Hi Rado, I'm not entirely sure if I understand but you can draw in some lines and use Construct > Curve > Project to project those onto your object, that is another way to generate section cuts. Or if you have already created planes that intersect the piece, use Construct > Curve > Isect to create curves where the planes intersect the object. Either of these methods will give you curve output directly.

Then if you want the results squished down to a plane, go to a side view and use the edit frame to squish them down by doing a 1D type scale.

That looks something like this:

Set up some lines (you can use Transfrom > Array > Dir to make equally spaced copies):



Project those lines onto the shape:



Now from a side elevation view, grab the edit frame handle here:



And move it downwards until you get the "Flat" snap:



Is that the kind of thing you're trying to do?

- Michael

Not sure if that helps me (although I think that 'flat' feature might be heading in the right direction of what I need). I took some screen shots to clarify my question.

-I constructed the object in shot #1 and it's currently only one giant solid (no curves or any other type of geometry).

-I then take a rectangle and make a plane in the location where I want to draw my section cut (as seen in shot #2).

-Using boolean difference, I divide the solid object and remove the portion that's behind the section cut. I'm left with what's shown in shot #3.

-I then align the cut part of the object to a known view (in this case the front view, as shown in shot #4). Only having a solid to work with, I've had to trace over the outline of the object. I'm only interested in getting the lines that would show up from this section cut (I'm not interested in hidden lines that are behind objects). You can see that I've started tracing the shape in shot #4.

-Shot #5 shows a finished tracing of a section cut. When you trace stuff from a view, not all of the lines line up on the same 2d plane, so I've been using the align command to get them all on the same plane (important for importing into other programs)... (Your 'flat' trick will make this part faster).


So, is there any way to make this process faster? I was hoping that there would be a way to take a solid and somehow derive all of the lines that were used to create the solid. If I could somehow do that, I could take all of those curves / lines and flatten them into one view and then trim the hidden lines as needed.

I hope this is clearer! Thanks again for your help!!!!

Rado

Hi Rado, I'm sorry but I'm still not quite fully understanding. I'm getting a bit lost when you get to the tracing part - it looks like you want to create some curves that are not only in that plane that you cut with but also some of the pieces that are behind it as well?

Instead of tracing those by drawing new 3D curves, you could instead save out to AI format which will produce a flattened 2D snapshot of the edges in your model, it seems like that would produce the flattened traced curves that you want?

If you want to produce that slanted section as the sort of "level" reference, then you could use Orient to align that face to the Top, Front, or Right views, and then when you export to .AI format there is a choice of which view you want to export so you can use the one you aligned to. Or it is also possible to do the reverse and keep your model in the same spot and instead re-orient the Top/Front/Right views to be looking down at a particular face, you can use the View > CPlane tool to do that one.

But it sounds like saving to AI format would generate the flattened traced curves you need, then you can read that AI file back in to MoI for further processing like deleting or trimming portions of it or whatever.

Does that help with what you need?

Also one other note - you don't need to draw new curves over top of edges, you can extract edges as regular curve objects by selecting the edges (select 1 and then do Ctrl+A to select all of them) and then doing a copy and paste (Ctrl+C then Ctrl+V). Then you will have a bunch of regular curve objects in the same locations of the edges of the solid, and you can hide or delete the solid and then just work on the curves after that.

- Michael

Hi Rado,

> I was hoping that there would be a way to take a
> solid and somehow derive all of the lines that were
> used to create the solid.

When you say: "all of the lines that were used to create the solid", are you talking about the edges of the solid, or something else?

It's possible for solids to be created in several different ways, for example you can just draw a box without actually starting by drawing curves first. So it's not always the case that solids are created by drawing curves initially.

But solids do have edge curves which are part of their structure - if that's what you are talking about then selecting them and doing a Ctrl+C copy followed by a Ctrl+V paste will duplicate the edges as regular curve objects that are separate from the solid.

- Michael

Edge selection on a solid is by "drilldown".. So select the solid, then go to an edge and "select again" will now start to highlight the edges of the solid... Once you have one drilldown edge selected, window selecting will select edges also to get planar groups of edges.. Then the Ctrl+C/V will copy and paste them as new curve objects.

Yeah, sorry if I still wasn't clear. I meant the edges... the selection of one edge then the crtl + A to select all is exactly what I was after!!!!!!!

I'm taking those lines and copying them then bringing them flat into one 2d orientation. Then I can trim as necessary to get the correct perspective view of the section cut.

Thanks so much, this is saving me quite a bit of time!!!!

For making it easier to cut you can try just drawing a line instead of making the whole plane, and for the section i think it will be useful to use the silhouette command with the include edges option turned on that gives you only the lines that you want.

thanks.

Yeah the silhouette command gives me something closer to what I want without giving me all of the lines. It does give me some of the hidden lines from a view still... not sure why but using this saves even more time!

Thanks

Hi Rado, the silhouette command just generates silhouettes only and does not do any hidden line processing itself.

I do want to add in hidden line processing into MoI as well, but it's something that requires some various extra calculations in addition to calculating the silhouette curves.

- Michael

Hi Michael,

I think Rado is saying that the silhouette command doesn't work quiet well on this model and hidden lines are being generated, I was playing around with this also, you'll find a quick model attached to try.

Cheers

Hi Danny,

> I think Rado is saying that the silhouette command doesn't
> work quiet well on this model and hidden lines are being
> generated

Yes, that's what I was trying to describe - silhouette currently will generate all "potential" silhouettes, which for curved surfaces means tracing a curve where the surface normal is perpendicular to the view, and for a joined creased edge (when "Include edges" is enabled) it means an edge that has a surface normal on one side pointing towards the eyepoint and the other surface normal on the other side of the edge points away from the eyepoint.

Later on I want to have some additional methods that will take these potential silhouettes and figure out which pieces of them are hidden and which pieces are visible.

Right now that hidden-line processing is not done, so you get all potential silhouettes generated, including ones that would be hidden.

I can't see anything actually going wrong with the silhouette generation in the model you posted (given the way Silhouette currently works with "potential silhouette" generation as described above), can you maybe point out one particular silhouette line that you think is an error?

- Michael

I see Michael, when you describe how silhouette is working and is missing hidden line 'removal' then it all makes sense.

Cheers

Yeah...

It works better for some cuts than others. This weird off-axis cut for example doesn't give the result you would expect. Reading Michael's description of how the command works, I see now why that's the case.

"Later on I want to have some additional methods that will take these potential silhouettes and figure out which pieces of them are hidden and which pieces are visible."

This would be amazing. Does Rhino currently have something like this? I have access to it at school...

The attached image shows the cut on the right that was performed with the silhouette command (the one on the left is the one I traced and how it should look from this perspective view).

Hi Rado,

> This would be amazing. Does Rhino currently have something like this?

Yes, Rhino has a command called Make2D which will generate a hidden-line drawing of your model. It puts the output as 2D curves that are flat in the Top view.

Rhino also has a silhouette command, but it seems to duplicate every creased edge of a solid no matter if it is a potential silhouette or not.

I may be able to tune up MoI's silhouette generator for edges on solids a bit more by also trying to figure out if an edge is a convex edge of the solid or not, and only allowing it as a potential silhouette if it is.

- Michael

Cool. I'll have to try it at school tomorrow. Thanks for the help!

Other problem with the silhouette command is that you cant make it work with multiple objects, i mean MoI doesnt know if an object is behind other object, it just makes one silhouette for each one.

Hi Ed, yeah right now Silhouette can just give you the sort of "raw materials" of various potential curves to use, particularly on curved surfaces where there may not already be an edge in the model along the silhouette line. But then you need to manually process them to delete and trim out pieces that you want to remove.

- Michael