How to draw a dart center line perpendicular to a curved waistline?

Newbies
1

Hi everyone,

I am still quite new to Seamly2D and I am currently trying to translate a patternmaking instruction from a book into a parametric Seamly construction.

The situation is about a dart on a curved waistline.

In the book instruction, the dart center point is placed on the waist curve. From this point, the dart center line should be drawn at a right angle to the waistline. So I do not simply need a vertical line downward, but a line that is perpendicular to the local direction of the curved waistline at that point.

My question is:

Is there a tool in Seamly2D to draw a normal/perpendicular line from a point on a curve?

Or do I need to approximate the tangent of the curve first, for example by using two nearby points on the curve, and then construct the perpendicular line manually from that tangent?

I have attached two images:

  1. My current Seamly2D construction, where the dart center point is already located on the waist curve. (line should be like the red line)

  2. The original patternmaking instruction from the book, where the perpendicular dart center line is shown.

I would be very grateful for any advice on the correct Seamly2D workflow for this.

image
image657×442 17.7 KB

image
image847×436 60.2 KB

1 Like
2

When you place a point on a curve, it automatically records the curve handle angles and lengths on either side of the point, although you can’t see them in the pattern, that keep the curved line true to the original curve before you added the point.

You can use the Point - Length and Angle tool to add a line to the point you created and then use the formula wizard to find the angle of one of the curve handles at A13. Then depending on the curve handle you chose, either add or subtract 90° from it.

image
image771×513 33.4 KB

I hope that this answers your question :blush:

After this step, you’re going to want to rotate the original dart closed and open up the new dart a portion, so that you have 2 darts. It will take about 2 or more rotations to achieve this, since you’re working from the centre of the dart. You will first need to find where the 2 centre dart lines meet, below the darts, to get an accurate rotation point.