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 settings in this window are described below:

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 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.)

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.

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.

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:

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.

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.

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.

• About the attributes map
• Using climates and land types
• Mask map operations
• Scripting the calculation
• Using in ZeoGraph