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# Curve from projections

Member Posts: 6

Let's create two vectors (using bridge curves) `V1` and `V2`. There aren't parallel or anti-parallel.

Let's then create two planes (via mid-plane, or line-angle) `P1` and `P2`. Then, we draw two curves `C1` and `C2` upon these planes.

Is there a way to compute the final 3D curve `Cf`, such that these two curves `C1` and `C2` will be the projections of` Cf` upon `P1` and `P2`?

For reference, we can do this on freecad using Curve Workbench→ Mix Curves. Thank you

• Moderator, Onshape Employees Posts: 5,574
edited September 5

Can you create a document manually to show what you are trying to achieve. Initial gut feel is no, not in a single step without FeatureScript.

Senior Director, Technical Services, EMEAI
• Member Posts: 6

Ok, to clarify: If i create a document in onshape mimicking what I want to do, would that suffice?

As I dont know how to do what I want to do on OnShape, actually doing it is out of question

• Member, Onshape Employees Posts: 170
edited September 6

It's a pretty abstract description but I've made something - perhaps you can tell us if it is correct or not…

The orange curve (Cf) is the 3d projection of C1 and C2 which are on P1 and P2 respectively.

• Member Posts: 6

YES that is where I am trying to go - In the first and second examination it looks perfect.

However I'd also like to know, if there's a tolerance/error in the result that is inherent to the calculation that onShape does.

• Member, Onshape Employees Posts: 170

The projection is very accurate, within the very tight tolerance of the modeling kernel. The curve resulting from the projection of 2 sketches is calculated by the intersection between extruded surfaces. This intersection curve will (likely) be a multispan deg3 curve. (For trivial cases of projecting 2 line segments, the projection will also be a line/deg1 curve). You can experiment by reprojecting the intersection back onto a plane and see no loss of original fidelity.

• Member Posts: 6

Thank you.

Now, and actual application:

Consider the planes: Plane_TEST_00 and Plane_TEST_01, and the curves CURVE_00 and CURVE_01.

I select projected curve; and then select "two curves" - and then choose the curves CURVE_00 and CURVE_01 as the two sketches. This fails the generation.

If i modify the curves to be more "rounded", i.e, make the turns softer, it will work out.

That leads me to the next question:What limitations should I take into mind for applying this procedure? Thank you.