In the Preview tab, you can see the 2D height map, that you have generated, to better understand how the terrain is being deformed.

Black represents no deformation, with the brightest, white areas being the full deformation and, therefore, the highest gradients, controlled by the Gain value in the Operator tab.

The Preview tab in tfNoise.

Source

There are four types of Source available for every Generator operator: Altitude, which is set as default, Slope, Fields Mask and Shader Mask.

Filter operators also have the Difference Map option.

In addition, there are some operator specific modes, for example, the Hydraulic Erosion filter has Erode Map and Deposit Map options.

In this image, there are four Source types for the same terrain. From the left, Altitude, Slope, Fields Mask and Shader Mask, respectively.

Open Monitor

Opens the source preview in the Grid Monitor.

Note: The Grid Monitor can also be opened via a command in the TerraformFX menu.

This is a dockable, floating window, which can display any operator preview source of your choice.

This enables you to view the 2D source preview in real time, even when making adjustments to operator settings and parameters.

Grid Monitor floating window, giving a preview of the Altitude Source in the Grid Monitor and the Fields Mask in the Preview tab.