L3DT documentation
Large 3D terrain generator

Overlaying a land type using a mask map

The attributes map mask overlay allows you to cover an area of the attributes map with a selected land type, with the coverage controlled by a mask map (like an alpha map). The mask map may come from two sources:

  • loaded from an image file (e.g. drawn by hand, or calculated by another program), or;
  • an existing map in the project (e.g. from the mask generator).

To use this option, select the 'Operations→Attributes map→Mask overlay' menu item. This will open the attributes map mask overlay window, shown below:

The ‘attributes map mask overlay’ window
The attributes map mask overlay window


The settings in this window are described below:

Use map file as mask

Use this option to load a mask from an image file.

Selecting this option will automatically open a file browsing window with which you can select the mask image. Supported file formats include bitmap and PNG. All images are imported as 8 bit greyscale.

Use project map as mask

Use this option to select the mask from one of the maps in the current L3DT project.

Selecting this option will open the project map drop list, from which you can select the mask map. Note that this list only includes the maps in the project that are suitable for use as masks (i.e. 8-bit and 16-bit integer maps.)

Suitable mask maps can be generated using the ‘Operations→Mask maps→Generate masks’ menu item (see user guide), or by using the 'Layers→New map layer' menu item (see user guide)


The threshold slider allows you to set the greyscale level in the mask map above which the land type will be applied to the attributes map. For example, a threshold of 50% means that any points in the mask map that have a value of between 50% (medium grey) and 100% (white) will cause the selected land type to be applied to the corresponding area of the attributes map.

Climate and Land Type

You can use the climate and land type dropdown lists to select the climate and land type to be applied to the attributes map by the mask.

If you select the '« auto calc »' option in the land type drop down list, L3DT will calculate the land type that best matches each pixel of the masked area, using the same calculation as used for generating the attributes map.

Selected areas

You can limit the area of the attributes map that is modified by the overlay by using either the select area mouse tool or the 'edit->select area' menu option. You should make your selection on the attributes map, prior to opening the attributes map mask overlay window.

The overlay area is interpreted one of two ways, depending on whether you selected the use map file as mask or use project map as mask check boxes:

When using a mask map file

If the mask is loaded from an external map file, the mask is stretched to fix exactly over the selected area, and has no effect outside the selected area.

When using a project map

If the mask is an existing map in the project, the mask is stretched to cover the entire attributes map area 1), but the overlay calculation is cropped to apply only in the selected area.

When you click OK

L3DT will apply the mask to the attributes map, and re-draw the attributes map when complete.

If you are unsatisfied with the result, you can use the 'Edit->Undo' menu option to reverse the changes.

Further reading

1) All maps in the project cover the same area, as a rule
l3dt/userguide/ops/am/maskoverlay.txt · Last modified: 2017/08/31 05:01 (external edit)
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