How to display

Digital Elevation Models

A (digital) representation of relief over space is known as a digital elevation model (DEM). By relating any map with the corresponding terrain surface in a 3D model, you can discover and understand relations between spatial data sets. For example, by draping a land use map over the height values of a 3D model, you can see where your areas of interest are located: on slopes, on flat areas, in the lower areas, in the mountains, etc.

Although Display 3D was originally developed to model relief, it can of course also be used to model the continuous variation of any other value map as a surface (e.g. concentration values, land values).

To obtain a Digital Elevation model, you can digitize contour lines and assign height values to the segments in the segment editor. Then use the Contour Interpolation operation. The output is a DEM, also called a height map. For more information, see How to calculate a Digital Elevation Model.

1. Using the Shadow filter:

An easy method to get a general impression of your relief is to apply the Shadow filter on your DEM with the Filter operation. When you display the result in a map window, you can already see the relief coming out of the map.

To start the Filter operation:

The Filtering dialog box appears.

In the Filtering dialog box:

When you display the output map in a map window, choose Representation Gray; additionally you can add the segment map with the contour lines and display these in one color (e.g. light brown).

When the output map uses 4 or 8 bytes per pixel, you may first calculate a histogram of the filtered map with the Histogram operation to enhance the display.

2. Creating a three dimensional view:

Another method is to create a 3D view out of your DEM with the Display 3D operation; you create a georeference3D in the georeference 3D editor.

To start the Display 3D operation:

The Display 3D dialog box appears.

In the Display 3D dialog box:

The Display Options - 3D Grid box appears.

   

(When you already have a georeference 3D, you can open it by double-clicking it in the Catalog, or in the Catalog, click the georeference 3D with the right mouse button, and choose Open from the context-sensitive menu. The Display Options - 3D Grid box appears.)

In the Display Options - 3D Grid dialog box, you can specify how the 3D view should be displayed:

The DEM is displayed in three dimensions in a map window.

To modify the 3D view (i.e. the georeference 3D):

The Georeference 3D editor is opened.

The Georeference 3D editor mainly consists of one large Georeference 3D dialog box in which you can specify parameters (altitude, rotation, distance, vertical exaggeration, etc.) to define the perspective of the observer in relation to the 3D model. Some examples of the effects of changing parameters in the dialog box are presented in Georeference 3D editor : functionality.

When finished editing the 3D view, you can exit the editor and return to the map window. If you like, you can add any other vector map or annotation to this map window. You can save the 3D view in the map window as a map view.

3. Combination of a 3D drape and a Shadow map:

A simple and nice 3D view of a Digital Elevation Model can be obtained by using the output map of the DEM filtered with the Shadow filter as a raster drape over the height values and by overlaying the contour segments on the 3D view.

Start the Display 3D operation and create a suitable georeference 3D with the Georeference 3D editor (see above).

In the Display Options - 3D Grid dialog box:

The 3D view appears in a map window.

Drag the segment map with the contour lines from the Catalog to the map window. The Display Options - Segment Map dialog box appears.

In the Display Options - Segment Map dialog box:

The Shadow map is displayed in three dimensions in the map window and the segment map with the contours is overlaid on the 3D view.

Then, to save your 3D view (incl. contour lines),

4. Resampling a map to a georef 3D:

Lastly, to permanently display a raster map in as a 3D view, use the Apply 3D operation. This operation resamples a raster map according to a georeference 3D. When you create a map list of raster maps that are the outcome of an Apply 3D operation (for instance depicting the same area in three dimensions but from different angles), and display this map list as a slide show, you can obtain a kind of rotating DEM with raster drape.

See also: