The cyan and yellow shapes are planar but not aligned with the view (Front).
I want to draw a line in the same plane as the object highlighted in yellow that follows part of the blue line segment.
I have done both CPLANE by OBJECT and CPLANE by 3 Points and have enabled PRojOSNAP.
When I try to trace the cyan line in the CPLANE the line is always set (In red here). How can I get the line to be aligned with the cyan line from the perspective of the front view and have the line lie in the CPLANE defined by the yellow shape?
Here is what I would do. Create a CPlane with 3 points on the yellow lines. Create a surface on the CPLane large enough to cover the cyan objects when looked at in front view. Go back to your regular (world?) front view CPlane. Project the cyan curves onto the newly created surface, “Project” will use the CPlane as reference for the direction of the projection.
Delete the surface.
You can also use the command _Plan once you’ve drawn your CPlane with 3pts which sometimes helps to understand what’s happening when you’re drawing on the CPlane.
Open another viewport though before you _Plan otherwise you’ll loose one of the views you already had set up.
In this case I would not do that (setting the camera perpendicular to the Cplane), since the objective is to create a new surface covering the cyan objects in Front view.