Normal of a plane between two parented lines, responsive as angle changes

[David Alex]

Hi!
I noticed you’re using 2 null objects to define the points, so I tried it out using a shape layer as the arrow.
I made the arrow 3D and used this expression in its Position:
(thisComp.layer("1").position+thisComp.layer("2").position)/2

This places it directly in between the two.
Two rotate it in the right direction, I used this in the Orientation:
lookAt(thisComp.layer("1").position,thisComp.layer("2").position);

It won’t be completely right, but you can use the X,Y and Z rotation properties to offset and get it pointing the correct way. It also depends on how you drew the shape and which direction it was facing originally.
Hope this helps 😀

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[Darby Edelen]

You can cross multiply the two vectors to find the normal. Something like this given the 3 points that make up the vectors:


a = effect("A")("Layer");
b = effect("B")("Layer");
c = effect("C")("Layer");
v1 = a.toWorld(a.anchorPoint) - b.toWorld(b.anchorPoint);
v2 = a.toWorld(a.anchorPoint) - c.toWorld(c.anchorPoint);
lookAt(toWorld(anchorPoint), fromWorld(cross(v1, v2)));

A, B and C are Nulls in my example and this is applied to the Orientation property of another Null representing the normal. If you want the Null to always be centered between the vectors you could also use something like this on the position property:


a = effect("A")("Layer");
b = effect("B")("Layer");
c = effect("C")("Layer");
(a.toWorld(a.anchorPoint) + b.toWorld(b.anchorPoint) + c.toWorld(c.anchorPoint)) / 3;

All of the returned vectors are in world space, so if you want the Null to be parented you’d have to modify these to be in the layer space of the parent.

Darby Edelen