Trimming to a point?

Trying to understand the way TRIM works when you use modifier buttons.

In the picture below, I drew line 1 straight down. Then, I drew another straight line (2) next to it that was shorter. I used TRIM and the endpoint modifier on line 1 when prompted for "trim to point". As you can see by the red reference line (and checked via LIST), it trims to the exact Y of line 1.

I drew line 3 at an arbitrary angle, finishing it short of the reference line. I did the above procedure, but it overshoots the reference line.

Next, I drew line 4 parallel to line 3, and left it short as well. With this TRIM, I used the @Ref. Point modifier and selected line 1 with the endpoint modifier, and then clicked after selecting the Same Y modifier. This got it closer to the reference line, but it still overshoots it.

I know I can just TRIMTO the reference line and get it bang on, but for the sake of understanding the mechanics, does anyone know (hint: Monsen) what TRIM is hunting for in the above scenarios when the TRIMmed line is at an angle?

Thanks in advance.


  • MonsenMonsen 🖼️ 43 images Mapmaker Administrator
    edited May 20
    When you trim to a point, and you choose a point that is not on the actual entity, CC3+ will use the point on the entity that is closest to the point you selected. (Since trim can extend the line too, saying the point is on the entity is a bit of a misnomer, more formally correct would be to say on the line described by the line segment in the drawing)

    If you do some measuring on your drawing there, you'll see that the trim points used for both 3 and 4 are closer to the endpoint of 1 this way than if they had been trimmed at the reference line.
  • LoopysueLoopysue 🖼️ 10 images Mapmaker ProFantasy
    So both those lines are trimmed at the precise point where (if they were tangent lines) they would meet the smallest imaginary circle drawn at the trimming point that they could possibly meet?
  • MonsenMonsen 🖼️ 43 images Mapmaker Administrator
  • Thanks! Makes perfect sense now.
  • 4 months later
  • Reviving this post to ask a related question. See this diagram:

    I think the mechanics are the same as already explained up the thread. I've tried setting the reference point to the endpoint of the existing line and then snapping to Same X, but this has the offset effect described in the explanation a few messages up. Is there a way to do this with a combination of snaps while drawing the parallel line, or is the only way to draw a straight line up from the endpoint of the existing line and trimming to it? No huge deal if it is, just wanting to know the fastest workflow.

    Thanks in advance.

  • MonsenMonsen 🖼️ 43 images Mapmaker Administrator

    I don't think it is possible to combine those modifiers like that. I tried a couple of combos to try to get what I wanted, but I couldn't get a good result.

    If the line is supposed to have the same x for both start and end, you could just copy it instead, with Ortho enabled.

  • Thanks, Monsen. Yeah, I tried every combo I could think of. I'll either do the ortho copy or use construction lines.

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