Cut (object,point,direction,1st part,2nd part). Delete(objects).

cut
Okay, we now we have a nice smooth waistline with a closed dart. But how do we open it? On paper, we would cut this block and open the dart physically.


The green section would stay in place, and the red section would be moved. We are going to do exactly the same, only using parametric drafting commands.

First, let's check to see if we have all the objects defined. We defined the point in the corner, WS2, and we defined the side seam, BACK_SIDE_SKIRT. What we don't have, is the green and the red sections of the waistline, as it is presently one curve. 


So - let's cut it! Here's a link to documentation on the cut command.

We start cutting from R2, and we cut in the direction of R120. We already know how to define directions between two points - it is [r2:r120].a1.

The object that we cut is back_waist, and we want to place a point at this point and define two parts of the back waist, the one closer to center back, and the one closer to the side seam. Here's the code:

R12 = cut(back_waist,r2,[r2:r120].a1,back_waist_center,back_waist_side)
The parts of an object to be cut are defined along its direction. Back_waist goes from W2 towards WS2, so the first part is closer to the center, and the second part is closer to the side seam.


Now we can rotate WS2, BACK_WAIST_SIDE, and BACK_SIDE_SKIRT back in place - open the dart.

// open back dart
rotate((ws2,back_side_skirt,back_waist_side),r2,angle(r120,r2,r110))


I am missing a point for the upper corner of the back dart that is closer to the side seam. R120 and R110 are no longer relevant, as they don't lie on the waistline. I am going to use the same rotate function, but this time I will tell the program to create a new point with a specific name as a result:

rotate((r12),r2,angle(r120,r2,r110),(r11))


 My screen has become too busy. We can get rid of R120 and R110, as we now have the precise position of the dart points on the waistline . That's easy to do using the delete command (documentation on delete is here).

delete(r120,r110) 


I shall repeat these operations for the front skirt:

// open front dart
rotate((ws1,front_side_skirt,front_waist_side),v2,-angle(v120,v2,v110))
rotate((v11),v2,-angle(v120,v2,v110),(v11))

delete(v120,v110)


The "extra" parts of the curves next to darts are parts of back_waist and front_waist curves. We may delete them as well, for a clearer draft:

delete(back_waist,front_waist)


Or we may leave them in place, in case there's some further manipulation planned (think yoke, or A-line skirt with closed darts).

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