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Normal Direction on a Square


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I have a square consisting of several points on each side. I want the Normals to face outwards on each point. I used the expression $BBX-$BBZ in a point sop and got two of the sides doing exactly what I want, But I need it for the other two sides.

I have attached my scene file. Any help would be greatly appreciated. 



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We know we can get the type of normals you are looking for from a Facet following a box. But you only want a single square. So you can attribute transfer the normals from the box to the square after deleting all those extra box vertices.



Edited by Atom
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Hi Michael, the code you shared gives a vector which points inwards to the origin at every point.

Here's my point wrangle code that gives normals at any point on the surface of a unit box. Given all the conditionals, I assume there is probably a much more succinct solution.


vector onSurface1;
vector onSurface2;

if (@P.z == 0.5 || @P.z == -0.5) {
     onSurface1 = set(-@P.y,@P.x,0);
     onSurface2 = set(@P.y,@P.x,0);
     @N = abs(normalize(cross(onSurface1,onSurface2)));
     if(@P.z < 0) {  @N *= -1.0; }
} else if (@P.y == 0.5 || @P.y == -0.5) {
     onSurface1 = set(-@P.z,0,@P.x);
     onSurface2 = set(@P.z,0,@P.x);
     @N = abs(normalize(cross(onSurface1,onSurface2)));
     if(@P.y < 0) {  @N *= -1.0; }
} else {
     onSurface1 = set(0,-@P.z,@P.x);
     onSurface2 = set(0,@P.z,@P.x);
     @N = abs(normalize(cross(onSurface1,onSurface2)));
     if(@P.x < 0) {  @N *= -1.0; }


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