1. Digital Elevation Models (DEM) Digital Terrain Models (DTM) / Digital Surface Models (DSM) Brief Review
Applications in image processing:
Inclusion in queries and analysis
Inclusion as layers in classification
Feature extraction via topographic effects
3D modelling and visualisation

2. DEM data formats A. Discrete data
Contour lines – from maps or digital files
Mass points …. And break lines
terms:
These can be interpolated into GRIDS (PCI etc..)
Method of interpolation can have high impact on the DEM
B. Continuous data
Triangulated Irregular Networks (TIN)
Raster grids –needed for remote sensing – should be ~same pixel size

3. DEM sources: global GTOPO30 ~1993 1km

4. DEM sources Canada NTDB: 1:50,000 1950-90 25 – 100m pixels
Aerial photography > m
Municipal  : 5,000   (usually contours)
BC TRIM :20, s photogrammetry
TRIM II breaklines
Landsat MSS :250, Satellite path overlap
Landsat TM/ETM 1:100, Satellite path overlap

5. DSM sources 2000+
Shuttle Radar Topographic Mission (SRTM) Feb m

6. ASTER – 25m
microns

7. SPOT DEM: m

8. Directed high res sensors- Ikonos 1999 2-5m

9. LiDAR 10cm – 10m (Mt.St. Helens)

10. Photogrammetry: Tatras, Slovakia 2m

11. Anaglyph - Malaspina

12. DEM products Elevation 0- ? 16 bit (signed) Shaded relief 0-255
Slope (if in degrees)
Aspect bit
Incidence requires orbital metadata
Visual: Anaglyphs and 3D perspectives

13. DEM quality and errors Scale – Match with needs and imagery
Type of terrain - pixel homogeneity
Horizontal and vertical accuracy
DSM or DTM ?
Interpolation / resampling method – from points or lines?
Null values and spikes
Errors are more easily spotted from a hillshaded model

15. BC provincial DEM 1985 (1981-1989) – Homathko Icefield - mapplace
BC provincial DEM 1985 ( ) – Homathko Icefield - mapplace.ca or lrdw.ca

16. Assiniboine Spillway, MB

17. SRTM – ASTER comparison Sample area in Indonesia

18. Paper to review for next week