Example Data
The data files used in the example can be downloaded here.
Background
Canadian Digital Elevation Data (CDED) sets are freely available
from the GeoBASE site:
http://www.geobase.ca
The Canadian Digital Elevation Data (CDED) consists of an ordered array of ground elevations at regularly spaced intervals. The source digital data for CDED at scales of 1:50,000 and 1:250,000 is extracted from the hypsographic and hydrographic elements of the National Topographic Data Base (NTDB) or various scaled positional data acquired from the provinces and territories.
CDED files contain a Western and an Eastern section corresponding to half an National Topographic System (NTS) map sheet. Depending on the latitude of the CDED section, the grid spacing, based on geographic coordinates, vary in resolution from a minimum of 0.75 arc seconds to a maximum 3 arc seconds for the 1:50,000 NTS tiles, and from a minimum of 3 arc seconds to a maximum 12 arc seconds for the 1:250,000 NTS tiles respectively. Ground Elevations are recorded in metres relative to Mean Sea Level (MSL), based on the North American Datum 1983 (NAD83) horizontal reference datum.
CanMatrix - Digital Topographic Maps of Canada (NTS maps) are
also freely available from the GeoGratis web site:
http://geogratis.cgdi.gc.ca/geogratis/en/download/raster.html
The scanned NTS maps are in NAD 83 GeoTif format.
Terrain Tools will read both CDED and NTS formats. Once in Terrain the DEM data can be used for visualization, contouring, profiles, volumes etc.
Importing DEM data
Before we load the DEM we set the Projection to UTM Zone 10, NAD 83. NOTE: Both the DEM data and the NTS scanned map sheet are in NAD 83 (even though the legend in the NTS scanned map says NBAD27).
1) Choose menu Module | Setup | Projections. Set the parameters as shown in the figure below.
Figure 1: Projections Setup Dialog
2) Select menu File | Insert File, and choose dem (*.dem,*catd.ddf,*.adf) in the Files of Type dropdown and enter the name of the file (092g10_0200_demw.dem.dem).
Figure 2: Insert File Dialog
3) The Import Options dialog box shown below will appear. Enter the parameters as shown.
NOTE: The Create 3D check box will automatically create a TIN model from the elevation points. The Spacing Increment allows you to thin the incoming points. A spacing increment of 10 will accept every 10th point.
Figure 3: Import Options Dialog
NOTE: CDED's can be very large. Also they are referenced by horizontal lat/lon coordinates.
4) The Incoming Coordinate System Dialog will appear and you will be prompted to convert coordinate systems. Choose the Transform Option.
Figure 4: Transform Coordinate Dialog
Transforming the coordinates may take a few moments.
Once the DEM has been imported it can be used for surface modeling, profiles, volumes etc.
Figure 5: 3D View
We'll now add the Scanned NTS Topo image.
5) Choose menu File | Insert File, choose til (*.tif,jpg....) in the Files of Type dropdown and enter the name of the file (092g100_tif).
Figure 6: Insert File Dialog
6) Choose menu File | Insert File, choose til (*.tif,jpg....) in the Files of Type dropdown and enter the name of the file (092g100_tif).
7) When the Import Options Dialog appears choose the parameters as shown in the figure below.
Figure 7: Import Image Dialog Box
To complete this example we will overlay the NTS image in the 3D window.
8) Activate the 3D Window and choose menu Active Window (3D) Options. Turn on the Drape Plan Image option and click on the "+" beside it. Change the Drape Quality to the highest.
Figure 8: 3D Display Options
9) Press OK twice and allow the 3D Window to redraw. The
screen should appear as shown below.
Figure 9: 3D Display with Draped Topo