I have a problem with creating a dome out of a curtain wall

[Anonymous]

I tried to create a dome following the instructions of this fellow :

https://www.youtube.com/watch?v=W6dBhuw3_RE

But I have trouble when I try to shape the curtain wall to the regular wall as he does. That step is at about 3:50 into the video.

I cannot snap the nodes to the wall as he does. The nodes, as I move them, act as there is no wall at all. I can only place them approximately, which is, obviously, not precise enough.

I hope I explained it good enough. If not, please tell me to elaborate more.

I'm using ArchiCAD 18 and the person in the video is using ArchiCAD 15

Thank you in advance,
Dušan

[Laszlo Nagy]

If you watch closely in the video, he moves the cursor along the Grid of the Curtain Wall. At the intersection point of the grid and the inner surface of the Wall, the shape of the cursor changes to an Arrow with Intersection shape. Try to stop the video if it is not easy for you to see because he stops only for a very short time.
But basically the cursor shape change gives you the clue that a special point has been found, in this instance the intersection point of the grid line and a Wall surface.

[Anonymous]

First, thank you for the reply!

Now, the problem is exactly that. My cursor does not change at that point. I know it should change, as you say, at the intersection of the grid and walls inner surface, but it doesn't. The cursor acts as if there is no wall at all. That is exactly my problem, and I cannot figure out why it is behaving like that.

Now, I set those points approximately where the intersection is, and made the dome that way. But it really bothers me that I can't do it precisely at the intersection.

I hope I managed to explain my problem more clearly.

[Laszlo Nagy]

I have checked this in both AC15 and AC18.
You are right, the cursor shape change works in AC15 but not in AC18.
In AC15 the cursor shape changes to the "Arrow with Intersection" shape when it finds the intersection point of the Curtain Wall boundary polygon and a Curtain Wall grid line, or the intersection point of a Curtain Wall grid line and the Wall surface.
In AC18 this doesn't work. It seems like this functionality got lost somewhere along the way.
I will report this to Graphisoft as a bug.

[Laszlo Nagy]

I was thinking what the workaround for this problem could be.
Here is one idea: try to model the points you need on the inside surfaces of the Wall you need to snap to for the Curtain Wall boundary.
One way to do it is with the Morph Tool's Polygonal method, suing which you will be able to create a 3D polygon and the cursor will be able to sense the nodes of this 3D polygon.
So maybe create a Zero-Depth Section Line that is on the inner side of either Wall, and the Section facing the other Wall (so you will see the Curtain Wall in the Section).
Then use the Polygonal Method of the Morph Tool to draw the segments over the intersection lines of the Curtain Wall and the vertical Section plane you now see in the section.
Then you will be able to use this Morph polygon in 3D for the editing of the Curtain Wall boundary. For me the cursor properly changes shape at the intersection points of the Morph polygon and the Curtain Wall grid lines (when Scheme is made visible).