3D problem

This is a problem I've got.

Got a 3D line structure and I want to draw a curve in a plane intersecting the line structure from one particular point in that plane to another, snapping on lines where they ntersect that plane.

Can I define a sort of sectionplane in which I can draw and snaps are only in that plane?

The problem now is when I choose some plan view, the cursor snaps on lines that are out of the plane I want to draw in.

This plane I want to draw in can be any orientation or inclination.

There is the OSNAPZ system variable that will project osnap points to the current UCS, but I’m not sure that is what you are describing.

The request sounds more like - snap to point where a curve penetrates a plane with some arbitrary orientation – then I would have to say no, there is no native object snap (or other command) for that in vanilla AutoCAD.

If the curves are all linear then the plane intersection coordinates could be retrieved with CAL’s ilp(p1,p2,p3,p4,p5) function. If numerous lines with numerous planes needed to be processed then that method would likely be rather labor intensive, I imagine.

The process could be automated with one of the available APIs (AutoLisp, .Net, VBA [though, if the curves in question are 3d splines, the process gets a bit tricky]). Perhaps if you posted an example file some of the resident coders would take an interest.

I often have to draw curves (guides and shapes for lofting) that are planar (I think that's the wright word) is to say all the points of those cuves are in a plane. This plane can be any plane with any orientation and the curves must start and end on other objects intersecting this plane. I don't know how to do this.

.. curves must start and end on other objects intersecting this plane. I don't know how to do this.

If you know 3 points (other method are avialable) UCS to create the "plane" you want to work on.

Yes I think I found it, my error was that I didn't switch "planar" on.

Ok move the UCS in the plane you want and put "planar" on to stay parallel with the xy plane. At least in Rhino it works.

Well I allready had some suspicions it was simple because it's so unavoidable.

OOPS Acad has no "planar"

Or at least cannot find it.

There is also an ever being problem with snapping on curves.

It snaps besides them and then lofting doesn't work ofcourse.

I don't know how I have to make it work, but why do I know how to make it work in Rhino, a program that I 've allready been using for 2 hours? And lofting and sweeping allways works in Rhino and in Acad almost never, always searching in every step I take why it doesn't work with non documented error messages.

I guess Rhino is a program for dummies like me.

Rhino was designed with a focus towards this type of “freeform” modeling and, as such, is a lot more compliant with the input curves. Once an operator gets used to AutoCAD’s particular requirements, though, similar shapes are possible.

If you are looking for the same functionality as Project Object Snaps (with the Planar mode set) in Rhino then investigate the OSNAPZ system variable in AutoCAD.

AutoCAD has no direct ability to generate points at a Curve/Plane intersection. Workarounds are required.

I checked out OSNAPZ and this is what I did.

I setup a UCS defining the plane I want to work in.

Then i go to plan view.

Set OSNAPZ to 1 and draw the curve, I notice a certain restriction in the snapping.

On screen everything looks good. I loft the curves and get the message that the guides (the 2 curves I drew the curve between) do not intersect. Looking closely I see things that do not match , and I can't seem to make them match.

Alltogether this is an ongoing merrygoround.

OK, I use Autocad for several years meanly in 2D, say about 2 monts a year for designing modell airplanes, once every 18 months or so, pure for a hobby.

I bought a more beefy PC to be able t do 3D, have been fiddling 4 weeks now to get something done, and I got something done, not quite good but something because I was determined to stay with Autocad aslong it wasn't certain that it's not fit for the job. I 'm evaluating Rhino and got the thing done after 2 hours and never used it before. Even when it's true that Rhino is a bit Autocad alike in terms of user interface, I think this is a strong indication that it's not fit to do what I have to do.

Maybe that's the reason Autodesk introduced Inventor.

2D ok, relatively simple 3D OK but complex curvature 3D it sucks.

Thanks a lot for the input, it was very helpful anyway.

You may be right !