On Land

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At Rill Architects we run ArchiCAD on Mac OS X. If you work at Rill, this is your stuff. If you don't, but you work in ArchiCAD, you may find something interesting. Anybody else, I don't know.
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Somebody asked why the flue object can't show a thickness for the flue liner itself.

Flue on Nothing
One reason: The flue sits atop, and lines up with, the top of the smoke chamber object. In section this gives a continuous void. If a thickness is built in to the flue, there would be a discontinuity at the top of the smoke chamber, and the flue would appear to be supported by nothing. Building the flue thickness should help make a better detail, yet this is worse. I could partly solve this by narrowing the top of the smoke chamber, but that doesn't help with the other, bigger, reason.

The other reason: The flue is designed with SEOs in mind. You have to use it as a subtraction operator, or there's no point. It is a simple solid tube (EXTRUDE, actually) which we use to make a simple void. If the flue wall has a thickness, it becomes a solid ring with nothing in the middle.

Flue Filled
When you subtract with a ring, you get a ring-shaped void, with solid, un-subtracted material in the middle. If you cut a section through such a thing, you'll get masonry fill with two stripes of flue-wall fill going through it, and no void.

Flue Air Fake Air
To fix that, I could simulate emptiness within the flue by filling it with solid stuff with a clear section fill. In order to see this stuff and the wall thickness, we would need to make the flue's layer solid instead of wireframe. The problem there is that in a marqueed 3D view, there would be no void.

Well, I could wireframe the layer in building section combinations and make it solid in wall section, and I could make the thickness option scale sensitive in the flue and the smoke chamber, but we're into serious inelegance now. It's a void, except when it's not and it's simulating a void, and it's scale- and layer combination-dependent, and do I 'really' subtract it to 'simulate' a void, I can't remember.

Once again we have met a limit in GDL object technology where the simplest solution is for Graphisoft to give us more power. There is a directive, MODEL, which allows you to build shapes in wireframe or surfaces-only mode in addition to the default, normal, solid mode. MODEL WIRE makes a wireframe shape that looks exactly like switching a layer to wireframe. MODEL SURFACE makes a shape that looks normal from the outside but is hollow. This sounds promising for our problem until we realize that only MODEL SOLID shapes can act as SEO operators.

Therefore, I want a new MODEL option which will make shapes wireframe, but which will allow the shapes to act as operators. So the flue wall would subtract, and the void within the flue would subtract, but the void would still be a void. My first stab at a name is MODEL OPERATOR, but I'm open to suggestions.