Here's a way to build a truncated icosa from scratch. I'm sure there are other ways! The secret here is to assign a lot of points to the construction circles so that a "true" intersection can be calculated.

build icosa.skp

Thanks for that TIG...all useful tips

Coming from a standard CAD background I always felt frustrated that I couldn't just click LINE>EXTEND. But now I see there are a number of ways to do that!

Yes that's good.

At least we are being protected from the impossible!

Well now I don't feel so bad!

I had already looked through the SU help files but now I look and there it is under Move Tool >> Stretching Geometry

very useful though

Thanks Eric

that's real easy. I've been using SU for a while now and I didn't know that. I probably learned it once and then forgot.

I see it also works with vertices of 2d and 3d objects. And with lines as well. Nice.

Is it possible to move a point/vertex in SU?

For example, to extend a line, one end point could be moved to the new position.

If not, how do you extend a line, without adding another line segment?

Thanks John

I have been experimenting with that and I get it now. The scaling is a useful trick.

Thanks Guys for the input. I have to say this is a great forum!

What I am really trying to do is to model a dome-shaped roof. The geometry is not regular, so I plan to make the basic curve with sandbox tools. Then it will need thickness. So it looks like the copy, scale method will be the one. Bob's system is very clean and economical although the problem still remains to unify the two skins into a single solid object. This is covered by Jean in Scene 6 of his how-to...just by adding a few lines. I guess one might also resort to the method suggested by Masta of intersecting the object with planes and then trimming.

The thing about making a perfect one-eighth-sphere with the follow-me tool is just out of curiosity, but for me it sheds some light on how the tool actually works.

@unknownuser said:

Therefore the last segment will be over-extruded (actually normally following the perpendicular way SU thinks the extrusion should go) and you end up with a crooked top part.

Gaieus, I thinks that sums it up.

PS I didn't follow your explanation about the hole in Gidons picture and scaling up.

I've been playing around with Gidon's method and it seems like the follow me tool produces some strange results. In Gidon's diagram you can see that the shape has a "V" cut out of it at the top. This generally seems to be the case. In fact I would be interested to know if it is possible to make a perfect one-eighth-sphere (solid or hollow) using just the follow me tool.

It seems like your method is the way to get a precise result, Gaieus. And also, it looks like the best way also to give thickness to complex curves, like as you say boat hulls.

It can be done as you say by copying, scaling and repositioning, but it is quite fiddly!

Is there a smart way to add thicknessto a curved surface, say a hemisphere...in other words to create a hemispherical shell with thickness. The push/pull tool only seems to work on plane surfaces.

I can see that such a shell could be made from scratch as an object of rotation, but...what if one already had (for example) a hemispherical surface of zero thickness?

Thanks for that info Anssi.

I had a look inside the dxf file in question and it doesn't even have a XDATA section. So I guess that answers the question!

Getting back to the original question, I've discovered two things.

dxf seems to be a very basic format which has not been developed much recently. It handles geometry very well. It only handles color in the sense of "pen color", ie the color of the pen used in a cad sense, and not in the sense of a "material". So this is not much use since SU doesn't use different pen colors.

When SU imports a dxf (from Cycas anyway) it seems to create a new layer structure based on the materials assigned in Cycas, and not based on the original layer structure within Cycas which is usually based on architectural features. This is interesting and weird but still useful when it comes to reassigning materials to the objects within SU, because one layer can be turned on at a time and the material assigned to all visible objects.

(Still haven't quite got my head around the way layers work in SU...Layer 0 seems mysterious...leave that for another day!)

Any comments?

Hi Gaieus and Jon,

It seems like the dxf exports from Cycas don't contain any color or material info. I tried importing said dxfs into as many apps as I could think of than open dxfs (Quick3d, Alteros, ctrlview, amapi, blender) and none of them showed any color. Not too serious I suppose, because the layer structure is preserved, so that makes assigning materials in SU much easier.

Jon and Edson,

Cycas is a most excellent package. I have been using it for a year now as my main architectural tool, maybe 5 to 8 hours a day. It was original written for Linux, but the windows version is also super stable and totally reliable.

As you say Jon the interface and in fact the whole feel of it is very different from any other cad software...it really is fresh thinking. Because it is just as easy to draw a 3d wall as it is to draw a line, it almost entirely eliminates the need for any constructional 2d drawing (of course straight 2d drafting is fully supported). Windows, doors in 3d are a sinch. Roofs, columns, beams, any arch features can be constructed.

As a solid modeller it has a lot of scope, but limitations as well. It's strength lies in its simplicity, and the ease with which one can create a 3d architectural model and then from that
produce high quality photo renderings AND fully annotated and dimensioned technical drawings on paper in all standard views as well as custom perspective views.

Forgive me I could go on!

Probably been asked before...I've started importing architectural models into SU in dxf format.
They are multilayer models created in Cycas and all objects have a material/texture assigned.

I export them from Cycas as dxf and then import them into SU. All objects appear in SU with the default material. I'm wondering at what stage the material/texture information is lost.

Am I bound to reassign materials again form within SU or is there a smarter way? Would appreciate any input on this.

Thanks Jean, that's good as a workaround. I liked the method with the vertical cutting planes.

Just for interest, here is another method that may be useful but doesn't work in all situations.
alternative partial lathe

Does anyone know of a Ruby script for a lathe tool? There is one (by Frank Wieser, 2004) which looks like it should do the job, but I couldn't get much out of it it SU6.

What I need to do it to produce lathed objects (solids of rotation) where the angle of rotation is less than 360 deg.

The follow me tool produces undesirable results when the angle is less than 360. I know it is possible to produce a polar array of a polyline around an axis (using the rotate tool) and then use sandbox contours to skin the lines. But a simple rotate function would be better.