Every August I walk the same county fairgrounds: a half-mile dirt track, a white grandstand, and fourteen livestock barns that all look alike until you need to tell them apart. This spring the county asked whether two barns could be replaced and a new exhibition hall added without moving the track.
I built the model as a pipeline instead of a one-off scene. The goal was simple: change one input, rebuild the whole thing, and get the same result twice.
What the model has to answer
Three questions drove the work:
• Can a new exhibition hall fit without blocking the grandstand sightlines?
• Which barns are worth keeping, and which are past repair?
• How does a new hall change drainage and truck access on the gravel lanes?
Every step exists to answer one of those.
Ground and lanes first
OpenRoads handled the existing conditions. I traced the track centerline, the gravel lanes, and the parking edges from aerial imagery, then built a terrain surface from the county contours. The site is flatter than it looks, but the infield drains toward the south gate.
I exported the surface and lane alignments in feet. That became the fixed base; no other tool invented its own ground.
Rules for buildings that repeat
CityEngine did the repetitive work. The fourteen barns fall into three types: a long open-front shed, a smaller enclosed barn, and a two-story show barn. I measured each type from photos and wrote a CGA rule for it, with parameters for length, bay count, and roof pitch.
The payoff was speed: once the rules existed, I could place all fourteen barns in an afternoon and regenerate the row when a dimension changed. The grandstand got its own rule because its stepped concrete cannot be approximated with a box.
Fill the gap with a box
The exhibition hall was the unknown. I used GenAnywhere and drew a box over the overflow parking east of the track, set a height of 28 feet, and let the tool generate massing inside the box. The principle is straightforward: outline an area on the map, and the AI fills it with building volumes. You are testing occupancy, not designing a facade.
The first box crossed the track fence by 12 feet. The second pulled the west edge back and produced a long hall with a service yard.
Compare the hall options
Archshaper generated three massing schemes from the box: a long gable, a T-shaped plan, and a two-story block. I cared about two things: the view from the top of the grandstand, and whether a truck could turn around at the loading door.
The long gable won. It kept the sightline, gave the service yard a straight pull-through, and left room for a future second phase. The two-story block looked efficient on paper but threw a shadow across the warm-up ring in the late afternoon.
Props from the barn row
Meshy handled the small assets. I took photos of a cupola, a sliding barn door, and a section of grandstand railing, and converted each into a textured mesh. The originals were too heavy for a site model, so I decimated them and kept one material per asset.
The cupolas matter more than they should. Fourteen identical roofs look like a diagram. Fourteen roofs with slightly different cupola positions look like a place.
The manifest
Every export is listed in a small manifest: file name, units, coordinate reference, level of detail, rule version, and a hash. The manifest is boring, and that is the point. When a rule changes, the hash changes, and I know which views need a second look.
The rebuild test deletes the generated scene, reruns the pipeline from the manifest, and compares object counts and bounding boxes. The last run took six minutes and matched exactly. That is the only proof a pipeline is repeatable.
What broke
The first failure was units. CityEngine was set to meters while OpenRoads exported feet, so every barn came in at a third of its real length. The manifest now records units for each step.
The second was weight. The first Meshy assets were beautiful and unusable at site scale. Decimation fixed it.
Why this site works as a test
Fairgrounds are repetitive, which makes them a good stress test. They also have one irreplaceable thing, the track, which forces every new building to prove it belongs. The pipeline narrowed the conversation to two schemes and showed which one the site could absorb.
That is enough for a county meeting.
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