return detection, plane fitting, and finding the boundaries. These approaches can classify the point cloud and detect the reflection in it. By mirroring the reflection points on the detected window pane and adding classification labels on the points, we can have improve the map quality in a Simultaneous Localization and Mapping (SLAM) framework.