Grasshopper

generative modeling for Rhino

# normal vector flipping with Circle CNR

I'm trying to make a circle that travels along the circumference of another circle.  I also used Point on Curve to place a point on the moving circle.  When I use Circle CNR, the moving circle changes orientation periodically

I've attached a file to illustrate what I'm talking about.

I used Circle CNR to make the moving circle.  The center point is a point on the stationary circle and the normal vector is a vector from the center of the stationary circle to the center of the moving circle.

The orientation of the moving circle seems to flip every pi/2 radians--at pi/4, 3pi/4, etc.  I can tell because the point on my moving circle jumps from one side of the circle to the other.  I think this has something to do with the way the Circle CNR component works.  If I start with the same vector, find two vectors normal to it, use them to define a plane, and use that plane to define the moving circle, everything works out fine.

Can anyone explain to me why this happens?  Is there a way to solve my problem that's faster than making a new plane or adding extra components to reverse the vector half of the time? (I'm new to Grasshopper.)

Thanks!  I'd appreciate any ideas.

Tags: circle, cnr, normal, vector

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By only using a single direction and a point to define a plane Grasshopper is presented with an infinite possible number of solutions for the other axes. Therefore your robust method of using more constraints to define the plane prevents Grasshopper from any spurious choices.

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