001] Global Mapper - Creating DEMs

from http://blog.naver.com/cubizen/223618501185

This is our first session on Global Mapper.

Among the various outputs created using GIS software, we will focus on the following, which are essential for producing landscape-related reports:

• Creating a DEM

• Using Online Maps

• Analysis: Contour, Slope, and Aspect

• Path Profile (Terrain Section)

• Viewshed Analysis

And regarding saving images in Global Mapper:

• Map Layout Editor

As I experienced with CityEngine, the most important thing is simply to start. The framework takes shape as posts accumulate. Therefore, I won’t dive into every tiny detail right away; instead, I’ll provide more in-depth, supplementary explanations as we progress.

First, you’ll need to download the trial version.

On the official website, you will find the "Start Free Trial" menu.

Please note that free email accounts (like Naver or Gmail) might not be accepted; you typically need an email address affiliated with a company or an educational institution.

Once your email is confirmed, download and install the software, then proceed with the steps below.

I encourage you to compare this workflow with other software you’ve used. This efficiency is the "highlight" of Global Mapper.

Let’s begin creating a DEM.

1. Importing the Digital Topographic Map

One of Global Mapper's greatest strengths is its ability to import a vast array of file formats.

Go to File > Open Data File(s)... (Ctrl+O).

I will import a Continuous Digital Map in .shp format downloaded from the National Territorial Information Platform.

Usually, these maps are downloaded as a single ZIP file. Global Mapper is smart enough to load the data directly from the ZIP file without needing to extract it first.

The imported data consists of contour lines and spot heights (elevation points).

In the Control Center, the currently active data is managed as layers.

2. Checking the Elevation Attributes for Each Layer

To create a DEM, you must identify which attribute contains the height data in your digital map.

Select the pencil-shaped Digitizer Tool from the top toolbar and double-click on one of the contour lines.

A Modify Feature Info window will appear.

As seen in the attributes, the value under "CONT" represents the elevation.

Once you've confirmed that "CONT" holds the height data, you can close the window.

Now, right-click on the specific layer in the Control Center and select Options....

The options window will open.

Navigate to the Elevations tab. In the "Get Elevations From Attribute Value" dropdown list, select CONT and click Apply.

This tells Global Mapper to recognize the "CONT" attribute as the actual elevation value.

3. Generating the DEM Grid

Right-click on the selected layer again and navigate to Analysis > Grid (Create Elevation Grid from 3D Vector/Lidar Data...).

Select the layer(s) you wish to use for the DEM and click OK.

The Grid Creation Options window will appear.

Set the Grid Options tab as follows:

The setting depends on the size of the site, but for an area within a 1km radius, I typically set the Grid Spacing to 5 meters.

Make sure to check the options as shown in the image (e.g., Flatten 3D Area Features, Ignore Zero Elevations, and Fill Entire Bounding Box...).

Next, move to the Grid Bounds tab.

Here, you can define the area for DEM generation.

• All Loaded Data: Use this to generate a DEM for the entire extent of the loaded layers.

• Draw a Box...: Allows you to manually click and drag to select a specific rectangular area.

• You can also define the bounds using specific coordinates or by using a custom polygon area.

When you click "Draw a Box...", the following window appears:

Click and drag your mouse to define the desired area and click OK. The selected bounds will then be reflected in the main menu.

Now, click OK to proceed.

The DEM has been successfully created.

Let’s verify the result.

Click the cube icon labeled "3D" in the top toolbar.

A rotatable 3D Viewer window will appear.

The process is complete.

It might look complicated because of the mix of text and images, but the core process is very simple:

Import the file > Assign the elevation attribute in the layer options > Run the Grid command. That’s it!

I’ve only touched on the basic options for DEM generation today. I will provide more detailed explanations of the advanced features as they become necessary in future posts.

I spent a lot of time contemplating how to start this Global Mapper series, and I realized that worrying doesn't get things done. So, I just dove right in.

That’s all for today!