Addition of GCPs also increased the elevation accuracy of resultant DEMs (when compared to check data) with residual RMS of 0.50m (model 1, 5 GCPs) reducing to 0.22m (model 10, 50 GCPs), a value that approaches the accuracy of the lidar-only DEM (0.14m) and is better than that predicted (Lane and others, 2000).