How to create custom Solid bodies using Shell

by lnagy and GRAPHISOFT · updated: 10.04.2012

The Shell Tool that was introduced in ArchiCAD 15 is a very versatile Tool. However, as its name implies, it is a Shell, it is a body of constant thickness generated onto a membrane.

ArchiCAD users may encounter situations where they need the Shell to be a solid body instead of an element of constant thickness. There is a trick you can use to achieve this. It involved using the Trim elements to Roof/Shell command. The following example describes how to do it.

The vertical pieces in this scenario were modeled using complex Columns, we have no problem there creating solid bodies. However, the curved piece could only be modeled using the Shell Tool. The Shell is not solid. How can we make it solid?

In order to achieve this, we use some creative thinking. We will model a Wall piece and will trim this Wall to the Shell.


2.PNG Step 1

Create a Wall large enough so that when trimmed by the Shell it will give us the geometry we want.


3.PNG Step 2

Select the Shell that will trim the Wall, go to the Model panel of its Settings Dialog and set the Trimming Body field to the Editable option. Then click OK to leave the Dialog.

This is important as the Trimming Body is what is considered and used in Trim elements to Roof/Shell operations. When the Trimming Body is set to Upward Extrusion or Downward Extrusion, the Trimming Body is a half-infinite extrusion body in the upward or downward direction, respectively, and will not give us the desired result. With the Editable option the Trimming Body is a finite body located within the boundaries of the actual Shell body.

Note: You can make the Trimming Body of Roofs/Shells visible with the View\On-Screen View Options\Trimming Bodies menu command.


4.PNG Step 3

Select the Wall, and activate the Connect > Trim Elements to Roof/Shell command of the context menu.


5.PNG Step 4

Select the curved Shell piece as the trimming element. The cursor will switch to the House with Dark Roof cursor shape when the Shell is found.


6.PNG Step 5

Move your cursor so that it finds the inside of the Shell.

The blue pre-selection highlight will give you feedback on which part of the Wall will be kept if you click the mouse. Alternately, you can hold down the CTRL (Windows) / CMD (Mac) key which will enter trim mode as shown by the Hatchet cursor shape in the following image. In that case you specify the part of the Wall to be removed.

It is important to note that regardless of which method you use the pre-selection highlight will always show the part that will remain after the trim operation. In this image we can see the cursor is located on the outside part of the Wall (that part of the Wall that falls outside the Trimming Body of the Shell), the shape of the cursor is a Hatchet (so the outside portion will be removed, not kept) and the pre-selection highlight is on the inner portion of the Wall as that portion will be kept under these conditions.


7.PNG Step 6

Click to trim the Wall to the Shell. We now have a Wall that is trimmed by the Shell.

It is easier to understand how and why this is the result if we know that in such a scenario the Trimming Body of the Shell acts as a SEO operator on the Wall (the target element). If we choose the inside of the Wall to remain, the Trimming Body of the Shell performs an Intersection Solid Element Operation on the Wall. If you choose the outside portion of the Wall, the Trimming Body of the Shell PLUS the actual body of the Shell together perform a Subtraction Solid Element Operation on the Wall. So here we have seen an Intersection SEO between the Trimming Body of the Shell and the Wall.

Note: Make sure to create the Shell in such a way that its body grows toward the outside of its membrane defined by its Profile Polygon. This way the Profile Polygon will define the shape you wish to achieve and you will not have to take the thickness of the Shell into consideration. If the Shell body currently grows toward the inside of the Profile Polygon, simply click the Flip button in the Info Box with the Shell selected to flip it to the other side of the Profile Polygon.


8.PNG Step 7

Place the Shell onto a different layer and hide the Layer. This way only the cut Wall bodies will remain visible.

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