3101 20th Street — how this model was built

Sources: Studio BBA “CONDUCTOR — 3101 20th Street”, SD Final Pricing Rev 2 (2026-07-14), 17 sheets; Calco Commercial listing brochure (photos, floorplans). APN 4084/001.

Method

Vector extraction, not tracing. The architect's PDF is vector. Every wall line, door swing, glazing panel, stair tread and text label was read from the sheet's drawing operators (PyMuPDF), not digitised from an image.
Scale calibration. Sheets are full-size 36×24 at 1/4" = 1'-0", i.e. 18 pt per foot. Verified against the drawing's own dimension: the open office interior measures 423.5 pt = 23'-6", which matches the 23'-6" dimension string on A2.2.
Registration between floors. Each level is aligned on structural grid 1 (north face) and the east outer face. The grid spacings agree on all three plan sheets to 0.01 pt (232.76, 232.76, 201.23, 231.26, 243.27×4). Sheet A2.1 is stored with a 180° page rotation, so its floor plan and RCP swap places in vector space. This was detected and corrected.
Walls. Wall linework was rasterised at 4 px/inch with the exterior inner faces sealed. Thin enclosed regions (≤ 7½" half-thickness) were classified as wall poché, and their outlines were snapped back to the exact vector coordinates. False positives (fixtures, door leaves, sills, an elevation tag) were removed by hand.
Openings. Exterior window and door jambs come from breaks in the outer-face line on each plan. Door swings were fitted as circles to the arc polylines, giving hinge, leaf width and swing direction.
Heights. Taken from section A4.4 and interior elevations A6.0 / A6.3 at 3/8" = 1'-0" (27 pt/ft).
Check. In the viewer, Drawing overlay draws the original A2.x linework at its true coordinates on each floor, so any deviation is visible.

What is exact vs. estimated

Element	Value	Status
Footprint	103'-11 ½" (grid 1–9) × 24'-10 ⅜"	from drawings
Exterior wall thickness	8"	from drawings
Interior walls, WC blocks, shafts, posts, guards	A2.1–A2.3 poché	from drawings
Window/door positions in plan (all façades)	A2.1–A2.3 (L1 east from L1 RCP)	from drawings
Door hinges, widths, swings	arc fits	from drawings
Level 1 / 2 / 3 floor elevations	1'-3" / 12'-7" / 23'-4"	from drawings
Top of parapet	35'-7"	from drawings
Mezzanine opening (great room)	u 63.91–99.26, v 4.32–20.36 ft	from drawings
L1 east windows	sill 4'-0", head 9'-9" AFF	A6.0
L2 east windows	sill 3'-10", head 9'-0" AFF	A6.3
Kitchen island / back counter, Fish Bowl glazing, gym rubber & turf	coloured fills on A2.1/A2.2	from drawings
Stairs (south stack; north L2→L3)	tread lines + UP/DN on plans	inferred
North stair L1→L2 (lobby run, landing, return)	tread lines on A2.1; janitor “sloped ceiling under stair”	inferred
L3 window and 20th St façade window heights	no elevation in set	from photos
Roof deck	flat at ≈34'-11" (drawn with a slight slope on A4.4)	simplified
“Pipe Organs” gable, cornice, arches, signage, colours	listing photos	from photos
Joists (2×10 @ 16" o.c.), roof cyclone, hatch	RCPs + photos	representative
Furniture	positioned from A2.x furniture layouts	approximate
Streets, neighbours, cars, trees	photos	context only

Coordinates in the viewer

Hovering reads out position as feet south of grid 1 (the 20th St face), feet west of the east face (the Alabama St face), and elevation above the Level 1 datum. The measure tool reports true distances in feet-inches.

Pipeline (re-runnable)

tools/extract.py → tools/walls2.py / export_walls.py → tools/openings.py → tools/build_data.py writes site/data/building.json. The viewer (site/js, Three.js r170, vendored) generates all geometry from that file at load.

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