# Torus part

Hi
I’m creating torus like this:
ON_Plane plane(ON_origin, ON_zaxis);
ON_Circle circle(plane, R);
ON_Torus torus(circle, r);
ON_Brep* brep = ON_BrepTorus(torus);
But I want just a part of it. Let’s say I have a span angle and I want just that part of the torus to get…How can I achieve this?
Filip

I suppose you have two options.

1. Create the Torus and then trim away the excess.

2. Create an arc with the given span angle. At the start and end create a circle of radius `r` perpendicular to the direction of the arc. Use Sweep1 to create a torus part over the arc (rail) using the circles as cross section curves.

My preference would be 2.

Thanx Menno, I’m trying the second…but I’m a little confused wit using RhinoSweep1()…

Maybe this example will help

Did you know how to create circle normal to the arc at start or end point?

I guess like this:

``````double r; // circle radius
ON_Arc a; // arc

double t0 = a.Domain().m_t[0];
double t1 = a.Domain().m_t[1];

ON_3dPoint o = a.PointAt(t0);
ON_3dVector n = a.TangentAt(t0);

ON_Plane p0(o, n);

o = a.PointAt(t1);
n = a.TangentAt(t1);
ON_Plane p1(o, n);

ON_Circle c0(p0, r);
ON_Circle c1(p1, r);

// sweep over a, using c0 and c1
``````

I try like this
double teta = 3.14/2;

``````ON_Circle median_circle(ON_xy_plane, R);
ON_Arc arc(median_circle, ON_Interval(-teta/2, teta/2));

double t_s = ON_UNSET_VALUE;
double t_e = ON_UNSET_VALUE;
arc.ClosestPointTo(arc.StartPoint(),&t_s);
arc.ClosestPointTo(arc.EndPoint(),&t_e);
ON_3dVector tan_s = arc.TangentAt(t_s);
ON_3dVector tan_e = arc.TangentAt(t_e);
ON_Plane p_s(arc.StartPoint(),tan_s);
ON_Plane p_e(arc.EndPoint(),tan_e);
ON_Circle circle_s(p_s, r);
ON_Circle circle_e(p_e, r);
``````

but your solution is more elegant Thank you a lot…best wishes