by Dušan Cvetković
Dušan Cvetković
Published November 16, 2021

Subdivision surface modeling, also known as SubD, is an incredibly useful technique for quickly creating smooth and complex architectural geometry in Rhino. In this tutorial, we’ll explore how SubD can be leveraged to efficiently model the famous Diller Scofidio pedestrian bridge in Colorado Springs.

Overview of the SubD Speed Modeling Process

SubD speed modeling involves starting with a simple polygon mesh and iteratively subdividing and smoothing it to create a higher-resolution surface. The key steps are:

  • Set up reference images and views
  • Create an initial low-poly mesh
  • Subdivide and smooth to add detail
  • Refine shape and topology
  • Add supporting edge loops and creases
  • Bridge and connect pieces
  • Mirror the geometry

Setting Up the Base Mesh

We begin by analyzing reference images to understand the overall shape and topology of the bridge design. After setting up front and side view image planes, a mirror plane is created to take advantage of the bridge's symmetry.

Initial mesh polygons are constructed to match the front elevation using four-edged planar surfaces. The mesh is iteratively refined by subdividing edges and moving vertices to match the reference.

Supporting edges are added around openings and details.The overall form is shaped to match the side view by scaling and moving control points. Surfaces are trimmed and extended to create void spaces.

Refining the Mesh and Adding Details

With the basic form roughed out, we can refine the shape and add supporting edge loops. The goal is to end up with quads as much as possible, with clean topology and hard edges in the correct spots.

The circular underside of the bridge is modeled by revolving and trimming a curved rail profile surface. The ends are sealed up and rounded out using filled surfaces.

Small details like the fins and ridges along the top are added in at this stage by inserting and connecting additional edges. A separate bridging element is created to connect the two sides.

Mirroring and Connecting the Pieces

To complete the SubD speed modeling process, the half-bridge mesh is mirrored across the center plane. Rather than keeping them separate, the two sides are then bridged and joined into a single mesh.

The base surfaces are constructed using a combination of swept and revolved profiles. Balustrade panels and fence elements are made by splitting, copying, and extruding faces of a subdivided surface.

The curved substrate for the net is produced by trimming and patching a thin surface section to the rails. This is later exported to Grasshopper where the net pattern is generated.

SubD Speeds Up Architectural Modeling

As we’ve seen, SubD techniques allow fast iteration and experimentation when modeling complex shapes like the Diller Scofidio bridge. By leveraging subdivision modeling in Rhino, impressive architectural models can be produced efficiently.

The ability to smoothly refine geometry on the fly makes SubD modeling ideal for quickly mocking up designs based on reference images. The localized control over edges also helps recreate specific shapes and details.

Subdivision surfaces allow you to focus on overall form rather than getting bogged down in complex surface modeling right away. The iterative nature of SubD modeling gives increased flexibility throughout the process.

So next time you need to model an architectural concept or form, consider taking advantage of SubD techniques for a quick and smooth workflow.

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About the Author

Dušan Cvetković is a professional architect from Serbia with international experience in the industry. Collaborated with numerous clients all around the world in the field of architecture design, 3D modeling and software education. He's been teaching Rhinoceros3D to thousands of architects through How to Rhino community and various social media channels.