ProjectToCplane in Front view does not work on the polycurve in the attached file. ProjectToCplane works in Top view. The polycurve is already on the Cplane in Right view.
Can not ProjectToCplane - Front.3dm (2.8 MB)
If exploded the constituent curves project as expected.
If exploded and joined back into a single polycurve the polycurve does not project in Front view.
SelBad does not find any bad objects.
Explode yields 7 curves which is the number of visible curves.
Exploding the polycurve and SelSmall does not find any very small curves.
Another set of curves with the same problem. Can not ProjectToCplane - Front2.3dm (2.8 MB)
Hi David - the bit at the very bottom is the stopper - it would make a degenerate curve
that particular segment also fails in the separate curves version.
-Pascal
Thanks for having a look, but I’m not convinced that is the problem.
If I explode the polycurve the then ProjectToCplane in the Front view with Copy=No completes when only “bit at the bottom” is selected and the line segment vanishes. Since it is a line perpendicular to the Cplane nothing is created.
If I join the “bit at the bottom” to the adjoining lines ProjectToCplane works in the Front View. It only stops working when the large side curves are included in the polycurve.
If I split the original polycurve in the middle ProjectToCplane works in the Front View.
The “bit at the very bottom” is a simple line. The ends have identical x and y coordinates. The z coordinates of the ends differ by 3e-16. That should not cause a degenerate curve.
List results for the line: (I know, I’m only a user, not a developer so I should be looking at such advanced information. 
)
Rhino object: curve
[quote=“davidcockey, post:4, topic:131491, full:true”]
Thanks for having a look, but I’m not convinced that is the problem.
If I explode the polycurve the then ProjectToCplane in the Front view with Copy=No completes when only “bit at the bottom” is selected and the line segment vanishes. Since it is a line perpendicular to the Cplane nothing is created.
If I join the “bit at the bottom” to the adjoining lines ProjectToCplane works in the Front View. It only stops working when the large side curves are included in the polycurve.
If I split the original polycurve in the middle ProjectToCplane works in the Front View.
The “bit at the very bottom” is a simple line. The ends have identical x and y coordinates. The z coordinates of the ends differ by 3e-16. That should not cause a degenerate curve.
List results for the line: (I know, I’m only a user, not a developer so I should be looking at such advanced information. )
Rhino object: curve
DEVELOPER DEBUGGING INFORMATION ONLY
Use the Rhino “What” command.
Runtime serial number: 257
name: “”
id: 87620968-44FE-4360-9133-97E1D1E04FBD
layer index: 2
render material index: -1 (from layer)
ON_LineCurve: domain = [37.0569,37.5569]
start = (0, -0.24999999999999911, -0.89234632094775268)
end = (0, 0.24999999999999825, -0.89234632094775235)
length = 0.5
Runtime serial number: 257
name: “”
id: 87620968-44FE-4360-9133-97E1D1E04FBD
layer index: 2
render material index: -1 (from layer)
ON_LineCurve: domain = [37.0569,37.5569]
start = (0, -0.24999999999999911, -0.89234632094775268)
end = (0, 0.24999999999999825, -0.89234632094775235)
length = 0.5
Hi @davidcockey,
By projecting your 3-segment polycurves onto the construction plane of the Front viewport, the middle polyline segment becomes closed, thus producing invalid polycurves.
Does this help?
– Dale