Tuesday, September 29, 2015

2. Generating nodes. Designing curved architectural surfaces using Revit, Part 2.

Generating nodes

To make a surface buildable, it must be broken into sections and a system for fabrication devised. After creating a surface, the surface must be subdivided into nodes. Nodes are very important; they control how elements are repeated across a surface using parametric variation. A node defines the unique tangent plane at that point on the surface and the unique surface normal. It carries with it a coordinate system and rotation of its xy axes (the local z axis is the surface normal).

Revit provides three ways of making points on a surface: divided surfaces (with patterns), intersects, and hosted points.

Before doing this part, you will need a surface. If you don’t have a surface, the previous post describes how to make a surface for testing and experimenting.

The divided surfaces are very easy to use. Simply select the surface and pick the Divide surface button. It may be necessary to tap the Tab key to get Revit to select the surface rather than a line.

A divided surface is a complex element. First, the Type selector allows one to pick many different types of patterns, including rectangles, triangles, brick patters, hexagons, and others. Second, the Surface Representation panel extension allows one to control what is displayed. Use it to turn on the nodes representation.

You can control the number of nodes on the U Grid and the V grid. You can rotate the grid and offset it from the edge. The Layout option allows one to control the spacing between nodes to be either a set dimension or equidistant (fixed number).

A second way of making nodes is to use intersects. An intersect is a reference plane that the user establishes. The divided surface uses its own logic to create nodes. Often it defines nodes equidistant apart. On a curved surface, this may not align with a grid line in plan view. Since architects generally establish a grid for columns, alignment with the grid is important. Intersects enable one to force that alignment.

To see the nodes created with intersects, set the divided surface to have only 1 space on its U grid and 1 space on the V grid. These will be along the edge of the surface.

Use the Intersects tool and select reference planes to intersect the surface. Reference planes must also intersect each other to define a unique point on the surface. Use the check icon to finish your selection. Turn nodes on to make sure that you can see the results.

The final method (that I have discovered) for finding points on a surface that can be used in designing a structural system is to use a line that intersects the surface. This gives you complete and total control of the points used for structural support. However, it requires much more work. To experiment with this, draw a vertical line through the surface.

An easy way to draw the intersecting vertical line is to switch the work plane to be one of the vertical planes that is midway along the surface. Draw the vertical line.

Use the Point tool and draw a point on the vertical line. Make sure that the Host on Face icon is active rather than the Host on Work Plane. If done correctly, when you move the line the point will move with it.

Now select the point. A new option appears to Host Point By Intersection. Choose this option and then select the surface.

There is now a point at the intersection of the line and the surface. If the shape of the surface changes or the location of the line changes, the location of the point will change. Trying moving the line around to see this behavior.

Once you have created nodes on the surface, it is possible to start applying adaptive components to place themselves on the surface and adapt their dimensions and geometry. 

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