What is the easiest way to move object using 3 points (to have same transform for two objects)

Question

Usually when I work with photogrammetry or in other usages, I need to combine two meshes that have different position, rotation and sometime even scale.

The best way to solve this problem is by selecting 3 points that are present in both model.

• Using 1 point : have the correct location of the model in 1D

• Using 2 point : have the correct location and rotation and scale in 2D

• Using 3 point : have the correct location and rotation in 3D (scale is usually consistent and done in with two point)

Here is a GIF example of my method.

As you can see, I use an edge that I extrude in X direction, apply to rotate to my control point, and parent it to my object to have the 3rd axe of movement (locked between the two points a damp track can be used if you want make sure it stay connected to the two first point control) using object local rotation.

I don't think it's the best method, do you know if there is another way to do it faster and easier ?

Edit : I took the example with monkey as it was easy to understand, but I often need to merge transforms of more complex mesh like for example in photogrammetry. I already work with this 3 point method, it's just I think it's a long and fastidious process, and if there is already an addon, or a tool in blender that allow to make the 3D cursor rotation perpendicular to the line between point 1 and point 2, this would make things easier.

Thanks.

Answer 1

If the the meshes are identical, apart from the translations, rotations and scale, this can be done by snapping alone, I think the only bit you could improve is using a Custom Orientation?

• Set Snap to To: 'Vertex' With: 'Active', influencing translation, rotation, and scale.
• Set Pivot to 3D Cursor.
• Establish a common vertex, and ShiftS place the 3D cursor there, on the target mesh.
• Create a Transform Orientation from a common edge from that vertex, on the target mesh.
• Snap the (active) source common vertex to the target vertex...

(above)..

• Make the other end of the common edge active on the source

• RX and RZ align the common edges.

Next, the scaling step:

(below)..

• S scale the source object, snapping the common edges to scale.
• Now you can RY rotate the source around the common edge, snapping another convenient active vertex to the target:

(You could also deal with non uniform scaling, in a similar way, now, if you needed to)