Viewing Canadian Digital Elevation Data (CDED)

The following procedure outlines the steps necessary for viewing Canadian Digital Elevation Data (CDED) using ArcView Spatial Analyst and 3D Analyst. This particular digital elevation model (DEM) is based on the National Topographic Database (NTDB) at scales of 1:50,000 and 1:250,000 and is available from Natural Resources Canada (NRCan) through the university DLI agreement. These data may be used for teaching and research purposes only. See the fact sheet for further details.

Steps outlining the process of ordering and receiving NRCan data can be found in the staff procedures' manual.

File Format

The CDED data were produced using the Australian National University Digital Elevation Models software. The result is a file with similar properties to the United States Geological Survey digital elevation models. Before importing the CDED file you must define the file as ".dem".

• Run Windows Explorer.

• Navigate to the directory holding the CDED data file. The directory illustrated below holds two DEM files named "030m03_0100_deme" and "030m03_0100_demw". Notice the file type is simply "file".

• To change the file type, right click on a file and add ".dem" at the end of the file name. The new file names will be "030m03_0100_deme.dem" and "030m03_0100_demw.dem". Notice that the file type has now become "DEM".

You are now ready to import the digital elevation model into ArcView. The steps for this procedure are outlined below. The same procedure is used for importing USGS digital elevation models as well.

Creating a GRID file

• Run ArcView 3.2.

• When prompted, create a new session with a new view but DO NOT add data to your view just yet.

• Choose File>Extensions and turn on 3D Analyst as well as Spatial Analyst. Be sure that these are the only extensions running for this session. Click OK.

• Choose File>Import Data Source. Select USGS DEM as the import file type. Click OK.

• Navigate to the directory holding the DEM file. Click on the file and click OK.

• You are prompted to name the output GRID file. Navigate to the same directory you have the DEM stored in and give the grid a name. Click Open.

• When the DEM has been imported you will be asked "Add grid as theme to the View?". Click YES.

• Double click on the theme in the legend to access the editor. From the Colour Ramps dropdown list, scroll down and select "Terrain Elevation #1". Click "Apply".

• Close the Legend Editor by clicking the "x" in the upper right corner of the dialogue box.

• Turn the GRID them on by clicking in the box beside the theme name.

• Select File>Save project as to create a project file of your work so far. Navigate to the directory where your data is saved and give the project an appropriate name. Click OK.

The default coordinates for the CDED data are decimal seconds. You must use an Avenue script (demshft.ave) available at http://arcscripts.esri.com/details.asp?dbid=10711 to convert the data to decimal degrees. Until you work through the procedure outlined HERE you will not be able to overlay other datasets.

Next, you may want to view the data in 3-dimensions using ArcView's 3D Analyst. The next section outlines the steps involved in this procedure.

Viewing the DEM in 3D

• With the GRID them active, select Edit>Copy themes.

• Go to the project window. Scroll down and click on 3D Scenes.

• Click on "New". A new 3D scene appears. To insert the GRID file, select Edit>Paste.

• Select Theme>3D properties... The 3D theme properties dialogue box appears.

• In the first section "Assign base heights by" click in the radial select button beside Surface.

• Check the box beside "Show shading for features" at the bottom of the dialogue box.

• To apply changes and exit, click OK. Your view now appears in 3-dimensions.

• To zoom in and out, click on the Navigate button , then RIGHT click in the scene window and drag the window towards you and away from you.

• To rotate and pivot the scene use the Navigate tool with the LEFT-click mouse option. Experiment with these different options to obtain various views.

For further information about using 3D Analyst, Spatial Analyst or ArcView consult the user manuals or on-line Help files.

This page is: http:// jeeves.brocku.ca /maplibrary/procedures/CDEDinAV.htm Last updated:  Friday, 15-Nov-2002 14:47:26 EST Any comments? info@www.brocku.ca  Brock University © 1999 Disclaimer