Windows only

Demonstrates how to compute the radius of curvature of a curve object at a selected location.

CRhinoCommand::result CCommandTest::RunCommand( const CRhinoCommandContext& context )
{
CRhinoGetObject go;
go.SetCommandPrompt( L"Select curve for curvature measurement" );
go.SetGeometryFilter( CRhinoGetObject::curve_object );
go.GetObjects( 1, 1 );
if( go.CommandResult() != success )
return go.CommandResult();

const ON_Curve* crv = go.Object(0).Curve();
if( 0 == crv )
return failure;

CRhinoGetPoint gp;
gp.SetCommandPrompt( L"Select point on curve for curvature measurement" );
gp.Constrain( *crv );
gp.GetPoint();
if( gp.CommandResult() != success )
return gp.CommandResult();

ON_3dPoint pt = gp.Point();

double t = 0.0;
if( !crv->GetClosestPoint(pt, &t) )
{
RhinoApp().Print( L"Failed to compute radius of curvature.\n" );
return failure;
}

ON_3dVector tangent = crv->TangentAt( t );
if( tangent.IsTiny() )
{
RhinoApp().Print( L"Failed to compute radius of curvature. Curve may have stacked control points.\n" );
return failure;
}

ON_3dVector curvature = crv->CurvatureAt( t );
const double k = curvature.Length();
if( k < ON_SQRT_EPSILON )
{
RhinoApp().Print( L"Radius of curvature: infinite.\n" );
return failure;
}

ON_3dVector radius_vector = curvature / (k * k);
ON_Circle circle;
if ( !circle.Create(pt, tangent, pt + 2.0 * radius_vector) )
{
RhinoApp().Print( L"Failed to compute radius of curvature.\n" );
return failure;
}