Constructing 3d city models by merging aerial and ground views.

摘要: 52 November/December 2003 Published by the IEEE Computer Society 0272-1716/03/$17.00© 2003 IEEE and the zcoordinate the altitude. To process the scans efficiently, it’s helpful to resample the scan points to a row-column structure even though this step could reduce the spatial resolution. To transfer the scans into a DSM—a regular array of altitude values—we define a row-column grid in the ground plane and sort the scan points into the grid cells. The density of scan points is not uniform, which means there are grid cells with no scan point and others with multiple scan points. Because the percentage of cells without scan points and the resolution of the DSM depend on grid cell size, we must compromise by leaving few cells without a sample while maintaining the resolution at an acceptable level. In our case, the scans have an accuracy of 30 centimeters in the horizontal and vertical directions and a raw spot spacing of 0.5 meters or less. Measuring both the first and the last pulses of the returning laser light, we select a square cell size of 0.5× 0.5 meters, resulting in about half the cells being occupied. We create the DSM by assigning to each cell the highest zvalue among its member points to preserve overhanging rooftops while suppressing the wall points. We fill the empty cells using nearest-neighbor interpolation to preserve sharp edges. We can interpret each grid cell as a vertex, where the x, y location is the cell center and the zcoordinate is the altitude value—or as a pixel at x, y with a gray intensity proportional to z.