This is a collection of four scripts which help with aligning layers for HDR and mask workflow, as well as simply scaling, moving, or rotating layers.
Ortho by Path: Often the horizon on a photo is not level, or a building is not straight up. The gimp corrective rotate function works for this, but it is not that easy to use. Ortho by Path works by marking two points on the image that should be orthogonal (vertical or horizontal). The script will automagically rotate the image and will infer the direction by the angle of the path because most images require only a little straightening. An optional third point on the stroke will mark the centre of rotation. If only two points are marked, the layer will rotate about the centre.
Scale by Path: A two-point path is drawn marking two points on the reference layer as a reference length. The same two points on the active layer are marked using a second stroke (shift-click to start a new stroke in the same path). The script will scale the active layer by the ratio of the two stroke lengths.
Move by Path: A two-point path with the first point being the spot on the active layer which is to be moved, and the second being the spot on the reference layer where the first spot must align directly over.
After the move, a new path is created, ready for the next operation in the workflow, rotation.
Rotate by Path: A three-point path is created, the first being the point on the active layer that must be rotated, the second being the pivot point or centre of rotation, and the third being the reference point on the reference layer the image is to be rotated to. If Move by Path was used previously, the path is already created for you, the top point must be moved to the active layer's spot to be rotated, the right-most point must be moved to the reference point on the reference layer, and the pivot point is the same as the point we moved earlier.
Look for the menu items under "Layer/Transform/With Path..."
I hope you find these useful!