[017] How to Create BBOX and Point Clouds from DEM Data in Global Mapper

Generate precise vector coverage areas and convert terrain grids into individual point cloud features for detailed spatial analysis.

This tutorial provides an in-depth look at Global Mapper's layer management system, specifically focusing on Elevation Layer tools. You will learn how to differentiate between layer types in the Control Center, generate rectangular bounding boxes and polygonal coverage areas, and extract point cloud data from Digital Elevation Models (DEM).

In the last post, I shared a script related to Python, but there were some layer-related functions I hadn't mentioned yet. While we're on the topic, let's explore some frequently used features.

Global Mapper categorizes layer types into five main groups: Elevation (Terrain), Image (Raster), Point, Line, and Area (Polygon). The sub-items visible in the Layer menu change depending on the type of layer selected.

There are additional layer types, but most users probably won't need to work with them in depth

Let's start with the Elevation Layer.

One important thing to keep in mind is that Elevation Layers can be visualized as slope or aspect maps simply by changing the Shader settings.

Global Mapper toolbar showing the Shader drop-down menu with options like Atlas, Slope, and Magma Shaders
img 1 : Global Mapper toolbar showing the Shader drop-down menu

Therefore, the functions we are about to discuss can be used consistently even if the shader is changed. You can download and open the sample .gmp file below to follow along.

Attachment: Layer_Management.zip (Verified and safe file for Global Mapper.)

Looking at the layers registered in the Control Center, you'll notice that the icon to the left of the layer name changes based on the elements the layer contains (Terrain, Raster, Point, Line, or Area).

Control Center window showing different icons for Elevation, Image, Point, Line, and Area layers
img 2 : Control Center window showing different layer icons

If you select a layer and right-click, a context menu appears. At the very bottom, you will see the Layer item. The sub-items under this menu vary depending on the layer type.

Right-click context menu in Control Center highlighting the Layer sub-menu at the bottom
img 3 : Right-click context menu in Control Center

Since we are only dealing with Elevation Layers today, let's look at the context menu specific to them.

List of sub-menu items under the Elevation Layer context menu
img 4 : Elevation Layer sub-menu items

Elevation Layer Menu Functions

  1. Create Workspace File from Selected Layer(s)...: Saves the selected layer as a Workspace file (.gmw).
  2. EXPORT - Export Layer(s) to New File...: Exports the selected layer to a new file format.
  3. MAP CATALOG - Add Selected Layer(s) to Map Catalog...: Adds the layer to a Map Catalog (useful for massive, national-scale datasets).
  4. BBOX/COVERAGES - Create Layer Coverage Box/Polygon Area Features: Generates a bounding box that encompasses all elements in the layer.
  5. Create Point Cloud from Elevation Layer: Converts elevation data into a Point Cloud.
  6. Create Area Features from Equal Values...: Creates polygon features based on equal elevation ranges or values.
  7. Vectorize Raster: Converts data into vectors (lines or polygons) based on threshold values.
  8. Create Mesh Features from Terrain...: Generates mesh features based on terrain data (a preliminary step for creating TIN models).
  9. Find Extreme (Min/Max) Elevation Values...: Searches for the minimum and maximum elevation values within the layer.
  10. Link External Metadata File: Connects the layer with external metadata (XML, TXT, etc.).
  11. Save List of Layers to Text File...: Saves the current project's layer list as a text file.
  12. Set Background Color for Layer in Control Center: Sets a custom background color for the layer entry in the Control Center.

Create Bounding Boxes and Coverage Areas

Items 1, 2, 3, 10, 11, and 12 are fairly self-explanatory, so let's explore the remaining functions. BBOX/COVERAGES is a common feature used across all layer types, not just Elevation. It creates a rectangular or polygonal border that contains every element in the selected layer.

Select Layers dialog box where the user selects which layer to generate a BBOX for
img 5 : Select Layers dialog for BBOX generation

When you select BBOX, a window appears asking you to select the layers. Select "Elevation" and click OK. Then, it asks whether you want a rectangular bounding area or a polygonal coverage area.

A terrain map showing a newly created rectangular red border around the elevation data
img 6 : Rectangular Bounding Box created around terrain

Choosing "Yes" creates the smallest possible rectangle containing all elements. "No" creates a polygon that fits the actual shape of the data more closely. In the example, a new layer called Elevation (Bounds) is created.

Selecting the Point layer in the Select Layers dialog to create a polygonal coverage
img 7 : Selecting the Point layer for polygonal coverage

Next, let's try creating a polygon around a Point layer using the "No" (Polygonal) option. A Concave Hull Options window will appear, allowing you to set the "Smoothing" factor. Higher smoothing values simplify irregular boundaries

Concave Hull Options dialog box with a smoothing factor slider set to 100
img 8 : Concave Hull Options smoothing settings
Map showing a black polygonal line connecting six points over the elevation layer
img 9 : Polygonal line connecting selected points

Create Point Clouds from DEM Data

Now, let's look at Create Point Cloud from Elevation Layer. This function converts DEM (Digital Elevation Model) data into individual points, each containing an elevation value.

Export Bounds dialog box for determining the area where points will be generated
img 10 : Export Bounds dialog for Point Cloud generation

Personally, I wish there were a function to adjust the density of the generated points, but that option isn't available here. Once you click OK, an Elevation Points layer is created. In my test, it generated 44,290 features.

Zoomed-in view of the point cloud showing individual points
img 11 : Individual points within the point cloud

If you turn off the DEM layer and zoom in, you can see the individual points. By using the Feature Info Tool (Alt+P) and clicking on a point, you can inspect its attribute information, including its precise elevation.

Feature Information window showing the elevation value of 98.86m for a specific point
img 12 : Feature Information showing point elevation data

That's all for today...

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