| Popis: |
This paper evaluates and discuses the accuracy of laser scanner in DTM (digital terrain model) generation in forested and suburban areas. Special emphasis is laid in order to optimize the selection of ground hits used for the creation of the DTM of future high-pulse-rate laser scanners. A novel DTM algorithm is depicted in detail. The algorithm is based on five phases: (1) calculation of the original reference surface, (2) classification of vegetation and removal of the vegetation from the reference surface, (3) classification of the original cloud of points using the reference surface, (4) calculation of the DTM based on the classified ground hits, and (5) interpolation of the missing points. Standard error of 15 cm was obtained for flat forest areas and the error increased with increasing terrain slope to the value of approximately 40 cm at the slope of 40%. The average standard error for forest area was slightly better than 25 cm. The laser-derived DTM of the forest road deviated only 8.5 cm from the true height. An optimum performance for the DTM generation was obtained by averaging the ground hits which located, at the maximum, 60 cm above the minimum terrain values. A simplified algorithm was suggested for more operational use based on the first pulse mode data. Special cases of the suburban area DTM were verified including terrain heights below the buildings and bridges, terrain heights of roads, terrain heights below large outdoor light fixture, to name but a few. About 100 special cases in suburban/urban environment for DTM verification were searched. The corresponding standard error between the laser-derived values and reference data was 45 cm. |
