Institutionen för geovetenskaper Geoinformatiklaboratoriet

GIS Exercise 14 October 1999

Thomas Gumbricht

DIGITAL ELAVTION MODELS AND 3D VISUALISATION

Digital Elevation Model (DEM)

In the exercise you shall use a digital elevation model (DEM) in combination with the VLF data. To fit the interpolation of the VLF data to the same area and resolution as the DEM you must add the DEM to your view before interpolating. Start ArcView with a new empty project. Under File in the project menu check that the Extension Spatial Analyst is marked. Add the DEM –the DEM is in the form of a tif. File – thus you must add it as Image Source.  

To convert the tif file to a raster image in ArcView format go to the Theme menu and Convert To Grid. Save the Grid data set in your working directory.

Look at the Theme Properties of the DEM. The DEM has a resolution of 50 meters with 501 times 501 cells covering the study area. In comparison with other data the values in Swedish DEM represent point values at nodes rather than averages over cells – thus there are 501 instead of 500 values covering the 25 km. To fit the VLF data to the DEM you must interpolate the VLF data to the same system.

Before continuing have a look at the DEM. Open the Legend Editor and classify the DEM into 25 classes, and apply one of the special DEM Color Ramps (furthest down among the defined color ramps). Legend Type must be set to Graduated Color. Return to the View, make sure the DEM is the active theme and under Surface in the menu Compute Hillshade.

Have a look at the Hillshade that you just calculated. You shall now combine the Hillshade with the DEM. Make the DEM the active theme. Again open the Legend Editor and press the Advanced button in the lower left corner. Select the Hillshade as Brightness theme and Apply. Play around with the possibilities for setting color ramps and parameters for the brightness theme until you get a satisfying image – the aim is that you should be able to see the valley systems over the study area (indicative of tectonic zones).

3 D visualization

Go to the project window and start the 3D analyst Extension under the File menu. Return to the view. Make sure the DEM is the active theme. Under Theme in the menu choose Convert Grid to TIN, accept the default values suggested for conversion. Save the TIN in your working directory. Do not add the theme to the View. Instead close the view and return to the project window. A new type of document 3D Scenes has been added to the project window – but you must use the scroll bar to see it. Click on the 3D scenes icon and then New to create a 3D scene in your project. The 3D scene consists of two windows – one viewer and one table of content. With the 3D scene active use the Add theme button to add the TIN theme that you created from the DEM. Navigate to the directory where you saved the TIN, remember to change the Data Source Type to TIN Data Source. Use the little sail ship, to rotate the 3D image.

Most of the other tools in the 3D scene are familiar. There are a few new ones, including Select Features,

, and Rotate Viewer,

.

There is almost no vertical resolution in the 3D scene that you created. To set the 3D exaggeration factor press 3D scene in the menu and then Properties. Use the Calculate button next to the Vertical Exaggeration Factor, and Apply. In the 3D scene Properties you can also change the change the sun azimuth and sun altitude of the 3D scene – try to change them to see what happens.

The next step is to add the tectonic zones to your 3D scene. Again use the Add theme button, and add the shape file with the tectonic zones (..sgu/berg/tekt10f.shp). Make the theme active and under the Theme menu choose Convert to 3D Shape File. For Z value you should choose surface (default). Save the 3D shape file in your working directory and add it to the 3D scene. In the 3D scene below the Color Ramp has been changed a little to highlight the low laying areas as lakes. You should have approximately the same 3D scene.