From a point to a line with exact measurements


I am new to seamly2d and have drawn a few patterns but I got stuck at a project because I cannot find a way to draw this line I need. I hope I can make it understandable what I want to ask. I’ve been trying to draw a line in this case from A3 to line A1_A2 but with exact measurement.

For example I want line A3_A4 to be 10cm and also meet with line A1_A2 but I couldn’t find a tool that does this. I’m sorry if this question was asked before on this forum, but I couldn’t find anything related. Is there a way to draw the line I need if yes does someone know how and if no will it be possible in the future? This also applies for drawing a line from a point to an arc, with exact measurements.

p.s I hope I’m posting this where I should, I’m kind of dumb with forums


Hi @ednk, welcome to Seamly!

The easiest option is to use the “Intersection point of Line and Arc” tool. That’s the blue arc, the third down on the right in your picture.

  • First it will ask you to select the first point of the line which you want the new point to be placed on.
    • bear in mind that you are placing a point at the intersection between a line & an imaginary circle perpendicular to it, so there may be two possible locations for the point. In this tool, unlike others, only the first intersection counts with no (simple) options to use the other intersection. So make sure your first point is the point you want the new point to be closest to.
  • That achieved, it will want the second point. Click it.
  • “Select point of center of arc” In this case A3.
  • A properties dialog pops up asking for the radius of the arc, which in this instance is 10cm.
  • click OK & you’ve done it!
    • you may have noticed that the dialog had drop-down menus showing the points you had selected. If you realize that you wanted A4 closer to A2, but had started by clicking A1, you can right-click A4 & open the properties editor again to switch A1 & A2. fairly often the pop-up properties dialog is more powerful than the side-bar properties dialog.

I hope that’s more helpful than confusing! I’m at least sure it’s better than Trigonometry, which is what I used the first time I should have used this tool. :fearful:



Keeping in mind there may be 2 points of intersection.

This actually was a common way to do it the old fashion way with pencil, paper, and a compass. One would set the radius on the compass against a (scale) ruler, using what ever center point, swing a mark across a line you want to intersect… it’s easier than trying to measure with the ruler to find the point. Of course there was always some measure of error… which is why blue prints were not meant to actually be measured - measurements were always provided in the drafting. :slight_smile:


@Pneumarian Thank you, i love seamly so far! And thanks, it worked! Can’t believe i haven’t tried that tool, or I did and I used it the wrong way.

@Douglas yes that’s how i did it now when i tried to draw a line to a curve/arc. Because using the tool @Pneumarian said will draw a straight line for me if this point I want is on a curve/arc.