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While it doesn't happen often, there are rare cases where you need to correct the elevation of DEM (Digital Elevation Model) data. This technique is especially useful when flat terrain appears visually weak and you want to emphasize elevation differences in maps or 3D terrain models.

In Global Mapper, there are methods to correct DEM data by either adjusting the entire layer or correcting only a specific area.

In this tutorial, we will adjust elevation values across the entire DEM layer using Global Mapper's built-in elevation correction tools.

First, load the DEM data. I will skip the process of creating a DEM as I have already introduced it in previous lectures.

Now, select the DEM layer in the Control Center.

Select 'Options'. (You can also simply double-click the layer).

The Layer Options window will appear.

How the DEM Elevation Formula Works in Global Mapper

The most important part is the formula shown in the red box. The correction is applied according to this equation:

new_elev = (scale Factor * orig_elev^Power) + offset

(The formula follows the standard order of mathematical operations.)

If you want to double the entire DEM elevation value, enter '2' in the Scale Factor and click apply. A location that was 1m high will become 2m, and a location that was 10m high will become 20m.

If you want to raise the entire DEM by 5m, enter '5' in the Offset and click apply. A 1m elevation will become 6m, and a 10m elevation will become 15m.

If you want to raise the entire DEM exponentially, enter '2' in Power and apply it. A 1m elevation remains 1m, but a 10m elevation becomes 100m.

What if you want to double the total height and then increase it by 10m? You would enter '2' for the Scale Factor and '10' for the Offset. An area that was 1m will become 12m, and a 10m area will become 30m.

Once you understand the formula structure, adjusting DEM elevations becomes straightforward. Try entering values and check if the results come out as expected. You can verify this by displaying the elevation legend.

In atlases, we sometimes see 3D images where the contours of an entire country are applied. If you use the actual elevation as is, it often looks flat. Therefore, the elevation is corrected overall so that mountain ranges are expressed more prominently.

This workflow is commonly used for terrain exaggeration, elevation normalization, and DEM visualization enhancement.

Using Valid Elevation Range and Clamp Options

Next, let's look at the Valid Elevation Range.

• Maximum Valid: The highest elevation to be permitted.
• Minimum Valid Elevation: The lowest elevation to be permitted.

The current elevation has a maximum of 545 and a minimum of 120. Let's adjust this.

Elevation areas exceeding the maximum will be deleted. Strictly speaking, they are hidden. Don't click 'OK' yet; just click 'Apply' to see how it changes.

First, let's look at the current status.

Now, if we set the maximum to 400 and click apply:

Areas above 400 meters are now hidden from the DEM display.

You can leave these empty areas as they are, or you can fill them with a specific value by entering a number in 'Replace Invalid With'.

If you enter 200 and click Apply, the hidden areas will be replaced with an elevation value of 200 meters.

The 'Clamp Out of Bound Values to Valid Range' option applies the maximum or minimum value to parts that exceed those ranges.

If you set the maximum to 400 and the minimum to 200, and then apply 'Clamp Out of Bound Values to Valid Range':

The elevation legend is also updated automatically to match the adjusted elevation range.

How to Restore the Original DEM Elevation Range

To return to the original terrain:

Just click 'Restore Default Elevation Range'. You can return to the initial DEM at any time, so feel free to experiment with the correction values.

I didn't show the elevation legend at first, but to verify how the elevation range actually changes, make sure to display the legend while working.

That's all for today!