Straight UV

This will UV unwrap selected faces based on face islands generated using edges marked with UVs. The Follow Active Quads operator will be used on each UV island which will flatten or rectify them.

Figure 1

This will also average island scales and pack the UV islands after the unwrap. This could sometimes fail because the script uses commands that require correct poll or basically the mouse cursors needs to be inside a particular window for the command in the script to work. If this happens, just manually do them by using the Average Island Scale and Pack Islands operators respectively, they can be found in the UV editor window in the UV menu. Sometimes after doing it manually, it works in the succeeding operations. ¯_(ツ)_/¯

This operator will only work on quad faces.

It would be best if you have a UV editor window open to view the result. The operator can work in object mode but the UV map can only be viewed in edit mode.

Figure 2

Enable the UV Sync Selection in the UV editor window if you want to match your face selection in the 3D viewport to the UV map. This will make it easier to use the operator because it works on selected faces.

Figure 3

Here are the redo properties and what they do:

Limit

This has two options: UV and Sharp Edges. UV will generate the face islands based on uv marked edges as boundaries. Sharp Edges will generate the face islands based on sharp edges using an angle threshold.

Figure 4

The Sharp Edges option can freeze Blender if used on objects that has too much detail. Only use it to break up UV islands that has overlapping faces after using the UV option.

Edge Length Mode

Edge length mode used by the Follow Active Quads command used inside the script. This determines how the other faces in the UV island will be formatted based on the edges of the active face.

Figure 5

Min Edge Length

The minimum edge lengh a face has to have to be considered as the active face for the Follow Active Quads command. This avoids using lenghty thin faces which results to the other faces inheriting the shape.

Figure 6

Face Seed

Randomizes the active faces using a controlled seed number.

Figure 7

Margin

The UV island margin.

Figure 8