I needed a quick 3D blockout of the San Francisco–Oakland Bay Bridge for a lighting and camera test. Hand-modeling 4.5 miles of bridge was out of the question. I wanted something rough enough to answer scale questions in an afternoon, not a survey asset.
So I tried a map-first approach: select the area, generate a model, then fix what the generator cannot know.
TL;DR
- A selection covering both spans and the island produced a usable massing model in minutes.
- Scale was close enough for camera blocking, not for measurement.
- Cables and tunnel portals needed manual work.
- Good for silhouette and fog tests, bad for structural detail. ## The actual constraint This was previsualization. I wanted cameras at deck level, tower base, and on a hillside, then to see how fog separated the layers. I needed the footprint, deck heights, tower positions, and a rough city backdrop. Not rivets or lane markings. That distinction matters. A model that is wrong about a bolt can still be right about a silhouette. A model that is wrong about deck height cannot. ## Step 1: define the selection I used GenAnywhere, which works by drawing an area on a map and generating a 3D model from that selection. My first selection was too tight, just deck and towers, and the result floated in empty space. The second included the corridor from the San Francisco anchorage to the Oakland touchdown, open water on both sides, Yerba Buena Island, and a thin strip of waterfront. That produced a much better base. The selection is the most important input: too small and the model has no context; too large and you spend an hour deleting buildings you do not need. ## Step 2: generate, then audit scale The first export looked convincing until I put a camera at deck level. The eastern tower read too short relative to the roadway. I checked known dimensions, roughly 160 meters for the tower and 624 meters for the main span, and scaled the tower group. After that, proportions matched well enough for blocking. I also counted the towers. The western span has two; the eastern span has one. A quick count catches more errors than it should. ## Step 3: repair the geometry The generator gave me a massing model, not an engineer's model. Three fixes took most of the time:
- Cables. The eastern span's fan came in as straight segments. I replaced it with curves and a radial array, then adjusted the anchor points.
- Suspenders. The western span needed vertical ropes at regular intervals. An array modifier handled it.
- Tunnel portals. The entrances were merged into the terrain. I cut two openings and added simple concrete surrounds. None of this is hard, but it is not automatic. Budget for it.
Step 4: block the cameras
I set three: bay trail at eye level, under the western span looking up at the truss, and East Bay hills with a long lens. The hillside shot immediately showed a problem: the model's city blocks were too tall and blocked the bridge. I scaled the backdrop down and moved the camera.
That is the point of a blockout. You find composition problems before materials.
Where it earns its place
Fast coverage of a large, complex site. Useful silhouettes for fog and lighting tests. Easy iteration on the selection. Enough context to judge how the bridge sits in the bay.
Where it falls apart
Cable topology is approximate, especially on the self-anchored suspension span. Textures are flat at close range. Railings and road markings are missing. Nothing here is suitable for structural analysis, clearance checks, or construction documents.
I would not hand this to an engineer. I would hand it to a layout artist.
When not to use it
If you need measured accuracy, use survey data, CAD, or photogrammetry. If you need a hero close-up of a cable band, model it by hand. The map-first workflow is for the wide shot, the camera plan, and the early look-development pass.
What I would change next time
Split the selection into two runs: eastern span, then western span plus island. Each half had different geometry problems, and fixing them together was messy. Two smaller models joined in Blender would have been faster.
The blockout took an afternoon. Most of that was cable repair, not generation. Fair trade for a scene I would otherwise have skipped.
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