With the Grasshopper - ARCHICAD Connection tool, you can enhance your BIM model with complicated shapes that can not be defined easily by with the default ARCHICAD tools. In order to be able to properly represent and document these shapes, while keeping the geometry and BIM information intact and the speed unaffected, we developed the Grasshopper Loft Object. This article explains what this tool is capable of, and how to use it.
You can get the object from BIMcomponents.com, or you can search for them in the Object Tool Settings dialog Search bar, and download them directly into the embedded library.
This object is designed to be used through the Grasshopper - ARCHICAD connection tool. This means that to use it you will need to be familiar with Grasshopper, and there are several settings in the object that cannot be set in ARCHICAD.
The resulting object will be highly parametric: you can control the Building Material, Hotspot visibility, Level of Detail, Visibility of edges, etc.; and it also allows you to control the floor plan representation, which responds to cut plane settings.
Similarly to the Loft command in Rhino, this object takes different cross-sections as an input, and connects them to form a continuous surface or body. These cross-sections can be in any angle in the 3D space, but they should have the same amount of points, properly aligned. This can either be achieved by setting up the sections in grasshopper to begin with, or if you already have a shape modelled, it can be sliced in Grasshopper to generate these cross-sections.
Most settings can be controlled through Grasshopper as well, but there are two parameters that are only available through the Object Settings Grasshopper Component:
The rest of the settings are to control the 2D and 3D representation of the Object. Most of these are standard to other ARCHICAD elements, but there are several settings that are specific to this object:
Let's see how to translate your Model to be able to use it with the Grasshopper Loft Object. In this example we will translate a tube that changes its cross-section from one end to another. You can download the .GH file used in this example from here.
When your cross-sections are polygonal, it is easy to turn them into a set of 3D points, because you just have to deconstruct them into their vertices. With curved cross-sections things are a bit more complicated. Here are a few things you should keep in mind:
If you are not generating the cross-sections from scratch inside Grasshopper, but slicing an existing geometry, you might distribute planes along a curve to slice the shape with. In this case make sure that the first and last segments of the curves are perfectly perpendicular to the start and end faces/sections, otherwise they might slice them in an angle, and end up with a different (wrong) starting section.
It is easy to create a shape going along a path, that is parallel with itself at some points (the most simple example is a path shaped like a U). In such situations, cutting planes/frames can cut through 2 parts of the shape at once, creating faulty sections. You can use the Rectangle/Plane Surface Components to limit your cutting plane size.
If you are slicing a shape that is capped with a surface on the beginning and the end, the first and last planes will not generate the section from the tube, but from the parallel plane. This plane can have a different point order, so in this case your first and last sections might end up distorted. To avoid this, delete these capping surfaces before slicing the shape.