VEX rotation

[BcM]

Hello,

I just started with Houdini, and tried to make a sweep kinda thingy with VEX (part of a larger plan). I cannot seem to figure out how to get around this problem. When I scatter points around my existing point, they are not rotated, I assume because the points I drew have no normal whatsoever. I want them like the red lines in the attachment.

I tried to do a lookat from one point to the next, but I cannot figure out what to do next.

//define variables
float twopi = 3.14159 * 2;

float theta = 0;
float step_angle = twopi / (float)85;

float x, z;
vector pos;
matrix n;

// define line rotation

// add points
while(theta < twopi)
{
    x = @P.x + cos(theta) * .05;
    z = @P.z + sin(theta) * .05;
    
    pos = set(x, @P.y, z);

    addpoint(0,pos);
    
    theta += step_angle;
}

 

Any help would be appreciated.

 

 

 

 

[f1480187]

Do you want it to be perpendicular to the plane created by two edges with angle? For any non-corner case you can compute rotation matrix:

// Point wrangle.

// Compute matrix aligned with plane created by two edges.
vector e0 = point(0, "P", @ptnum-1) - @P;
vector e1 = point(0, "P", @ptnum+1) - @P;

vector y = normalize(e0 + e1);
vector z = normalize(cross(e0, e1));
vector x = normalize(cross(z, y));
3@r = set(x, y, z);

After that, you may use it in your point creation loop like this:

// Create position on circle centered at the origin.
// Scale it by radius. Rotate it by rotation matrix.
// Translate it to desired location.
set(cos(theta), sin(theta), 0) * radius * r + pivot

It's an example expression, not a final code. From your code, value .05 can be used as a radius, @P can be a pivot and r is a matrix computed by the snippet above. There are common cases where it will not work. You should decide which orientation to prefer from infinite possible variants:

1. End points.
2. One or both edges has zero length.
3. Angle between edges is 0 or PI

 

align_circles_to_curve.hipnc