BlendCurve
A BlendCurve is a sketchelement with geometricproperties of position, angle, curvature and curvaturerate at its startPoint and its endPoint.
See 'Smoothness' and GeometricProperties of SketchElements.
Geometric Properties of a BlendCurve sketchelement
The geometricproperties of the BlendCurve at its startPoint and its endPoint are its:
•  Position [edit with the PartEditor in the normal way.] 
If you merge the BlendPoint with other sketchelements, the geometricproperties automatically become the same geometricproperties as the adjacent sketchelements, in the default case.
You can also edit the geometricproperties to be different to the adjacent sketchelements.
If can edit the geometricproperties:
•  Exactly : with the BlendCurve dialogbox 
•  Approximately : with the BlendCurve draghandles. 

Edit the GeometricProperties of a BlendCurve
The two separators in the BlendCurve dialogbox are the:
The parameters in each separator are identical



[ or End Point ]
Angle [Units: º]:
Maximum = 360º ; Minimum = –360º
Blend checkbox:
☑  [DEFAULT] The angle of the BlendCurve becomes equal to the angle of the adjacent sketchelement at its startPoint (or endPoint) 
❑  You can edit the angle of the BlendCurve at its startPoint (or endPoint). 
Curvature k [Units:1 ∕ meters]:
Notes on curvature
All shapes, squiggles, doodles, geometric shapes are a 'curve'. All points along a curve have a radius  its 'instantaneous radius'. We call it the curve's RadiusofCurvature. I prefer to call it the 'Radius of the Curve' as that is a more literal term.
When we draw a circle that:
•  is tangential to the curve / its centre is on the normal of the curve. 
•  has a radius equal to the curve, 
...we call the circle the at that particular point along the curve. In general, the radius of the osculatingcircle continually changes as it moves along the curve, and will also flip sides where the curve changes curvature sign.
Curvature = 1 ∕ Radius of the OsculatingCircle, or more generally Curvature = 1/RadiusofCurvature
Thus, as the radius of the osculatingcircle decreases, the Curvature increases.
Curvature of a Line = 0,
Curvature of a Circle = 1 ∕ Circle Radius.
E.g. : A circle has a radius of 20mm, its curvature = 1/0.02m = 50/m.

Blend checkbox:
☑  [DEFAULT] The curvature of the BlendCurve becomes equal to the curvature of the adjacent sketchelement, at its startPoint (or endPoint) 
❑  Enter the curvature for the BlendCurve its startPoint (or endPoint). 
CurvatureRate dk ∕ ds [Units: 1 ∕ m^2]:
Notes on Curvature Rate:
CurvatureRate is the rateofchange of curvature [how rapidly curvature changes] with respect to the distance along the BlendCurve.
Only a different BlendCurve can have a CurvatureRate that is not zero. The CurvatureRate of a Line and Arc are zero.

Blend checkbox:
☑  Make the curvaturerate of the BlendCurve equal the curvaturerate of the sketchelement with which you merge the BlendCurve at the startPoint (or endPoint) 
❑  Enter a curvaturerate for the BlendCurve that is different to the curvaturerate of the adjacent sketchelement at its startPoint (or endPoint). 
Velocity Scaling
Increase VelocityScaling to 'inflate' the BlendCurve.
Decrease VelocityScaling to 'deflate' the BlendCurve.
Velocity Scaling parameter does not have units.
Default Value = 1 ; Maximum Value = 10 ; Minimum 0.01


To edit the properties of the BlendCurve with the DragHandles:
1.  Click the BlendCurve one time to show DragHandles (one click)  see mousepointer in image to the left 
Four Green draghandles show  two at the startPoint and two at the endPoint  but they are not active.
The draghandle with an:
•  Arrow: can control the VelocityScaling and the Angle 
•  Small Circle : can control the Curvature. 
You must use the BlendCurve dialog to control the CurvatureRate.


To make a DragHandle Active
You cannot drag a Green DragHandle.
An active DragHandle is Blue.
1.  Doubleclick a draghandle to make it Blue and active. 


To change the angle of the BlendCurve at the startPoint or endPoint , and also to change the overall length of the BlendCurve
1.  Drag the draghandle 
You can drag the handle in two ways.
a)  Move the arrow head further away from the Point to increase the VelocityScaling factor 
b)  Rotate the arrowhead around the Point to control its Angle. 
If you rotate the arrowhead around the Point, the Angle 'blend' with the adjacent sketchelement is broken.


To change the curvature of the BlendCurve at the startPoint or endPoint or both:
If you move the SmallCircle between 90º and ±180º
•  The Curvature increases from 0 Curvature (a straightline) to +ve 'Large Value' 
If you move the SmallCircle between 90º and ±180º
•  The Curvature increases from 0 (a straightline) to –ve 'Large Value' 
Note: the angle is always relative to the +Yaxis of the Mechanism Plane, Not the Angle of the BlendCurve.
Thus 0º is Vertical Upwards  always and will tend to make the BlendCurve 'straight' at the Point.

Smoothness and GeometricProperties of sketchelements
You frequently need a sketch to be smooth when it acts as the Path for a MotionPoint.
To join BlendCurves to other sketchelements, and other BlendCurves, and to keep the smooth, imagine that one BlendCurve is 'later' or 'after' another:
1.  Edit the BlendCurve that comes later 
2.  Select the startPoint separator in the Blend Curve dialog 
3.  Click all of the 'Blend' checkboxes 
4.  Edit the BlendCurve that comes earlier 
5.  Select the endPoint separator in the BlendCurve dialog 
6.  Clear the 'Blend' checkboxes 
Now edit the values of the endPoint.
7.  Edit the values of the endPoint of the 'earlier' BlendCurve 
As you edit the values, the startPoint of the BlendCurve that is 'later' will update to the new values you enter in the 'earlier' BlendCurve.
EXPERIMENT!
