1. Warm-up slide
Jan : end of The World: Dubai island development sinks back into sea - financial crisis

2. Digital Elevation Models (DEM)
Digital Terrain Models
(DTM)
Digital Surface Models
(DSM)
All DEMs are created from remote sensing !

3. Applications in digital image processing:
Inclusion in queries and analysis
Inclusion as layers in classification
Feature extraction via topographic effects
3D modelling and visualisation

4. Extended list of DEM uses
Extracting terrain parameters
Modeling water flow or mass movement
Creation of relief maps and models
Rendering of 3D visualizations
Rectification of aerial photography or satellite imagery
Reduction (terrain correction)
Terrain analyses in geomorphology and physical geography

5. Early DEM generation: pick regular points or digitise contours

6. DEM data formats Discrete elevation data
Contour lines – from maps or digital files
Mass points …. and break lines
These are interpolated into GRIDS (PCI etc..)
B. Continuous DEM data
Triangulated Irregular Networks (TIN)
Raster grids – for remote sensing … ideally ~same pixel size

7. Evolution of DEM creation
1950s Generation of contours from stereo photos
1980s Mass points from stereo photos
1990s Automated generation of masspoints
2000s Direct generation of grids from stereo-imagery
(and expansion of LiDAR)

8. DEM sources: global GTOPO30 ~1993 1km digitising of 1:1,000,000 world maps – contours -> grid

9. DSM sources 2000+
Shuttle Radar Topographic Mission (SRTM) Feb m
download by 5 x 5 degree lat/long tile N – 56S

10. ASTER m
microns

11. ASTER Global DEM (2009) data from 1999-2008
30m download x 1 degree

12. ASTER Global DEM : Kananaskis Park area DEM and #scenes used

13. BC TRIM DEM 25m raster grid
Created from mass points and break lines Aerial Photography (1:70,000)

14. TRIM DEM – masspoints ~70m spacing captured onscreen from stereo-photography ‘soft copy’ (prior to fully automated image matching)

15. TRIM DEM 1998 Interpolated to 25m grid By 1:250,000 map sheets
(100 tiles assembled)
Vertical accuracy to within 10metres
UTM pixel coordinates to even 25m,
edges to round 100m
Continuous surface
16 bit codes,
-9999 for invalid numbers
e.g. across border into AB

16. Federal v Provincial DEM sources
BC TRIM: 25m grid 1980s
Federal: mostly from digitised contours except BC
BC: is TRIM DEM resampled to 50m pixels
Canada NTDB: (by E / W 1:50,000 map sheet)
1:50, m pixels
1:250, m
Data are mostly stored / downloaded in Geographic (lat/long)

17. DEM data processing – PCI or ArcGIS
Data are usually stored in Geographic tiles (lat/long)
Download or transfer data tile(s)
Mosaic as needed (and maybe clip)
Reproject e.g. Albers, UTM … and ….. resample to match imagery
(avoid nearest neighbour for resampling)
Clip to area / imagery
Generate shaded relief to assess quality / problems

18. DEM grid (.tif format or ESRI grid) displayed as grayscale elevation in metres Hillshading (NW light source – 315, 45)

19. DEM products Elevation 0- ~9,000 (earth) 16 bit (0-63,356)
Shaded relief
Slope (if in degrees)
Aspect bit (flat = ?)
Incidence requires orbital metadata
Visual: Anaglyphs and 3D perspectives

20. SPOT DEM: m

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

22. Photogrammetry: Tatras, Slovakia 2m

23. LiDAR 10cm – 10m (Mt.St. Helens)