Given the center GPS coordinate and radius of a circle area, it crawls the Google Street View data, including panorama image, depth map and the transformation panoramas

• GetPanoramaMetadata: parse the panaorama meta data given panoid or GPS coordinate
• PanoramaMetadata: parse panorama map and depth map

• depth_map: decode the depth map to (x, y, d) representation
• point_cloud: generated point cloud given panorama image and depth map
• gen_bfs_tree: breath-first search on panorama graph (each node is one paranoma)
• post_order_traverse: merge paranoramas into one large point cloud