Project intersect of Intersection curve works but does not update correctly

[mr.rickwright]

This has a few steps so bear with me!

create curve1 on xy plane 

create curve2 on yz plane

create Intersection curve of these two on third plane, say xz or any construction plane.

now use project intersect to a sketch on plane 4.     

EVERYTHING WORKS UP TO THIS POINT.

NOW - change a dimension on curve 1 or curve 2 and the sketch on plane 4 gives error of "missing curve"   I don't think this should happen.    it is the Intersection Curve that is giving the problem.

[mr.rickwright]

attached file because I can't recreate the problem in a simple design

[laughingcreek]

I run into this from time to time also, and agree it shouldn't happen.  I think, but don't know, that the internal id for first projection gets recalculated/changed under certain conditions, and subsequent projections down stream lose the reference as a result. 

this behavior is one of the reasons one of my personal guidelines is to not make projections of projections. 

A work around is to project from the original lines and use construction lines to locate the point.

another workaround is to use surfaces (surfaces are frequently a better choice anyway because the edges will tend to have better curvature quality than projected lines.)

attached is a simple example using all three approaches.  the referance gets lost fairly easily when dragging around the points on the reference splines.

and a screen cast of the example model-

https://knowledge.autodesk.com/community/screencast/df42a06c-cd45-499d-809e-0e9da2f9794e

@jeff_strater - what do you think?  a bug?  

[TrippyLighting]

I never ever work with that project intersect abomination.

Projections of spines that are not perpendicular to the original sketch plane, offset splines and project/intersect create in most cases broken curvature such as shown in the image below:

I have come across only one case where working with intersected and trimmed faces did not work and I all cases where it did work it created edges with improved curvature. 

One might argue that curvature isn't important in a model. That is until an edge does just not want to get filleted 😉  

[TrippyLighting · Accepted solution]

Hre's what I mean with that:

 

While quality oo the input curves could use some improvement to reduce these waves, the curvature is smooth.

Also, when the edges are intersect-projected into the profile sketches, they update properly. 

I actually just had to use the "manage lost projections" tool to get that fixed in short order. @jeff_strater that tool works brilliantly!

[mr.rickwright]

Thanks for the tip on "manage lost projections"    Brilliant!

I guess i'm going to have to practice with surface intersects.    It definitely produces an improved curve.

It does seem a pity to have to create a surface just to create a decent rail for another surface.

[mr.rickwright]

Alex; thank you very much two great tips - I can see a use for both workarounds.   In my case I am constructing a rail for a subsequent loft so good curvature is important, so I will use the intersecting surface approach but will keep the construction line trick in my back pocket for future instances when I just need the points.

I really appreciate the support of the folks on this forum;  there is basic learning of how the tool should work then there is a WEALTH of knowledge on how to work around the foibles and idiosyncrasies.  
Thanks again

Rick W

[mr.rickwright]

Peter; thank you.  I practiced with the surface intersect.

I didn't trim the surface just extruded  the first surface the size of the max expected movement of the second curve then extruded the second curve to object (using the first surface as the target object) Then I could project 3d the joint between surfaces.   So far so good!

I think this is the last "brittle" piece of my parametric kayak.    I am now pretty comfortable that I can adjust user parameters to drive the custom design.

Next I have to play with simulation to predict specifications and performance! (might need to learn Python for some of that)

You and other members of this forum have been invaluable in helping me overcome the foibles and idiosyncrasies of the tool. 

Thank you.

Rick W