I am having troubles creating a 90 degree vector from a point. Here is my current attempt, showing the vectors parallel to the ground plane:

I am struggling to achieve a 90 degree between vectors `a`

and `b`

. Basically, I need blue and yellow vectors be parallel to each other, both at 90 degree to `a`

. My current code:

```
left = new pc.Vec3(-0.5, 0.4, 0);
right = new pc.Vec3(0.5, 0.4, 0);
var dir1 = right.clone().sub(left);
var dir2 = left.clone().sub(right);
var leftSide = new pc.Vec3().cross(dir2, pc.Vec3.UP);
leftSide.y = left.y;
var rightSide = new pc.Vec3().cross(dir1, pc.Vec3.DOWN);
rightSide.y = right.y;
```