Presentation given at Phnom Penh Mapping Meetup, 26 February 2013

1. Digital Elevation Models
and Relief Shading
Bernd Eversmann
Royal University of Agriculture
Faculty of Land Management and Land Administration

2. Contents
What is a DEM? How are DEMs generated? Accuracies you can expect
What can DEMs be used for? Tools for relief shading

3. What is a DEM?
A digital elevation model is a digital model or 3D representation
of a terrain's surface (wikipedia.org)

4. How is a DEM generated?
RADAR Interferometry with 2 receivers, 60m apart
A) From airborne or
satellite remote sensing:
Stereo images, RADAR or
LIDAR data are used in a
semi-automated process
to create a DEM.
Airborne Laserscanning or LIDAR

5. How is a DEM generated?
B) From terrestrial measurements with precise land survey
instruments. These spot measurements are then interpolated into
an elevation surface. With this method, it is costly and time-
consuming to cover bigger areas.

6. DEM, DTM and DSM...
Source: wikipedia.org

7. DEM, DTM and DSM...
Digital Surface Model Digital Terrain Model
Digital hillshade models generated from a Lidar scan.

8. What are DEMs used for?
Orthophoto production and topographic mapping
A DEM is needed for orthorectification of
an image, the process of removing the
effects of sensor tilt and relief to obtain a
photographic map with uniform scale.

9. What are DEMs used for?
Flood modeling

10. What are DEMs used for?
Visibility analysis

11. What are DEMS used for?
3D representations

12. A comparison of DEMs
ASTER GDEM v2 1) SRTM v3 1) Geoeye 2)
Data source ASTER Satellite Space shuttle radar Geoeye Satellite
Generation and
METI/NASA NASA/USGS Digitalglobe
distribution
Release year 2011 2003 ~ n/a
2000 - 2010
Data acquisition period 11 days (in 2000) n/a
(1.514 million scenes)
Posting interval 30m 90m 2m
Vertical accuracy
7 - 14m 5 - 10m (~4m f. 1-arcsecond data) <= 1.5m
(RMSE)
DEM coverage 83 degrees N ~ 83 degrees S 60 degrees N ~ 56 degrees S n/a
Areas with no ASTER data due to
Topographically steep area
Area of missing data constant cloud cover (supplied n/a
(due to radar characteristics)
by other DEM)
Vertical accuracies depend on land cover, slope angle and aspect (mainly
SRTM), number of stacked stereo pairs (Aster), availability of precise GCP
and other factors.
1) figures taken from: http://www.jspacesystems.or.jp/ersdac/GDEM/E/2.html and A. K. Karwel, I.
Ewiak (2008): ESTIMATION OF THE ACCURACY OF THE SRTM TERRAIN MODEL ON THE AREA OF
POLAND
2) Paradella, W.; Cheng, P.: Automatic DEM Generation – Using Geoeye-1 Stereo Data in Mining
Application; in Geoinformatics, Vol. 16, 01-2013, p. 10-12

13. Vertical Accuracy
NED 1) vs. SRTM Differences
1) The National Elevation Dataset (NED) is the primary elevation data product of the USGS. It is a
seamless dataset with the best available raster elevation data of the United States.
Source: http://topochange.cr.usgs.gov/assessment.php

14. Absolute Vertical Accuracy
SRTM and NED vs. GPS Benchmarks
Source: http://topochange.cr.usgs.gov/assessment.php

15. Crafts
Cartography
Art Science

16. Hill Shaded Maps
Eduard Imhof (1895 – 1986) , Prof.
of Cartography at ETH Zurich.

17. Hand-drawn vs. digital Relief
Problems in smaller scales, example Cambodia
Hand-drawn relief from CIA archives SRTM digital shaded relief

18. Relief Shading – digital vs. manual
Shaded relief at 1:1,000,000. Left: Federal Office of Topography swisstopo
(DV033492.2). Middle: from raw SRTM data. Right: from SRTM data
generalized with Terrain Sculptor. (Cartographic Perspectives, No. 67, p.52)

19. Relief Shading – digital vs. manual (2)
Shaded relief at 1:15,000,000. Left: Swiss World Atlas 2008. Middle: from raw
GTOPO30 data. Right: from GTOPO30 data generalized with Terrain Sculptor.
(Cartographic Perspectives, No. 67, p.52)

20. Filtered digital relief shading
Adjustment of visible Ridges
More information: http://www.terraincartography.com/terrainsculptor

21. Filtered digital relief shading
Increasing Valley Depths
More information: http://www.terraincartography.com/terrainsculptor

22. Links
Everything on shaded reliefs (techniques, software, ...)
http://reliefshading.com/
http://shadedrelief.com/
Software tools and publications on digital relief shading:
http://cartography.oregonstate.edu
Aster GDEM v2:
http://asterweb.jpl.nasa.gov/gdem.asp
SRTM v4:
http://srtm.csi.cgiar.org/

23. Thank you!