[048] Global Mapper - DEM Partial Elevation Correction: Terrain Paint Options

In our last session, we covered how to correct an entire DEM layer.

Today, we will learn how to modify only a specific area of your DEM data.

"Before we begin, if you missed the previous session, check it out here:"

[047] Correcting DEM Layer Elevation: Alter Elevation Values

With your DEM data open:

[img 1 : Enable Terrain Painting icon in Global Mapper toolbar]

Click the Enable Terrain Painting menu.

The Terrain Paint Options window will appear.

[img 2 : Terrain Paint Options window interface]

Terrain Paint Options Breakdown

Layer: Select the DEM layer you want to partially correct.

Selected Layer Cell Size: This shows the grid size of the currently selected DEM layer. Note that trying to modify an area smaller than this size is generally meaningless.

Operation: This defines the correction method. There are a total of 9 modes:

[img 4 : List of available Terrain Painting operations]

• Fill Gaps: If there are 'NoData' or empty values (gaps) in the elevation data, it fills them by automatically interpolating based on surrounding values.
• Smooth Terrain - Average: Averages the elevation values within the brush range to make the terrain smooth.
• Raise Terrain Height: Increases the elevation of the selected area by a specified value (only affects terrain lower than the input value).
• Lower Terrain Height: Decreases the elevation of the selected area by a specified value (only affects terrain higher than the input value).
• Set Terrain Height: Fixes the elevation of the selected area to a specific designated value.
• Slope Terrain Along Line: Changes the terrain into a slope along a line (applies the slope based on the start and end elevations of the line).
• Slope Terrain Across Line: Sets a slope in the left and right directions based on the line (useful for expressing cross-sectional slopes).
• Set to 'NoData': Removes the elevation values in the selected area.
• Revert to Original Heights: Returns the modified terrain back to the original DEM elevation values.

Brush Types

There are 6 types of brushes available:

Brush Types

From the left: Point, Line (vertex mode), Line (trace mode), Area (vertex mode), Area (trace mode), and Selected Features.

In practice, Selected Features is the most frequently used. Since most corrections are based on design plans, we usually don't change the terrain arbitrarily without a reference feature.

The remaining menus below adjust based on the Operation or Brush Type selected.

[img 5 : Adjusting Brush Size and Feathering settings]

Practical Example: Leveling a Site

Let's try one. Suppose a site is planned halfway up a mountain with a planned elevation of 200m. The site boundary should already be reflected in your design file.

1. Select the site area and run Terrain Paint.

2. Change the Operation to Set Terrain Height and choose Selected Feature as the Brush Type.

3. Set the Height value to the planned elevation of 200m. Set Feathering to about 20, then click Paint Selected Features.

[img 6 : Selecting the target area on the map with the elevation legend visible]

(Don't close the Terrain Paint window yet!)

Now, let's check if it was applied correctly.

[img 7 : Terrain view after applying the 200m height correction]

Yes, it has been applied.

Understanding Feathering

To briefly explain Feathering: our planned elevation is 200m, and we set the Feathering to 20. Feathering uses the Cell Size as its basic unit. This means the terrain is smoothly blended from the corrected site boundary outwards for a range of 20 cells. It essentially creates a slope over those 20 cells to match the original terrain height at the 21st cell.

Shall we look at a cross-section?

[img 8 : Drawing a line across the site to generate a Path Profile]

Draw a straight line through the target site, then right-click and select Analysis/Measurement -> PATH PROFILE - Generate Path Profile Along Line(s)....

[img 9 : Path Profile showing the leveled 200m area and the feathering slopes]

The cell size of the DEM we worked on was 5x5m. The slope looks to be roughly 20 cells wide, which is correct.

Many of you might think, "Oh! I should use this to create road embankments!" However, the options aren't quite that precise. When installing a road on a hillside, you need an upward slope for the higher side and a downward slope for the lower side. With this tool, if you set a slope value, it creates a high slope regardless of whether the surrounding terrain is higher or lower than the road.

Feel free to experiment with the other options yourself.

That's all for today!

"In the next session, we'll dive deeper into more advanced features. Stay tuned!"

[053] Comparing Terrain Changes: Path Profile

[049] Adding Points, Lines, and Polygons using CSV Files