The Other Tools multi panel gathers functionalities which are not related to any of the previous modes:
To learn more about multi panels read this page.
Orient UVs to the 3D space
The Orient UVs to the 3D space functionality rotates every selected UV island so that the resulting UV mapping for that island matches a selected 3D axis with a selected UV axis. You can think about such a match in the following way: with given two axes matched, the texture direction on a 3D geometry along the given 3D axis will be the same as the texture direction along the given UV axis in the UV space.
Look at the images below for a visual explanation of this concept.
The first image shows an example 3D object with a texture mapped onto it before orienting UV islands to the 3D space:
As you can see, there is no any order regarding the texture direction on the planes forming the object.
The next image shows the same object after orienting UVs to the 3D space:
Note how all vertically-oriented planes of the object have now the texture mapped in the same direction (the up direction). That’s because the orienting operation was configured to match the 3D axis Z (the up axis) with the UV axis Y (the up axis in the UV space).
Note also that the objects consists of horizontally-oriented planes as well - the mapping on these planes was ordered by the operation as well but the order is not based on the texture direction along the 3D axis Z. The point is the horizontal planes are perpendicular to the 3D axis Z - that’s why it is impossible to consider texture direction along that axis on them (it doesn’t make sense from the mathematical point of view). That’s the reason why in a general case the orienting operation also needs the second pair of axes to match (read below for details).
The UI of the Orient UVs to the 3D space functionality looks as follows:
In the UI you can set two pairs of axes to match: the primary pair and the secondary pair. Every pair consists of a single 3D axis and a single UV axis. During the orienting operation, the packer first try to orient a UV island so that the resulting mapping matches the primary 3D axis with the primary UV axis. If such an attempt fails (i.e. the 3D geometry corresponding to the given UV island is perpendicular to the primary 3D axis), then the packer tires to match the secondary 3D axis with the secondary UV axis. If the second attempt also fails (the 3D geometry is perpendicular to the secondary 3D axis as well), the packer leaves the islands intact. Such a situation means the 3D geometry corresponding to the given UV island has a degenerated form.
Note that the addon prevents setting the primary 3D axis and the secondary 3D axis to the same value.
The UI also provides the Primary/Secondary Bias parameter. It’s an angle (from 0 to 90 degrees) defining to what extent the packer favors orienting using the primary axes over the secondary axes. The greater value of this parameter, the more likely the packer will use the primary axes for orienting. The default value (80 degrees) should be optimal for most scenarios. Do not change the value of this parameter unless really needed.