1. Information Session: October 12, 2011 – 2:30 – 4:00 in Rm. 7-150

2. Interdisciplinary Field School to Peru June 2012
For information, contact:
Dr. Catherine Nolin or Scott Emmons 2

3. Digital Elevation Models (DEM) / DTM
Uses in remote sensing: queries and analysis, 3D visualisation, layers in classification,
Fogo Island, Cape Verde Republic ASTER DEM / image
Banks Peninsula, Christchurch, New Zealand

4. DEM sources – where do they come from ?
Almost all DEMs have been created from remote sensing:
a. DEMs from digitising contours (e.g. NTDB)
The earliest were created by digitising contours on maps into layers
stereo photos -> contour lines -> digitised lines -> interpolate to raster grid
Arcmap: topo 2 raster PCI geomatica: vdemint

5. DEM data sources b. Digital Stereo photogrammetry: (e.g. BC TRIM)
Mass points captured from aerial photographs
stereo photos -> mass points -> interpolate to raster grid

6. TRIM DEM – masspoints ~70m spacing captured onscreen from stereo-photography ‘soft copy’
Created from mass points and break lines Aerial Photography (1:70,000)

7. BC TRIM DEM Interpolated to 25m grid By 1:250,000 map sheets
(100 tiles assembled together)
Vertical accuracy to within 10m
16 bit codes,
-9999 for invalid numbers
e.g. across border into AB

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

9. Post 2000 methods c. Direct image grid DEM data from imagery
RADAR e.g. Shuttle Radar Topographic Mission (SRTM)
Stereo digital satellite imagery (adjacent satellite tracks)
Issues: cloud cover and missing data
ASTER SPOT

10. DEM - layers a. Elevation
DN = (metres, 16 bit):  represented as grayscale or pseudocolour tints;
DEMs are stored as integer elevations (metres) or 32 bit (after interpolation)
some (NTS) DEM tiles in Canada may still be in feet
(how would the values compare ?) …. conversion = .3048

11. b. Shaded relief (hillshade)
A cartographic layer, DN= (relative amount of light reflected),
as grayscale; light source can be selected, usually from the NW.
High values on NW facing slopes, low values on SE facing slopes.
Select light source azimuth and angle
Default = 315, 45
useful for detecting errors and assessing quality

12. DEM grid displayed as grayscale Hillshading (NW light source – 315, 45)

13. BC provincial DEM 1985 (1981-1989) – Homathko Icefield - mapplace
BC provincial DEM 1985 ( ) – Homathko Icefield - mapplace.ca or lrdw.ca
Errors from lack of contrast in snowfields = few data mass points

14. 1 metre hillshaded DEM … from contours

15. c. Slope Calculated in degrees (0-90) or % (0 -> infinity)
slope is rise/run = vertical change over the horizontal distance
8 bit results should be adequate for most purposes

16. 4. Aspect
The direction in which a slope is facing, measured by azimuth (0-360)
This raises three questions for analysis:
north facing slope has both extreme values, 0 and ******
flat slopes have no value (they are given an arbitrary numerical value, e.g. 555)
0-360 requires 16 bit data; some software (PCI) converts to 8 bit by dividing by 2

17. 5. Incidence
Image data look similar to shaded relief, but with values 0-90
the angle (degree) of light incidence, based on the sun position at time of scene capture.
Requires knowledge of sun elevation and azimuth for the scene = metadata

18. 6. Second derivatives: slope concavity and convexity, used in generating watersheds and also viewsheds using line of sight

19. 7. 3D perspectives / fly-throughs
e.g. Google Earth etc..

20. 8. Anaglyphs St-Pierre – Miquelon SRTM DEM

21. Klinakline Glacier, south Coast Mountains (ASTER DEM)

22. DEMs in Digital Image Classification
Land Cover Classification Using IRS LISS III Image and DEM
in a Rugged Terrain: A Case Study in Himalayas
Green
Red
NIR
MIR
NDVI
DEM

23. Next lecture: DEMs available
A DEM is a continuous grid of elevation values –
one height value per pixel ….. in a channel (not a band)
AGENCY  SCALE  RESOLUTION (metres)
Municipal  1: 2,  
Provincial  1: 20,000   
Federal  : 50,  
Federal  : 250,000   
Global  : 1,000,000   
Download Canadian data from geobase.ca (1:50,000 / 1:25,000)
* BC is provincial data (25m) resampled for NTDB (50m)