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Portale sind beispielsweise für Innenszenen nützlich, bei denen Tageslicht durch kleine Öffnungen eindringt und sich eine effiziente Abtastung als schwierig erweist. Indem diese Öffnungen ausdrücklich als Portale markiert werden, kann das Rendermodul die Szene schneller und in höherer Qualität rendern.
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Für alle Luminanzen: Wenn diese Option aktiviert ist, wird das Portal innerhalb der Szene für alle Luminanzen mit Tageslicht verwendet, unabhängig davon, wie dieses Tageslicht erstellt wurde (Zeichnungsluminanz oder Grafikluminanz). Wenn sie deaktiviert ist, wird das Portal nur für Luminanz dieses Objekts verwendet. Die Option ist nur dann aktiv, wenn die Option Als Tageslichtportal verwenden aktiviert ist. Diese Option ist standardmäßig aktiviert.
Using portals
Portals are objects (surfaces) that control the flow of photons from the light source. More precisely: the spatial configuration of the photon's flow.
The simplified algorithm is the following: if the photon has not passed through the portals, it is not considered in the calculation of illumination and the CPU time is not spent on it. Instead of it the next photon is launched (generally at random). This continues until the number of photons passing through the portals will not be equal to the target parameters of the light source. In our case it is a sky light (RedSDK supports only sky lights for the portals). In the case of absence of portals all launched photons are involved in the calculation of the illumination.
So, portals allow you to concentrate the quality and the intensity of the light in the right places of the scene. This facilitates the creation of a scene with proper lighting and improves the speed of calculation.
The main purpose of the portals is using them for the openings through which the outer sky light penetrates. Portals need not to be rectangular necessarily. The portal may consist of any set of surfaces. At the same time you should not make the portal very complicated (for example as an ADT window), because of the additional time is required to clarify whether the photon passes through a portal or not. Ideally it should be 1 rectangular facet.
In TurboCAD any 3D primitive can be a portal. This simplifies creation of portals. It should be noted that in this case the geometry of this primitive is not loaded into the scene. In other words an option 'Use as skylight portal' is similar to the option "Load to render luminance only".
Below is shown the effect of the portal's size on the lighting quality and intensity. By increasing the size of the portal 2 times the quality worsens 4 times (at the square).
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