A horizon space is a space that lives in the horizon -or background- of a space. Horizons are used to create dynamic sky-boxes comprised of stuff that lives in the distance. For instance, you can place a cube-map into a horizon to surround the viewer inside a 360 image. Another use would be to place large sound sources inside a horizon space to immerse the viewer in sounds that stay regardless of the viewer's position.
Let's take a look at the default space that is created when you first enter Simmetri or go to File/New. The default TerrainSpace created (the foreground space) has as its horizon space a SkySpace (the background space). We can see this by viewing the root properties of the TerrainSpace.
In this case, a SkySpace is a simple space comprised of a simulated sky whose properties we can alter to create sunsets and other time of day effects. Along with defining the horizon of the space, you can also set its distance scale. The 'Distance Scale' property let's us set how the scale of the horizon is defined in the context of the foreground space. For instance, 1 unit in a horizon space rendered at a distance scale of 1000 would be = 1000 units of the foreground space. In other words, if we placed a sphere with a radius of 1 into a horizon space and rendered it with distance scale set to 1000, it would appear on the horizon from the foreground space as if it had a radius of 1000. The sphere would also parallax shift accordingly as the camera is moved.
Since horizon spaces are just spaces, they too can have horizon spaces. This nesting of spaces allows us to define various background layers. We can see an example of this when we use the 'Horizons / Pyramids' tool from the toolbox. It creates a view that looks something like this:
In this case, the foreground space is a TerrainSpace, whose horizon space is an OpenSpace, that contain the pyramids objects. Finally, the OpenSpace's horizon space is a SkySpace that renders the sunset. Since the 'Inherit Atmosphere' property is set to true for both the TerrainSpace and OpenSpace, the SkySpace's atmosphere (which includes lighting and haze effects) is passed through to the foreground space.
- You can select the horizon space and display its properties by clicking on the sky. If you click the ground, you will instead select the foreground space.