005] Global Mapper - Viewshed Analysis

Following our previous session, today we will dive into Viewshed Analysis in Global Mapper.

Viewshed Analysis is primarily used to identify changes in visible areas caused by a specific project or development. It is an analytical process where you select key viewpoints and look toward the project site to compare the current status with the planned state to see how much the visibility changes. (In practice, many people often perform only the current status viewshed analysis.)

In the past, when performing viewshed analysis including buildings in software like Q-GIS or Arc-View, you had to convert the buildings into a DEM (Digital Elevation Model) and overlay them on the terrain. However, Global Mapper has a significant advantage: it allows you to analyze building vector data directly without converting it to a DEM. This feature has been available for over 10 years in Global Mapper, and while other programs might support it now, it has long been a standout function here.

Let's get started.

Since modifying building attribute values is a separate task, today we will focus solely on the terrain for this demonstration.

Step 1: Load Your Workspace

First, load the Workspace we created in the last session.

If you have loaded the work from the previous session, your screen should look something like the state shown below.

Step 2: Accessing the Viewshed Tool

From the icon toolbar, select the Create Viewshed icon (it looks like a lighthouse beam or a signal coming from a mountain top).

Upon clicking, a tip message will appear with some instructions and a prompt to pick the starting point for the analysis.

Check "Don't Show This Again" and click OK.

Step 3: Selecting the Observation Point

Your mouse cursor should have changed. Click on the map at the location where you want to place the "transmitter" (the observer's position).

Step 4: Viewshed Setup and Parameters

Once you click, the Viewshed Setup window will appear. Here is a breakdown of the key settings:

• Layer Name: You can enter a name for the new layer that will be generated.
• Transmitter Elevation: Think of this as the observer's eye level. By default, it might be set to 1.6 meters above the ground at the clicked point.
• View Angle: This sets the starting azimuth and the range of the analysis around the observer.
  • Start Angle: The azimuth where the analysis begins.
  • Swept Angle: The total range of the arc. (For example, a Start Angle of 290 and a Swept Angle of 60 means the analysis covers from 290 degrees to 350 degrees clockwise).
• Earth Curvature: Check this if you want to ignore the earth's curvature. For short distances, it doesn't matter much, but for long-range analysis, it is significant.
• Display Color: Choose the color for the visible areas.
• View Radius: Defines how far from the observer the analysis should reach.
• Sample Spacing: Sets the cell size for the analysis. Smaller values provide more accuracy but take longer to process.
• Use Vector Features with Heights: Enabling this allows vector elements (like buildings) with height attributes to be included as obstructions in the analysis.

Once you have configured these settings, click OK.

Step 5: Reviewing the Results

The results are now displayed on your map!

If you wish to modify an existing viewshed analysis, simply right-click the corresponding layer in the Control Center and select "Edit Viewshed Parameters and Recalculate." Adjust the settings in the dialog box and click OK to refresh the analysis.

Advanced Capabilities

Since this is a brief overview, I've kept it simple. While we used a mouse click to set a point today, you can also:

• Register specific viewpoints as a layer and analyze them.
• Select dozens of points at once for batch processing.
• Overlap visible areas to determine "Visibility Frequency."
• Import building data, assign height attributes, and include them in the simulation.

While it might not compare to high-end 3D specialized software, for general GIS workflows, Global Mapper is incredibly convenient for "setting the stage" and getting reliable results quickly.

I assume those who find their way here searching for Global Mapper already handle at least one GIS tool for their professional work. I'm presenting this as a high-level overview so you can compare it with the tools you currently use.

That’s all for today!