uds-simulation

name	uds-simulation
description	Use Ultra Dynamic Sky's real-world astronomical simulation — Simulate Real Sun, Simulate Real Moon, Simulate Real Stars; latitude/longitude/time zone setup; North Yaw; daylight savings; city presets; the simulation date; Simulation Speed; and Use System Time (sync with the OS clock). Use any time the user mentions real-world sun position, latitude/longitude, city presets, accurate sunrise/sunset times for a real location, real star map, real moon phases matching a date, North direction in the level, daylight savings handling, or syncing in-game time to the player's actual system clock.
metadata	{"asset":"Ultra Dynamic Sky (marketplace)","category":"simulation","source-docs":"https://www.ultradynamicsky.com/Documentation/V9/9-5"}

UDS astronomical simulation

UDS can position the sun, moon, and stars using real-world coordinates and dates instead of the simple yaw/pitch/offset settings. Three independent toggles + a location/date block + an OS-clock sync. All settings live in the Simulation category.

Toggle	Overrides	Notes
Simulate Real Sun	Sun Yaw / Pitch / Vertical Offset	Manually Position Sun Target still takes priority
Simulate Real Moon	Moon Yaw / Pitch / Vertical Offset / Moon Phase	Phase is driven by simulated date
Simulate Real Stars	Default tiling stars texture → 360° star map	Both textures exposed in Stars category

When to use this skill

• Need sunrise/sunset times accurate for a real location and date.
• Setting the sky for a specific city — Tokyo at noon on Aug 3rd, etc.
• Star positions matching real constellations.
• Moon phases matching a real date.
• Time of Day should reflect the player's actual wall-clock time.
• Defining what "north" means in the level (level rotation vs world rotation).

Location setup

Setting	Notes
Latitude	Degrees N/S
Longitude	Degrees E/W
Time Zone	UTC offset. Critical — wrong time zone offsets sun position by hours, because Time of Day is interpreted as local time at this location.
North Yaw	What world-space direction = north. Default: north is +X. Degrees, clockwise.

City presets

A city preset applies latitude, longitude, time zone, and daylight savings in one step. The fastest path for "set the sky correctly for City X."

Date

Setting	Effect
Year, Month, Day	Simulation date
Date auto-increment	At runtime, increments forward every night at midnight

For setting date from code, Set Date and Time and Get Date Time handle Date Time structs — see uds-time.

Time speed with simulation on

When Simulate Real Sun is on, Day Length and Night Length are ignored. Instead:

Variable	Meaning
Simulation Speed	Scales runtime time progression. 1 = roughly real time (one real day per one real day)

Daylight savings time

DST options in the Simulation category. When enabled, Time of Day is interpreted with DST applied within the DST start/end times set in the advanced dropdown of the Simulation category.

Use System Time

Use System Time (Simulation category) sets Time of Day and date values from the system clock's UTC time, offset by Time Zone.

This works without enabling the rest of the simulation features — you can use it solely to keep in-game time matching the player's wall clock, without simulating real sun positions.

Simulation accuracy

The complete astronomical algorithms are too expensive in blueprint math, so UDS uses approximations.

Body	Typical accuracy	Caveat
Sun	Within fractions of a degree; worst case ~1° off	Leaves out Earth orbit eccentricity, Earth shape irregularity. Sufficient for almost all practical applications.
Moon	Calibrated using moon's position in 2017	Generally accurate for dates within several decades. Moon appears in correct constellation with correct phase.

If you find edge cases where deviation is worse, that's expected — it's an approximation.

Interaction with other features

Other system	Interaction
Manually Position Sun/Moon Target	Takes priority over simulation
Dusk Time / Dawn Time (Basic Controls)	Ignored when Simulate Real Sun is on — simulation determines horizon-crossing times
Animate Time of Day	Still works — uses Simulation Speed instead of Day Length / Night Length

Runtime / Blueprint control

The simulation toggles, location, date, and DST are mostly static properties. After runtime changes, call Static Properties - Simulation (or Hard Reset Cache for full refresh) so they apply immediately instead of waiting for the next cache cycle.

Time of Day and the date variables remain settable directly per the standard runtime time-control functions in uds-time; the simulation interprets them according to the configured location/DST.

Gotchas

• Sun in wrong position for the location — check Time Zone. Most common error is leaving Time Zone default while changing latitude/longitude.
• Sun position settings ignored — that's by design when Simulate Real Sun is on. Disable it to use Yaw/Pitch/Vertical Offset again.
• Dusk Time / Dawn Time having no effect — the simulation overrides them.
• Cycle speed feels wrong despite Day Length / Night Length — Simulate Real Sun uses Simulation Speed instead.
• Moon phase wrong — Simulate Real Moon controls phase from the simulated date. To set phase manually, disable Simulate Real Moon.
• Stars look like a low-res repeating texture — Simulate Real Stars is off (default uses Tiling Stars). Enable it for the 360 star map.
• Wrong moon position for a 2050+ date — moon accuracy is calibrated for 2017; expect drift across many decades. Sun is fine.
• North isn't where you expect — North Yaw rotates the simulation. Default has north = +X.

References & source material

Docs (Ultra Dynamic Sky 9.5):

• Simulation of Real World Sun, Moon and Stars (incl. accuracy notes)
• Controlling Time of the Simulation

Related skills: uds-time, uds-sun-moon-stars, uds-setup-and-modes.