Orientonsrf

I am having a problem learning how to orient 1 surface into a curved surface
and then control rotation and placement in the curved surface face.

The Help file has the details.
http://docs.mcneel.com/rhino/5/help/en-us/commands/orientonsrf.htm

Most new users miss that the normal direction of the current viewport becomes the “toothpick” when orienting the object to be moved.
This “toothpick” is aligned with the target surface normal.

Not certain what you mean by toothpick?

In the User’s Guide “Penguin” tutorial (on Learn page), this command is covered when building and placing the eyes.

find the centroid of the area of both. Make sure otho is on and draw a line from the centroid through the bottom surface of the small partial sphere and the upper surface of the large upper sphere. Intersect the lines with each creating a point. Orient one surface to the other using the points as a reference.

What is special about the centroid?

Hello - if I understand what you’re after, you’d be best starting with a CPlane that corresponds to the back plane of the smaller surface - either a custom CPlane (make a `PlanarSrf` from the edge curve and `CPlane>Object`) or reorient the object onto one of the standard CPlane. `OrientOnSrf` uses the current CPlane Z axis as a basis for the direction - this is mapped to the surface normal on the target surface.

-Pascal

the centroid of those objects are located in the center of the area; the area is circular, thus the centroid is the center of the circle as well. Assuming you wish to line one up to the other on their centers, this action assures that will happen.

On the other hand the user is asking about the center of the edge - that edge is a circle and its center is not on the surface at all.

-Pascal