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Curve Length

public_publicpublic_public Member Posts: 5
Please suggest a method to measure the distance along a curve between specified points.
Thank you


  • MBartlett21MBartlett21 Member, OS Professional, Developers Posts: 2,010 EDU
    Could you show an example
    mb - draughtsman - also FS author: View FeatureScripts
  • public_publicpublic_public Member Posts: 5
    FeatureScript 920;<br>import(path : "onshape/std/geometry.fs", version : "920.0");<br><br>annotation { "Feature Type Name" : "CurveLength" }<br>export const CurveLength = defineFeature(function(context is Context, id is Id, definition is map)<br>    precondition<br>    {<br>        annotation { "Name" : "Point_1", "Filter" : EntityType.VERTEX, "MaxNumberOfPicks" : 1 }<br>        definition.Point_1 is Query;<br><br>        annotation { "Name" : "Point_2", "Filter" : EntityType.VERTEX, "MaxNumberOfPicks" : 1 }<br>        definition.Point_2 is Query;<br><br>    }<br>    {<br>        var myStartPoint is Vector = evVertexPoint(context, {<br>                "vertex" : qNthElement(definition.Point_1, 0)<br>            });<br><br>        var myEndPoint is Vector = evVertexPoint(context, {<br>                "vertex" : qNthElement(definition.Point_2, 0)<br>            });<br>        var myCurveF is Query = qContainsPoint(qEverything(EntityType.EDGE), myStartPoint);<br>        var myCurve is Query = qContainsPoint(myCurveF, myEndPoint);<br>        var Length_1 is ValueWithUnits = evLength(context, {<br>                "entities" : myCurve<br>            });<br><br>        debug(context, Length_1);<br><br>    });<br><br>

    "evLength" only evaluates total length. But I need calculate the length between any points on the curve.

  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 4,308
    I’d be interested in a solution to this. All I can think of is to:
    1. Iterate over the curve to find the parameter closest to each point using evEdgeTangentLine
    2. Compare parameters against overall curve length 

    Director, Technical Services, EMEAI
  • public_publicpublic_public Member Posts: 5
    Currently I'm using the same approach. But looks like it is a little bit slow. evLength works faster. I iterate over 10 000 points to get necessary tolerance. It is nice to get the reverse function to evEdgeTangentLine.

  • owen_sparksowen_sparks Member, Developers Posts: 2,660 PRO
    edited October 2018
    Could you project it onto a new temp sketch, split it, measure it, delete the sketch?  No iterations that way.  Edit - Dumb Idea

    Owen S.
    Business Systems and Configuration Controller
    HWM-Water Ltd
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 4,308
    @owen_sparks I’m guessing it may not be a 2D curve

    @public_public I will post a faster solution soon
    Director, Technical Services, EMEAI
  • public_publicpublic_public Member Posts: 5
    It looks like a 3D curve can not be split for some reason. The curve's split issue already arose here

  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 4,308
    @public_public - a little more involved than I first thought, but fast and accurate 


    Director, Technical Services, EMEAI
  • public_publicpublic_public Member Posts: 5
    Thanks for your support!
  • Eleanor_CoffinEleanor_Coffin Member Posts: 43 ✭✭
    edited February 22
    @NeilCooke or anyone who knows enough about FeatureScripts -- (I'm learning but I'm not that familiar yet!), if you had a chance would you be able to make it so that FS saves the curve length value in a new variable?

    Basically I'm modeling a drive belt with two different-sized pulleys, so I want to measure the exact length of the belt and then save use that length in the part number -- so if anyone knows of a different way to do that, I'd be open to that too. Thank you!

    Posted too soon, just found a FS that does exactly what I'm asking:
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