EE can be used to generate and display a digital elevation model (DEM). This feature helps the viewer better understand the topography around the model domain and can be used to create realistic fly-throughs of an area of interest.
The Three Gorges Dam in China is used as an example (this model can be downloaded from the EEMS website and loaded in the Demo version of EEMS). In order to generate a DEM in 3D, it is first necessary to have correctly formatted digital elevation data. The data should be saved as ASCII file (*.txt, *.dat, *xyz) in three columns. The first and second columns are Easting and Northing coordinates, the third column is the corresponding elevation.
Generate a DEM file
Generate DEM option can be accessed from several places as Layer Control in the 2DH View or in the 3D View or from the Tools menu as shown in Figure 1 and Figure 2.
Figure 1. Generate a DEM option from Layer Control in 2DH View.
Figure 2. Generate a DEM option from Layer Control in 3D View.
Once the option is selected, the Generate DEM form will appear as shown in Figure 3. From this form, the user click on Add File then browse to the digital elevation data file (*.xyz). Once loaded, the coordinates of the Lower-Left and Upper-Right points will be updated as well as the Cell Size and Number of Cells, the user can change the Cell Size then click on the Calculator symbol to update the Number of Cells and vice versa. The more number of cells the higher resolution of the DEM file. There are three options for DEM file output format as TB2, ArcGIS ASCII Grid, and Surfer ASCII Grid. Select one from those options then click the Generate DEM button to start generating DEM file.
Figure 3. Generate DEM form.
Once, the Generate DEM button is selected, the Export DEM form is displayed as shown in Figure 4. Enter a name in the File Name (e.g Generated DEM), select the folder directory to store the file then click Save button as shown in Figure 4. When DEM file generation has done, an informing message will be popped up as shown in Figure 5. Click OK button to exit the form.
Figure 4. Export DEM to a file.
Figure 5. DEM generated completed.
Load a DEM file in 3D View
Open the 3D View, click the Import External Layer in the Layer Control. The Open External Layer form will be displayed. Select the DEM data file from the drop-down list next to the File Name box as shown in Figure 6. Select the DEM file then click Open button. The DEM layer will be added to the Layer Control and displayed as Figure 7.
Figure 6. Import DEM file.
Figure 7. DEM displayed in 3D View.
The user can adjust vertical exaggeration to having a better view by changing the Vertical Scale Modifier in the form of 3D View Settings by RMC on the legend as shown in Figure 8. to set the DEM’s properties by RMC on this layer in the Layer Control.
Figure 8. 3D View Settings.
RMC the layer and select Properties option as shown in Figure 9, the user can edit the DEM layer.
Figure 9. DEM properties.
Figure 10. DEM properties.
Figure 10 shows DEM Layer Properties form. There are a number of options from this form as described below:
Layer Name: this allow to enter a name for the DEM layer. This name will be updated on the Layer Control and the legend as well.
Visible: turn on/off the DEM layer for view.
Shaded Relief: to represent the DEM on maps in a natural, aesthetic, and intuitive manner.
Show in Legend: to show on/off the DEM layer in the legend.
Show as Raster: to show the DEM layer as raster.
Color Ramp frame
Single Color: this option allows to display the DEM as a solid color.
Opacity: to adjust the transparency level of the DEM layer.
Min. Value, Max. Value: when the Automatic box is unchecked, the user can enter a Min and Max values.
Color Ramp: Optional selection of color ramp set for DEM from the drop-down list.
Reverse: Reverse order color ramp.
Under Range: Set color for value less than the Min value.
Over Range: Set color for value greater than the Max value.
3D View Options frame
Flip North - South: turn over the layer into a different position
Vertical Exaggeration: to adjust vertical scales.
Datum Adjustment: Enter a positive number to raise up the DEM and a negative number to lower the DEM.
Use Overlay Image
This option allows to use geo-referenced map (e.g Google satellite image) to cover the surface of the DEM. Checked on box then click Browse button to browse to the geo-referenced image as shown in Figure 11 then click Open button and result is shown in Figure 12.
DEM Info: display general information of the DEM file as DEM size, cell size, X, Y, and Z range.
The Convert Height allows to convert the height of the DEM from the current unit (e.g meter) to other units (e.g foot). When this option is selected, the DEM Height Conversion form will appear as shown in Figure 13. Click the Convert button on this form then click the OK in the Figure 10 to implement the conversion. The new color ramp range for DEM will be updated on the legend.
The Flip button allows to adjust the grid fit to the DEM.
Figure 12. Open Overlay image.
Figure 12. DEM covered with a satellite image.
Figure 13. DEM height conversion.