What Sun Path does

Drops your Rhino model under a sky dome and traces the sun across any date or time, showing shadows on the building and on the ground. Useful for shading studies and seasonal comparisons.

Input:

.3dm + .epw

Output:

3D / 2D sun path

Modes:

Single · Seasonal · Multi-day · Sun hours

How it works

Sun position is the same NOAA/Meeus algorithm the professional tools use, checked against NREL's reference implementation rather than asserted. Sun hours are computed by projecting geometry onto the ground and facade grids, which was proven cell-for-cell identical to an independent brute-force ray-cast — so the shadows are not an approximation of the method, they are the method.

• NOAA/Meeus solar-position algorithm — the same family as Ladybug and Radiance's sunpath.
• Validated against NREL SPA (Reda & Andreas, NREL/TP-560-34302) via pvlib: worst altitude error 0.005°, worst azimuth error 0.022° across the test set.
• Sun hours: per-sample geometry projection onto the grid with per-sample dedup — equivalent to a ray test at every cell centre, and verified cell-exact against a Möller–Trumbore ray-cast reference (zero mismatching cells).
• Ground grid and facade grid share one sun-sample list, so the two overlays can never disagree.
• Integer-minute day loop at 6 / 10 / 30 min (single day) or 0.5 / 1 / 2 h (multi-day windows), end-exclusive.
• Shadow outlines vectorise to SVG, DXF and Rhino via marching squares.

How to use it

1. Load a weather file. Sun position depends on latitude/longitude — load an EPW first.
2. Upload your model. A .3dm (or .obj / .fbx) of your massing + context.
3. Pick an analysis mode. Single date, solstice comparison, or a custom multi-day range.
4. Move the sun. Drag the date/time sliders to find your critical moments.
5. Map sun hours. Optional: compute direct-sun hours per point over a date window as a ground heatmap, exportable to SVG / DXF / Rhino. Pick building layers to color their facades too.
6. Animate or export. Play the full year, or export a video for presentations.

Best used for

• Shading and overshadowing studies on a representative day (equinox, solstices).
• Finding the worst-case moment before committing to a shading device or facade.
• Amenity sun-access screening against the usual thresholds — BRE 209 (2 h on 50% of area, 21 March), BS EN 17037 (1.5 / 3 / 4 h), DIN 5034-1.
• Getting shadow outlines out to CAD as real geometry for a drawing.

Not a substitute for

• A planning-submission overshadowing report — that needs a stamped study.
• Interior daylight levels or glare (use the Daylight tool).
• Sun-hours certification of any kind.

Known limits

• Sun-up cutoff is 0.5° geometric altitude, not the −0.833° refracted horizon the NOAA calculator uses, so day lengths read about 0.3–0.4 h shorter at London latitudes. Stated rather than hidden: beam that low is blocked by real horizons the model does not have.
• A 1-hour window underestimates sun hours by roughly 3% against 5-minute stepping (Brembilla et al., BS2021) — drop to 6 or 10 minutes when the number matters, not just the picture.
• The sun is treated as a point, so shadow edges are hard — there is no penumbra.
• Only geometry you load casts shadows. Miss out the neighbours and the result is optimistic.
• Ground grid defaults to 1.5 m cells; fine detail below that resolution is not resolved.

Read the full Sun Path guide →