Select an object. > Modify panel > Modifier List > Object-Space Modifiers > Unwrap UVW > Edit button (on Parameters rollout) > Mapping menu > Flatten Mapping
The Flatten Mapping method of procedural mapping applies planar maps to groups of contiguous faces that fall within a specified angle threshold. It prevents overlap of mapping clusters, but can still cause texture distortion. The Flatten Mapping dialog lets you control how clusters are defined and mapped.
Face Angle Threshold—The angle used to determine the clusters to be mapped.
As the Flatten Map gathers faces to be mapped, it uses this parameter to determine which faces get put in a cluster. This is the maximum angle that can exist between faces in a cluster.
The higher this number, the larger the clusters will be, with consequently greater distortion introduced as a result of texture faces' proportions deviating from their geometry-equivalent faces.
Spacing —Controls the amount of space between clusters.
The higher this setting, the larger the gap that appears between clusters.
Normalize Clusters— Controls whether the final layout will be scaled down to 1.0 unit to fit within the standard editor mapping area. If this is turned off, the final size of the clusters will be in object space, and they'll probably be much larger than the editor mapping area. For best results, leave this turned on.
Rotate Clusters—Controls whether clusters are rotated to minimize the size of their bounding box. For instance, the bounding box of a rectangle rotated 45 degrees occupies more area than one rotated 90 degrees.
Fill Holes—When turned on, smaller clusters will be placed in empty spaces within larger clusters to take the most advantage of the available mapping space.
By Material IDs—When on, ensures that no cluster contains more than one material ID after flattening.
OK—Accepts the settings, closes the dialog, and performs the mapping as specified.
Cancel—Undoes any changes and closes the dialog.
Set As Default—Makes the current settings the defaults for the current session.