A windsock is used as a basic indicator of wind speed and direction. An aerodrome is required to provide and maintain a visual indication of wind direction and strength, typically located at the end of the runway or at least visible to pilots on final approach and prior to takeoff.
Direction of the sock illustrates wind direction, while wind speed is visible by the amount of tension found in the sock (no wind translates to more droop). The pole must be completely vertical and the wind sock able to move freely in a complete circle.
ICAO standards specify a wind sock to be cone shaped, 3.6m long and 0.9m in diameter (at the mouth). Previously wind socks have been two colours to help judge wind speed, however ICAO standards only mandate a single colour - orange, yellow or white - to stand out from the background.
There is no specification for product material, but should be durable and well-maintained, therefore windsocks are usually manufactured from durable polyester and waterproofed.
They should be visible from an altitude of 300m, active in wind speeds of three knots (5.6km/h or 3.5mph) and must indicate wind direction to within ±5°.
About this project
Creating a windsock animation is a relatively straighforward process. The basic wind simulation was created using Houdini's position based dynamic framework known as Vellum. The speed of Vellum's cloth solver was the primary reason for choosing this approach which made it easy to adjust wind speed.
Maintaing performance for the realtime version of the animation required keeping the polygon count low, and the animation short. A seamless loop was created with the SideFX's make loop node.
This model does not take into consideration night visiblity. ICAO note that wind direction indicators must have lighting if the airport is open for night operations. This is usually by floodlighting overhead or lighting on the mounting pole. A future update will add support for LED lighting.