GEOG Mid term

Digital Elevation Models (DEM) - Terrain Models (DTM) A DEM is a continuous grid of elevation values - one height per pixel (grid cell) They are the modern equivalent of terrain previously stored in contour lines

Google Earth – 3D perspectives (and flythroughs)

DEM creation by digitising contours (e.g. NTS maps -> NTDB layer). This is 'second hand' digital, as contours are abstract stereo photos -> contour lines -> digitised lines -> convert to raster GRID (topo to raster)

DEM Grid

2. Digital stereo-photogrammetry: (e.g. BC TRIM) This is a better option, captured directly from aerial photographs stereo photos -> mass points -> convert to raster GRID (topo to raster)

Traditional method : stereo photos –> contours -> shaded relief Digital method: digital photos –> points –> DEM –> shaded relief and DEM <-> Contours Air Photo - DEM - Shaded relief This is the DEM – for data analysis

Ikonos 5m 3. Direct image grid DEM (> year 2000) Stereo digital satellite raster imagery Ikonos 5m

SRTM    (Shuttle Radar Topographic Mission): 90 metre pixels, 56ºS-60ºN

DEM sources: global GTOPO30 ~1993 1km http://edc.usgs.gov/products/elevation/gtopo30/gtopo30.html

LiDAR DEM - 2009

TYPICAL RESOLUTION (metres) DEM data DEMs have been created at a variety of scales by different agencies. Some can be downloaded free – all except the top one in this list AGENCY  SCALE  TYPICAL RESOLUTION (metres) B. Municipal  1: 5,000  1  B. Provincial  1: 20,000  25  A. Federal  1: 50,000  50 1: 250,000  200  A. Global  1: 1,000,000  500-1000  e.g City of PG BC TRIM -> www.geobase.ca CDED: Canadian Digital Elevation Data C. Global-SRTM 1: 100,000 90

How have DEMs impacted relief depiction ? Sugar-loafs and hachures – added graphically (not a software option) Contours Hypsometric Tints Shaded relief (hillshading) Tanaka illuminated contours Slope zones 3D perspectives Fly throughs True 3D

Contour lines can be interpolated from DEM heights or pre-exist from digitised maps, and are a standard layer in digital databases and online web mapping for display.

Hypsometric Tints Selection of hues, chromas from colour sequences <- legend labels

Shaded relief (hillshading) Addition of shading from an imaginary Northwest Light source http://www.gitta.info/TopoCart/en/html/ContTopo_learningObject2.html

Shaded relief (hillshading) : No longer does the practitioner require artistic ability. The user selects azimuth and zenith, 315 and 45 standard to match the NW light source. It is easily generated but may not be as good as from a skilled artist

Using the transparency option for shading and tints

JLC Geomatique – addition of shaded relief to topographic maps For BC TRIM maps, see: http://canadamapstore.com/ProductCategorySample.aspx?id=1

Tanaka relief contours – not a common software option

Tanaka Contours – Forests for the World (by applying hillshading to contours)

Slope and aspect layers (GIS analysis)

3D perspectives: Rocky Mountain trench – Castle Creek Glacier

Trails – UNBC to Peden Hill Dan Abraham, 2005

3D perspectives Perspectives are produced by GIS and visualization software. The user selects parameters such as viewing angle, vertical exaggeration and what may overlay the terrain, such as a 'draped' aerial photograph, scanned map or map layers.

Whistler – Brandywine Meadows

Whistler – Brandywine Meadows (terrain + shaded relief)

Four DEMs (North Vancouver): 1km (GTOPO30), SRTM (90m); CDED 1:250,000 (100m); CDED 1:50,000 (25m) CDED = Canadian Digital Elevation Data http://members.shaw.ca/davepatton/demcompare.html

Four DEMs (North Vancouver): 1km (GTOPO30), SRTM (90m); CDED 1:250,000 (100m); CDED 1:50,000 (25m) Pick your own map sheet in Lab 7 / assignment #2

Physical Models: Challenger map (1947-54) 25 x 25 m ~1:50,000

True 3D physical models http://www.stm-usa.com/bc.htm (40 x 74 feet 1:99,000) http://www.stm-usa.com/bc.htm