What Sky Mask does

Stands at a chosen point in your model and measures how much of the sky dome is visible (sky view factor), plus how many hours per year that point sees direct sun. Core daylighting and outdoor comfort metric.

Input:

.3dm + point

Output:

SVF · Shadow autonomy

Sky models:

CIE / Uniform / Clear

How it works

The sky over the sample point is sampled and each direction is tested against your geometry. Two sky view factors come out of the same pass — a purely geometric one, and one weighted by overcast-sky luminance — because the honest answer to how much sky depends on whether you mean area or light.

• The whole sky hemisphere is sampled from the point you pick.
• Geometric SVF: unobstructed patch area as a percentage, uniform sky assumed.
• Weighted SVF: the same patches weighted by CIE overcast luminance, which is brighter at the zenith — so an overhang costs more than a distant wall.
• Direct-sun hours evaluated per date against the same geometry, using the validated sun-position routine shared with Sun Path.
• Shadow autonomy: the share of annual daylight hours the point spends out of direct sun, reported for winter and for the year.
• Fisheye view drawn by stereographic projection, the same convention as a hemispherical photo.

How to use it

1. Upload your model. A .3dm with the building and any context (walls, trees, neighbours).
2. Load weather data. An EPW gives you real annual sunlight hours.
3. Pick an analysis point. Double-click in the 3D view or type X/Y/Z coordinates.
4. Choose a sky model. CIE Overcast for worst-case daylight; Clear for sunshine analysis.
5. Set density. Higher = more accurate, slower.
6. Read the metrics. Diffuse visibility, geometric SVF, shadow autonomy, sunlight hours.

Best used for

• Checking sky access at a courtyard, balcony or window head before the massing is fixed.
• Street-canyon and density studies where the question is how enclosed a space feels.
• Comparing urban design options by sky access at the same point.
• Sanity-checking a daylight result: low SVF explains a dark room.

Not a substitute for

• Interior illuminance or daylight-factor compliance (use the Daylight tool).
• Rights-of-light or planning daylight assessments.
• Thermal comfort on its own — sky access is one input among several.

Known limits

• One point at a time. A point is not a room, and moving it a metre can change the answer materially.
• Only loaded geometry obstructs the sky; trees, canopies and unmodelled neighbours are invisible to it.
• Surfaces are opaque — a louvre or pergola modelled as a solid reads as a solid.
• The weighted SVF assumes a CIE overcast sky, which is the conservative case and not your actual climate.
• Patch resolution is the resolution of the answer: a thin mast may fall between rays.

Read the full Sky Mask guide →