1. A computer-implemented method for extracting level and reference grid information for a building interior from point cloud data, comprising: obtaining point cloud data, of the building interior, comprising laser scanning points of a building; organizing the point cloud data into a three-dimensional structure of voxels, the three-dimensional structure consisting of an X-axis, Y-axis, and Z-axis, wherein each voxel represents a value on a regular grid in three-dimensional space; generating an X-axis histogram by accumulating the voxels positioned along the X-axis of the three-dimensional voxel structure; generating a Y-axis histogram by accumulating the voxels positioned along the Y-axis of the three-dimensional voxel structure; generating a Z-axis histogram by accumulating the voxels positioned along the Z-axis of the three-dimensional voxel structure; extracting level information from the Z-axis histogram for an interior structure of the building interior; and extracting reference grid information of the interior structure of a floor plan for the building interior from the X-axis histogram and the Y-axis histogram, wherein peaks of the X-axis histogram and Y-axis histogram are used to identify a wall location or location marker of a reference grid.