Curve (point,point,angle,angle)

curve
Most of the pattern drafting - side seams, necklines, armholes, sleeve caps, collars, hems of flared skirts - is about curves.

Let's draft the first two curves in our skirt pattern - these will be the sections of the side seams from waist to hip level. 

As usual, we recommend having a look at the documentation on curve command and YouTube video on curves.

Here's the code we are going to use for the back side seam:

// side seam
back_side_skirt=curve(ws2,h,[ws2:h].a1-5,-90)

The first curve, back_side_skirt, goes from point WS2 to point H.


It departs from WS2 almost in the direction of point H, but just a bit higher than that. The formula says [ws2:h].a1-5 degrees - we used the angle from WS2 towards H, and then moved 5 degrees counterclockwise for a smoother curve. At point H, the end point, this curve is directed upwards - at -90 or 270 degrees.


The blue arrow in the sketch above shows the direction from WS2 towards H, and the red arrow shows the starting angle of the curve, in 5 degrees from the blue one. 
The green line shows the ending angle of the curve.

For the front side curve we are using a similar code:

front_side_skirt=curve(h,ws1,-90,[ws1:h].a1+5)

The curve starts at point H and goes upwards. It arrives at point WS1, where it is headed almost in the direction of point H, just 5 degrees higher.



You can see the tiny control points of a curve that show the directions of its angles.

It is at this moment when you start wondering - why do I need to use the formulas? Why can't I simply drag and move the control points and make a smooth curve? The answer is in grading. Let's see how the curves change depending on the sizes and grade for this (future) skirt across various waist and hip values, for the same height.

1) Waist = 65 cm, hips = 102 cm


2) Waist = 76 cm, hips = 102 cm

3) Waist = 88 cm, hips = 102 cm

4) Waist = 96 cm, hips = 102 cm

The curves that form the side seams are very different. It would be super annoying to adjust their direction and their slope for every single individual case, and you are not required to. Once you get the formula in place, the rest is done by parametric drafting.


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