SetArcLength.py

import rhinoscriptsyntax as rs
import scriptcontext as sc
import Rhino

def SetArcLength():
    
    def arc_filter( rhino_object, geometry, component_index):
        return geometry.IsArc()
        
    looped = False
    while True:
        length = 1
        if sc.sticky.has_key('ARC_EX_LENGTH'):
            length = sc.sticky['ARC_EX_LENGTH']
        go = Rhino.Input.Custom.GetObject()
        strMessage = "Pick the end of the arc to move."
        if looped: strMessage = "Pick the end of the arc to move. Press enter to finish."
        go.SetCommandPrompt(strMessage)
        go.GeometryFilter = Rhino.DocObjects.ObjectType.Curve
        go.SetCustomGeometryFilter(arc_filter)
        opLen = Rhino.Input.Custom.OptionDouble(length)
        go.AddOptionDouble("Length", opLen)
        go.AcceptNumber(True, False)
        go.EnablePreSelect(False, True)
        rc = go.Get()
        
        if go.CommandResult() != Rhino.Commands.Result.Success:
            return go.CommandResult()
            
        if rc == Rhino.Input.GetResult.Option:
            length = opLen.CurrentValue
            sc.sticky['ARC_EX_LENGTH'] = length
            continue
            
        if rc == Rhino.Input.GetResult.Number:
            length = go.Number()
            sc.sticky['ARC_EX_LENGTH'] = length
            continue
            
        if rc == Rhino.Input.GetResult.Object:
            objref = go.Object(0)
            geo = objref.Geometry()
            selPt = objref.SelectionPoint()
            
            p_rc, par = geo.ClosestPoint(selPt)
            
            flip = False
            if p_rc:
                if par>= geo.Domain.Mid:
                    flip = True
                    print geo.Reverse()
                    
                a_rc, arc = geo.TryGetArc()

                crntSweep = arc.AngleDomain
                
                radius = arc.Radius
                x = abs(length)/radius
                
                if flip:
                    
                    if length > 0:
                        sweep = Rhino.Geometry.Interval(-x, 0)
                    else:
                        sweep = Rhino.Geometry.Interval( crntSweep.Max , crntSweep.Max+x)
                        flip = False
                else:
                    if length > 0:
                        sweep = Rhino.Geometry.Interval(crntSweep.Max-x, crntSweep.Max)
                    else:
                        sweep = Rhino.Geometry.Interval(crntSweep.Max, crntSweep.Max+x)
                        flip =True
                arc.AngleDomain = sweep
                if flip:
                    arc.Reverse()
                arcCrv = Rhino.Geometry.ArcCurve(arc)
                sc.doc.Objects.Replace(objref, arcCrv)
                print "Arc length set to " + str(round(length, 3))
                looped = True
                sc.doc.Views.Redraw()
            continue
    
if __name__ == '__main__':SetArcLength()