Pack UVs Dialog

Select an object. > Modify panel > Modifier List > Object-Space Modifiers > Unwrap UVW > Edit button (on Parameters rollout) > Tools menu > Pack UVs

Interface

(drop-down)—Sets the packing method:

Linear Packing—Uses a linear method to lay out the faces. This method is fast but not very efficient, and tends to leave a lot of unused Uv space.
Recursive Packing—Slower than the Linear method, but packs the faces more efficiently.

Spacing —Controls the amount of space between clusters.

The higher this setting, the 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.

OK—Accepts the settings, closes the dialog, and performs the packing as specified.

Cancel—Undoes any changes and closes the dialog.

Set As Default—Makes the current settings the defaults for the current session.