Clouds covers

Clouds covers aggregate clouds together to create a sky coverage. The principle is that an opacity map will define the position of clouds and then clouds added to the cover will be scattered in areas where the cover map is opaque. Below a clouds cover with a high contrast:

Creating a clouds cover

Let's create a clouds cover first. As for all other documents:

  1. Click on the cover creation button in the clouds covers documents tree view,
  2. Double click on the created cover to open it.
  3. Set the source opacity map to define the cover.
  4. Drag'n drop the cover in the current scene. Select the altitude of the cover.

Once there, we can see the cover itself. It does not contain any cloud yet. So this is the bare clouds cover map that we display. A default clouds cover has a size set to 1000 kms. So you may need to move the camera to a high altitude to see the cover entirely.

Setting up a clouds cover lighting

The first parameter can be used to provide a bit of bumpiness to the clouds cover. The cover itself has no thickness as its a texture mapped onto the planetary surface. So adding a bit of normal bending will generate some bumps - like in a normal map calculation - over the cover:

Then, there are three lighting parameters that can be modified to change the cover lighting and the way it reacts to the sun and sky lighting: the sun multiplier, the sky multiplier and the ambient occlusion coefficient. Like for all rendered elements in NDunes, the ambient occlusion still plays a role in estimating the amount of light interaction with other elements of the scenery. Below is an illustration of a few settings values:

Adding clouds to a cover

Clouds that have been prepared for the display can be added to a cover by dragging them into the list of clouds of the cover directly:

Then, the cover will show up clouds up to the clouds display distance specified in the Settings panel:

We can adjust the fading between the clouds cover and the clouds by using the distances specified in the Settings panel:

Here, the fade start is almost identical to the fade stop and this reveals the connection between the two layers. Then, the shading terms of the clouds cover (Setting up a clouds cover lighting) and the clouds shading terms can be adjusted to reduce the transition.

Note that generally speaking it's required to see clouds at extremely high distances. 300 kms may be a must have to see clouds up to the horizon.

Cloud setup in a cover

Once a cloud has been added to a cover, we can see its scattering parameters:

Cloud opacity range in a cover

On dropping a cloud that has been calculated for a given opacity amount, NDunes will automatically generate lower and upper limits of opacity for that clouds. This means that the cloud will only have chance to appear in cover areas where the cover opacity falls in between the min / max opacity for that cloud. This is illustrated below:

The cloud has a mean opacity of 68% so by default the cover will spread it out in cover areas whose opacity is in between 51% and 85%, so that the cloud design remains correct. NDunes will change the opacity of each scattered cloud to adjust it to the opacity of the cover where the cloud is spreaded. This means that if a cloud is set to be spreaded in a cover area which is mostly transparent, the cloud's opacity will be modified dynamically to match that transparency.

Then, opacity boundaries are freely editable, and the same cloud can be set to be appear anywhere. Below an example where the cloud's opacity range has been increased to 0% - 100%, so that the cloud appear everywhere in the cover:

Clouds covers rendering options

There are several rendering options that can modify the effect of a clouds cover. Some of them are Settings such as: