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== Pseudo-Global Illumination ==
[[Image:Manual-Part-V-GIScheme1.png|frame|right|Pseudo Ambient Illumination scene.]]
[[Image:Manual-Part-V-GIScheme2.png|frame|right|Sky dome.]]

The [[Doc:Tutorials/Lighting/Three Point Light|Three Point Light]] and [[Doc:Tutorials/Lighting/Pseudo Area Light|Pseudo Area Light]] work well when there is a single, or at least a finite number of lights, casting distinct shadows. The only exceptions are the outdoor setting, where the {{Literal|Hemi}} Light fakes the light cast by the sky, and the {{Literal|Area}} Light where multiple spots lights fake a light source of finite extension.

The first of these two is very close to nice outdoor lighting, were it not for the fact that the {{Literal|Hemi}} Light casts no shadows and hence you don't have realistic results. To obtain a really nice outdoor setting, especially for cloudy daylight, you need light coming from all directions of the sky, yet casts shadows!

This can be obtained by applying a technique very similar to the one used for the [[Doc:Tutorials/Lighting/Pseudo Area Light|Pseudo Area Light]] setup, but using half a sphere as a parent mesh. This simulates an ambient light, as emitted by the sky.

You can either use a {{Literal|UVsphere}} or an {{Literal|IcoSphere}}, the latter has vertices evenly distributed whereas the former has a great concentration of vertices at poles. Hence, using an {{Literal|IcoSphere}} yields a more 'uniform' illumination, all the points in the sky radiate an equal intensity; in contrast to a {{Literal|UVsphere}} which casts much more light from the pole(s).
It is typically recommended that the {{Literal|IcoSphere}} is used as the basis for the duplivert.

Let's prepare a typical setup, comprising of a plane and various simple solids. We will use simple shapes to better appreciate the results.

#Switch to {{literal|Top view}} and add an {{Literal|IcoSphere}} with a subdivision level of '''2'''; a subdivision of '''3''' one yields even smoother results.
#Scale the {{Literal|IcoSphere}} so that it completely, and loosely, contains the whole scene.
#Switch to {{literal|front view}} and, in {{Literal|EditMode}}, delete the lower half of the {{Literal|IcoSphere}}, see (''Sky dome''). This creates a hemi-sphere.

This will be our "Sky Dome" where the {{literal|Spot}} lights will be parented and dupliverted. Again in {{literal|Top View}} add a {{Literal|Spot}} Light, parent it to the hemi-sphere {{Literal|IcoSphere}} ({{shortcut|ctrl|P}}) and press the {{Literal|DupliVert}} and {{Literal|Rot}} buttons exactly as in the [[Doc:Tutorials/Lighting/Pseudo Area Light|Pseudo Area Light]] example.

This results in (''Sky dome with duplicated spots'') as seen from the {{literal|Front view}}.

[[Image:Manual-Part-V-GIScheme4.png|frame|center|Sky dome with duplicated spots.]]

As you can see the duplicated lights are all pointing outwards as a result of all the normals on the hemi-sphere pointing outwards which produces an unlit scene; something we dont' want. As before we want to point the lights inward from the perspective of the hemi-sphere.

Enter {{literal|Edit Mode}} and press the {{Literal|Flip Normals}} button in the [[Doc:Reference/Panels/Editing/Mesh tools|Mesh Tools]] Panel, (''Flipping normals''), of the Editing ({{shortcut|F9}}) Context. This leads to the new configuration in ''Correct sky dome and dupliverted {{Literal|Spot}} Lights.''.

{|align=center
|[[Image:Reference-Panels-Mesh-Tools.png|frame|none|Flipping normals.]]
|[[Image:Manual-Part-V-GIScheme5.png|thumb|340px|none|Correct sky dome and dupliverted {{Literal|Spot}} Lights.]]
|}

To obtain better results select the original {{Literal|Spot}} Light and change its parameters to a wide angle with soft boundaries using the [[Doc:Reference/Panels/Shading/Lamp/Lamp|Lamp]] and [[Reference/Panels/Shading/Lamp/Shadow_and_Spot#Spot_type|Shadow and Spot]] panels configured as such:

From the {{literal|Shadow and Spot}} panel:
*Enable {{literal|Buf.Shadows}}
*{{Literal|SpotSi}}= '''70.0'''
*{{Literal|SpotBl}}= '''0.5'''; with suitable
*{{Literal|ClipSta}} and {{Literal|ClipEnd}} values = '''5''' and '''30''' respectively.
*{{literal|Samples}}= '''6.0'''
*{{literal|Soft}} = '''12'''

From the {{literal|Lamp}} panel:
*{{literal|Energy}} = '''0.1'''

Remember you are using many spot lights, so each must be weaker than the original spot light.

[[Image:Manual-Part-V-GIScheme7.png|thumb|400px|right|Spot Light setup.]]
Now we are ready to render the scene. If materials are created and assigned and a world set, the result should be that of (''{{Literal|Spot}} Light setup''). Note the soft shadows and the 'omnidirectional' lighting. Even better results can be achieved with a subdivision level '''3''' {{Literal|IcoSphere}}.

This technique effectively substitutes, at a very high computational cost, the [[Manual/PartV/Lamp_Types#Outdoor_Light_example|Hemi outdoor setting]]. It is possible to add a directional light component by faking the Sun either via a single {{literal|Spot}} light or with an {{Literal|Area}} Light.
{{clr}}

[[Image:Manual-Part-V-GIScheme8.png|frame|right|Making spots denser in an area.]]
A possible alternative is to make the {{Literal|IcoSphere}} 'less uniform' by subdividing one of its faces a number of times, as is done for one of the rear faces in (''Making spots denser in an area''). This is done by selecting a single face and pressing the {{Literal|Subdivide}} button,
again using the {{Literal|Mesh Tools}} Panel of the Editing ({{shortcut|F9}}) Context. Then de-select all, re-select the single inner small face and subdivide it again, and so on.
{{clr}}

The result is a very soft directional light together with a global illumination sky dome or, briefly, an ''Anisotropic'' sky dome (''Anisotropic skydome render''). This is quite good for cloudy conditions, but not so good for clear sunny days. For really clear days, it is better to keep the sky dome separate from the Sun light, so as to be able to use different colours for each.

[[Image:Manual-Part-V-GIScheme9.png|thumb|500px|center|Anisotropic skydome render.]]

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