Curve Length

public_public

Please suggest a method to measure the distance along a curve between specified points.

Thank you

MBartlett21

@public_public
Could you show an example

public_public

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.

NeilCooke

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 

public_public

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_sparks

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.

NeilCooke

@owen_sparks I’m guessing it may not be a 2D curve

@public_public I will post a faster solution soon

public_public

It looks like a 3D curve can not be split for some reason. The curve's split issue already arose here

https://forum.onshape.com/discussion/8706/more-tools-for-working-with-curves.

NeilCooke

@public_public - a little more involved than I first thought, but fast and accurate 



https://cad.onshape.com/documents/d103e50535cbfbf38dd6e51b

public_public

Thanks for your support!

Eleanor_Coffin

@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:
https://cad.onshape.com/documents/d8a36f7517523544158ae686/w/b257afccef639b5ffa33e3fe/e/a2254749aecfdeb3b2c601c5

tedm

NeilCooke said:

@public_public - a little more involved than I first thought, but fast and accurate 

https://cad.onshape.com/documents/d103e50535cbfbf38dd6e51b

@NeilCooke -- your script works great when measuring between two points that fall within a curve. In selecting the end points of a curve, the script returns an error.  Please see pic below.  Purely informative, although I wouldn't cry if you made a fix : )  Thank you,
Ted

NeilCooke

@ted_m_ you can use a measured variable if it's just the length of the full curve that you need. That script (which is very old) also creates the curve between the two points.