1. A road-model-definition system suitable for an automated-vehicle, said system comprising: a lidar-unit suitable to mount on a host-vehicle, said lidar-unit used to provide a point-cloud descriptive of an area proximate to the host-vehicle; and a controller in communication with the lidar-unit, said controller configured to select ground-points from the point-cloud indicative of a travel-surface, tessellate a portion of the area that corresponds to the travel-surface to define a plurality of cells, determine an orientation of each cell based on the ground-points within each cell, divide a cell when a height-deviation from a plane of the cell by the ground-points within the cell is greater than a deviation-threshold, combine adjacent cells when planes of the adjacent cells are parallel within a parallel-threshold, designate a cell as a finalized-cell when the deviation from the plane of the cell by the ground-points within the cell is not greater than the deviation-threshold and the cell is not parallel to any adjacent cell within the parallel-threshold, define the road-model of the travel-surface based on the orientation of finalized-cells when all cells are characterized as finalized-cells, and operate the host-vehicle in accordance with the road-model.