Wind

Introduction

Nova expresses wind as both ground/sea level wind and variable wind layers. This has an effect on several elements in the scene such as the sea state, the wind socks, effects like smoke columns and the movement of cloud layers.

Types of Wind

Sea State Wind

Sea State wind controls the look and movement of 3D water surfaces such as oceans and lakes.   

Wind Layers

Wind Layers are used to control effects on the terrain such as windsocks and smoke markers. The wind layer definitions will also impact cloud layers.  Nova allows for up to 4 points to be defined.  The wind speed and direction for any given altitude is interpolated between these points.  If wind_layer_hgt[0] is 0 feet and wind_veloc[0] is 20 knots and wind_layer_hgt[1] is 10000 feet and wind_veloc[1] is 30 knots, then the wind speed at 5000 feet altitude would be 25 knots. An important point to understand is that wind_veloc[x] has an off condition of 0, so if you want to achieve no wind, use .001, not 0.

Wind Parameters

Effects of the Wind

Wind Socks

The wind_veloc and wind_dir affect the wind sock for the lowest wind height (wind_layer_hgt). If you were to set multiple wind layers to the same height, lowest wind height would be the last one encountered. For example, if:

• wind_veloc[0] is 7 knots
• wind_dir[0] is 45 degrees
• wind_layer_hgt[0] is 0 feet
• wind_veloc[1] = 14 knots
• wind_dir[1] = 90 degrees
• wind_layer_hgt[1] = 0 feet

Your wind sock will be oriented to 90 and be perpendicular to the horizon because [0][1]both have the lowest value and [1] was encountered last. 

Another important point is that wind_veloc has an off condition of 0. Wind of zero doesn't mean 0 knots wind it means wind off. This matters because if the lowest wind layer is 0 but wind_veloc[0] = 0, then it fails over to the next lowest layer of wind to grab the velocity and direction.

For this reason, you should set all the wind_layer_hgt[x] to unique values, make sure that their velocity is set to greater than 0 and know that only controlling the lowest one is impacting your wind sock.

CIGI Control for Wind

Wind Layers

Atmosphere Control Packet for Wind Layer

This packet is a simple way to control all of the wind layers at once and set the wind to one global value.  The values passed in this packet will fill into all of the wind_dir, wind_veloc variables.  The wind_layer_hgt will be set at 0, 2000, 4000, and 6000 feet for the layers.

Weather Control Packet for Wind Layers

If you want to control wind layers individually you must send the Weather Control Packet AFTER the Atmosphere Control Packet in the corresponding frame.  If not, the values in the Atmosphere Control Packet will overwrite the wind layer values.

Sea Wind

Weather Control Packet for Sea Wind

The sea wind speed and direction can be controlled via the weather control packet with a Layer ID of 11.  This packet will also control other variables related to the sea. 

Legacy User Defined Packet for Sea Wind

Aechelon supports a Sea State User Defined Packet to control all the variables in the internal nova sea_state structure including wind speed and direction.