ACA: Curved Mass Elements - Part 2: Shape Impact

First article in the series: ACA: Curved Mass Elements - Part 1: FacetDev and FacetMax

The Shape property of a curved Mass Element will affect how it reacts to the FacetDev and FacetMax settings. Any of the standard shapes that involve a curve, Arch, Barrel Vault, Cone, Cylinder, Dome, Doric and Sphere, will be initially placed based on the settings of FacetDev and FacetMax, and will update when changes to the FacetDev value would result in a different number of segments. A change to the value of FacetMax will not result in a change to the faceting of existing Mass Elements, even if it would cause a lesser or greater number of segments. The effect of a change to FacetMax on existing objects will be seen only if the value of FacetDev is subsequently changed by an amount sufficient to result in a different number of facets.

Mass Element Extrusions and Revolutions that have curves in the defining Profile will also retain the ability to change the number of facets when FacetDev is changed. Freeform Mass Elements, however, will have the number of facets present at the time of creation, regardless of later changes to the value of FacetDev. How can you end up with a Freeform Mass Element? The following will produce one:

• Use of the Boolean tools to create Unions, Subtractions or Intersections of two or more Mass Elements that results in a shape that cannot be created by extruding a Profile placed in the X-Y plane in which the first object was created.
• Use of the AecMassElementConvert command to convert an AEC object or an AutoCAD 3D Solid to a Mass Element. The Convert to Mass Element tool on the out-of-the-box Massing palette (in the Design tool palette group, in the US Imperial content, and, likely other content as well) runs this command. You can also access this command by selecting an AutoCAD 3D Solid, right clicking and chosing Convert to > Mass Element from the context menu.
• Use of the ConvertMEToFFME command to convert an AutoCAD 3D Solid or a standard-shape Mass Element to a Freeform Mass Element. For standard-shape Mass Elements, this command can be invoked by selecting the Mass Element, right clicking and choosing Convert to > Freeform Mass Element on the context menu. NOTE: If you right click on one of the standard-shape tools on the Massing tool palette, and choose Apply Tool Properties to > Mass Element, the ConvertMEToFFME command will be run, but the 3D Solid or Mass Element will be converted into a Mass Element with the standard shape of the tool which was right-clicked.

In the images below, all three things started from the same source. At the lower left, there are the original objects: a Cylinder base and a Cone on top. In the middle, with FacetDev set to 20, with the Cylinder selected, Boolean > Union was selected from the right-click context menu, and then the Cone was chosen. The same operation was performed on the source objects in the upper right, but with FacetDev set to 0.5. In the top image, FaceDev is set to 0.5, and you can see that the facets on the Freeform Mass Element in the upper right match those of the Cylinder and Cone in the lower left, while the Freeform Mass Element in the middle retains the faceting that was current when it was created. For comparison, FacetDev is set to 20 in the lower image, and you can see that the faceting of the middle Freeform Mass Element matches that of the Cylinder and Cone in the lower left, while the faceting of the Freeform Mass Element in the upper right remains as it was at the time it was created.

ACA: Curved Mass Elements - Part 1: FacetDev and FacetMax

A thread in the AutoCAD^® Architecture Forum last month brought to my attention that I have not yet addressed how AutoCAD Architecture handles "curved" Mass Elements. "Curved" is in quotation marks because AutoCAD Architecture does not display Mass Elements with true curves, but instead will approximate curves with a series of straight-line segments (2D) or facets (3D).

In the image above, a Mass Element Cylinder with a radius of 10'-0" and a height of 5'-0" has been placed, with FacetDev set to 10'-0" to make the facets obvious.

Two settings control the number of segments that are generated, FacetDev and FacetMax:

• FacetDev is the allowable deviation of a facet from the true curve, and represents the maximum distance allowed from the midpoint of a facet, perpendicular to the true curve. Larger values will generate fewer facets. Smaller values will generate more facets. A full circle will never have less than eight segments, as seen in the image above. FacetDev must be a positive (non-zero, non-negative) value. Note: If imperial architectural units are set current, the command line will show the current value as a linear distance in those units (feet and inches), the value you enter needs to be a real number, without any feet or inchese symbols. For example, to set a value of 1'-0", type 12 and press the ENTER key.
• FacetMax sets a maximum number of facets for a single curve. For designs that feature curves with a wide range of radii, FacetMax allows setting FacetDev to a sufficiently small number to achieve a reasonable smoothness on the smaller radii without imposing a serious performance hit due to the large number of segments on the larger radii, which would look smooth with larger FacetDev value. Valid values for FacetMax are integers between 100 and 10000, inclusive.

In the image below, I changed the Visual Style from Conceptual (used in previous image) and I set DISPSILH to 0, so that the lines between facets on the curved surface will show (rather than just displaying the silhouette), viewing the same Mass Element Cylinder as in the previous image. On the left side, FACETDEV remains set to 120 (or 10'-0"). On the right, FACETDEV has been set to 0.5 (or 1/2"). The first value is high enough to result in the minimum 8 facets. The second number results in a much higher number of facets, and is closer to a smooth curve.

With DISPSILH reset back to 1, the image below shows the same cylinder in the 2D Wireframe (left) and Conceptual (right) Visual Styles.

Next article in the series: ACA: Curved Mass Elements - Part 2: Shape Impact