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coincident vs. pierce

rune_thorsen229rune_thorsen229 Member Posts: 182 EDU
in Using Onshape
john_mcclary I found use for pierce. Still I do not fully understand why there have been implemented two types of constraints: coincident and pierce that fundamentally seems to do the same?.
Why is coincident not simply implemented as a pierce when the planes differs?

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Comments

  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 5,689
    Pierce is used when you want to make a sketch entity coincident to the point where external geometry intersects the current sketch plane. Coincident is for "projected" geometry only. We could solve behind the scenes and call it all coincident, but the two types are there to make it clear which type of geometry you are referencing.
    Senior Director, Technical Services, EMEAI
  • rune_thorsen229rune_thorsen229 Member Posts: 182 EDU
    edited March 2020
    Found this old one: January 2015brucebartlett .  I tried to make some experiment that illustrates the difference. The only difference I can find is that coincident does not always work and then I resort to pierce (as john_mcclary) taught me. 
    @NeilCooke sooner or later a student or collegue will ask me so could you please provide an example of the functional difference?
    Thanks in advance
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 5,689

    Senior Director, Technical Services, EMEAI
  • rune_thorsen229rune_thorsen229 Member Posts: 182 EDU
    edited March 2020
    NeilCooke. It moves the line so it touches the wave. How would a coincident behave differently?
    What I mean exactly is that the Pierce does what the word 'Coincident' says, whereas Coincident behaves more like a projection.

    Dashed line: coincident (with the plane)
    Solid: pierce
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 5,689
    That point is now fixed - looking at it from the front it looks like it is coincident to a vertical line and therefore should be able to slide up and down. 
    Senior Director, Technical Services, EMEAI
  • rune_thorsen229rune_thorsen229 Member Posts: 182 EDU
    NeilCooke , I don't fully understand. Could you provide the animation to confront with?
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 5,689
    https://cad.onshape.com/documents/36758a4ca8d3bbab9cd1474a/w/7b2a62ef43f244c973242d55/e/a6f69d292ce778aae9188c75
    Senior Director, Technical Services, EMEAI
  • rune_thorsen229rune_thorsen229 Member Posts: 182 EDU
    Hmm, maybe I should have cited January 2015 brucebartlett  "Most people don't understand the difference between pierce and coincident in a sketch and I don't see the need to separate these into 2 different constraints."
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