public Nullable<double> Distance {get;}

if (cogoLine.IsStraightLine)
{
  var dist = cogoLine.Distance;
  var dir = cogoLine.Direction;
}
else if (cogoLine.IsCircularArc)
{
  var circArcDefinition = cogoLine.ToCircularArcDefinition();
  string s = "";

  //show Arc length, either entered or calculated
  if (circArcDefinition.IsDefinedByArcLength) 
  {
    if (circArcDefinition.ArcLength.HasValue)
    {
      s += "<entered> Arc Length: " + circArcDefinition.ArcLength.Value.ToString("F3")
        + Environment.NewLine;
    }
  }
  else
  {
    if (circArcDefinition.CanCalculateArcLength())
    {
      s += "<calc> Arc Length: " + circArcDefinition.CalculateArcLength().ToString("F3")
           + Environment.NewLine;
    }
    else
      s += "<calc> not able to calc arc length." + Environment.NewLine;
  }

  // chordLength
  if (circArcDefinition.IsDefinedByChordLength)
  {
    if (circArcDefinition.ChordLength.HasValue)
    {
      s += "<entered> Chord Length: " + circArcDefinition.ChordLength.Value.ToString("F3")
        + Environment.NewLine;
    }
  }
  else
  {
    if (circArcDefinition.CanCalculateChordLength())
    {
      s += "<calc> Chord Length: " + circArcDefinition.CalculateChordLength().ToString("F3")
           + Environment.NewLine;
    }
    else
      s += "<calc> not able to calc chord length." + Environment.NewLine;
  }

  // central Angle
  if (circArcDefinition.IsDefinedByCentralAngle)
  {
    if (circArcDefinition.CentralAngle.HasValue)
    {
      s += "<entered> Central Angle: " + circArcDefinition.CentralAngle.Value.ToString("F3")
        + Environment.NewLine;
    }
  }
  else
  {
    if (circArcDefinition.CanCalculateCentralAngle())
    {
      s += "<calc> Central Angle: " + circArcDefinition.CalculateCentralAngle().ToString("F3")
           + Environment.NewLine;
    }
    else
      s += "<calc> not able to calc Central Angle." + Environment.NewLine;
  }
}