Combining a hillshaded DEM with a scanned map

Complexity: Intermediate Data Requirement: Use your own data

Creating a hillshaded topographic map is an example of merging two types of raster data. You could also combine a hillshaded DEM with other raster data, such as satellite imagery or aerial photography. Combining the hillshaded DEM with a scanned map or any 2D image helps you to visualize topography.

In this workflow, there are two sources of data: several tiled DEMs that join along the edges and several scanned map sheets. You will be using mosaic datasets to manage and combine the raster data sources using the following workflow:

1. Create a mosaic dataset to manage the DEM datasets.
2. Create a mosaic dataset to manage the scanned maps.
3. Create a third mosaic dataset to combine the two. (This is not necessary, but it makes the management simpler since the data is maintained individually.)
4. Add the scanned map mosaic dataset to the third mosaic dataset.
5. Apply the necessary functions to the third mosaic dataset to insert and combine the two data sources.

Create your mosaic datasets

In this workflow, you will create three mosaic datasets. Although it is possible to do this with fewer, managing your source mosaic datasets independently can have some advantages; for example, they can more easily be used as input for other mosaic datasets.

Steps:

1. Create a mosaic dataset, named DEM, to contain all your elevation data.
   1. Add your data and build the service overviews.
2. Create a mosaic dataset, named TOPO, to contain your scanned maps.
   1. Add your data and build the service overviews.
3. Create a mosaic dataset named HillShadeTopo.
4. Use the Add Rasters To Mosaic Dataset tool to add the TOPO mosaic dataset to the HillShadeTopo mosaic dataset.
   1. Enter HillShadeTopo as the Mosaic Dataset.
   2. Click the Raster Type drop-down arrow and click Raster Dataset.
   3. The Input value should be Dataset.
   4. Click the Input browse button and navigate to the TOPO mosaic dataset.
   5. Click OK to run the tool.

Add the functions

In these next steps, you will add the functions to the HillShadeTopo mosaic dataset to average the TOPO and a hillshaded DEM together: (TOPO + hillshade DEM) / 2.

Add the Arithmetic function: Plus

Steps:

1. Right-click HillShadeTopo in the Catalog window, and click Properties.
2. Click the Functions tab.
3. Right-click Mosaic Function and click Insert > Arithmetic Function.

   

4. Click the Input Raster 2 browse button, navigate to the DEM mosaic dataset, then click Add.

   By default, this operation is Plus.

5. Click OK to close the Raster Function Properties dialog box.

The function to add the pixel values of the TOPO and DEM mosaic datasets is inserted. The Functions tab now displays the Arithmetic function in the function chain and the DEM mosaic dataset has been added. You need to add the Hillshade function to the DEM to have a hillshaded scanned map output.

Add the Hillshade function

Steps:

1. Right-click DEM and click Insert > Hillshade Function.

   

2. Optionally, edit the azimuth, altitude, or z-value parameters.
3. Click OK to close the Raster Function Properties dialog box.

   

The Hillshade function is inserted above the DEM. The outputs from both the Hillshade function and the Mosaic function (which is your source TOPO) are added together. However, the TOPO mosaic dataset has three bands and the Hillshade function only outputs a one-band grayscale image. You need to insert the Extract Band function to specify that the Arithmetic function should use the single hillshaded band as input, which will be added to each of the three bands. Therefore, you'll be adding together data with the same number of bands.

Add Extract Band function

Steps:

1. Right-click the Hillshade Function and click Insert > Extract Band Function.
2. Type 1 1 1 (a space delimited list) in the Band IDs text box.
3. Click OK to close the Raster Function Properties dialog box.

   

Your DEM is hillshaded and expanded to three bands. The function to add the TOPO and hillshaded DEM is inserted in the function chain; now you can add the function to divide their sum by 2.

Add the Arithmetic function: Divide

Steps:

1. Right-click Arithmetic Function and click Insert > Arithmetic Function.
2. Click the Operation drop-down arrow and click Divide.
3. Click the Raster drop-down arrow and click Raster 2.
4. Type 2 in the Constant text box.
5. Click OK to close the Raster Function Properties dialog box.

   All the required functions are added to the function chain.

6. Click OK to close the Mosaic Dataset Properties dialog box.

View the hillshaded scanned map. You may have to refresh your view by zooming in or out.