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, define a road-model of the travel-surface based on the orientation of the cells, and operate the host-vehicle in accordance with the road-model.