Radiosity rendering is very different from other rendering modes, and requires a different workflow process to achieve a successful result.
A: Radiosity is one way for a computer to simulate the indirect lighting that occurs when lit surfaces transfer their energy to other surfaces. To calculate this lighting, all the surfaces in the model are converted into triangles and the brightest triangles are visited in turn. Light from each triangle is re-emitted to its neighbors, until some amount of energy has been accounted for, and then the radiosity solution is considered to be finished.
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There is a large contrast between the darkest and brightest parts of the model, or there are large color contrasts among the lit areas in the model.
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You can quickly produce satisfactory lighting by combining existing VectorWorks light objects, or easily “fake” the indirect lighting with fill lights.
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There is not significant contrast between the brightest and darkest areas of the model, or there is not much color contrast between the lit surfaces in the model.
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A: Ambient light is a catch-all phrase for the remaining light that is bouncing around in the model. Radiosity can be thought of as a way to correctly calculate and “localize” the ambient light. As more energy is accounted for in the radiosity solution, the (un-localized) ambient energy decreases until all the light energy has been localized. Radiosity can be used as a “fast” way to produce a more accurate ambient term, and apply some of the brightest light to specific regions of the model. Note that any ambient lighting set by the Set Layer Lighting Options command should be turned off for a radiosity rendering (set the ambient lighting control options by clicking Ambient Options from the Radiosity Options category of the Custom Radiosity Options dialog box).
A: Radiosity uses a lot of memory because all of the model's geometry must be duplicated and converted into triangles of a certain size, and assigned energy values. The more detailed geometry in a model, the more memory the radiosity processing will use and the more time will be required to re-emit light energy from each triangle to its neighbors. Also, the higher the render mode's detail settings, the more triangles are produced, resulting in larger memory requirements and more time to re-emit the light energy onto each triangle’s neighbors. Doubling the number of surfaces in a model actually quadruples the time required for radiosity processing.
A: Both rendering processes create indirect lighting effects. However, final gather rendering is not affected by the model geometry, in that it does not duplicate the geometry and convert it into triangles with assigned energy values. Final gather rendering uses one bounce of light to create indirect lighting effects, while the light energy in a radiosity rendering is emitted and re-emitted until the solution is complete. Radiosity avoids some problems relating to noisy or speckled foregrounds in renderings, while final gather rendering avoids the triangulation artifacts seen in some radiosity images. Final gather rendering takes advantage of multi-threaded processors, while radiosity does not. For very complex models, final gather rendering enabled in Custom RenderWorks may provide a satisfactory rendering which would take too long to realistically achieve with radiosity alone.
The benefits of both types of indirect lighting effects can be achieved by combining them. For the most important (bright) objects in the model, use radiosity, and exclude the remaining objects from the solution. Final gather rendering can finish the indirect lighting effects.
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Use the highest-level geometry you can to model your objects. It is much better to model an object as an extrude, sweep, boolean solid, or a NURBS surface than as a mesh. The worst way to model for a radiosity rendering is to create a detailed object as a set of small, individual 3D polygons.
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Eliminate 3D details that are not going to be significant to the rendered image or the indirect lighting. For example, if you model a staircase's individual bolts and threaded screws, each of these will be contributing unnecessarily to the memory and time required for the radiosity solution. The Median Obj Size shown in the Custom Radiosity Options dialog box will have an unusually small value when the model consists of mostly tiny geometry.
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Enable final gather rendering effects to handle the details excluded from the radiosity solution (select Use Final Gather in the Custom Radiosity Options dialog box).
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Limit the size of large ground planes and landscape surfaces to the minimum size needed for the rendered image. Depending on the render mode's detail settings, the large surface area can produce millions of triangles that do not significantly light up the building because their energy is emitted mostly into space.
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If geometry must be visible in the rendered image but will not contribute significantly to the indirect lighting, consider applying per-texture or per-object radiosity overrides to them to help the radiosity processor ignore them.
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A: The reflectivity shader controls how much light is re-emitted from a surface. To control this amount, apply a texture that uses a reflectivity shader, and adjust the reflectivity shader's Diffuse Factor. The default reflectivity shader when one is not assigned is Matte, whose Diffuse Factor is set to 100% by default.
In addition, use radiosity overrides. “Turn off” or “turn on” radiosity for specific objects or textures by using the override checkboxes shown in the Edit Texture dialog box and the Object Info palette's Render tab. For example, to render a ground plane with direct lighting but not include it in radiosity processing for efficiency, you can set the Radiosity Override checkboxes to not emit and not receive. This effectively removes the ground plane from radiosity processing. If a patch of grass needs to re-emit onto the side of a building, split the ground plane into a large one that does not emit or receive and a “skirt” around the building that does emit and receive.
Through the Radiosity Optimizations dialog box, model parameters can be set so that only certain objects re-emit indirect light, and all other objects either just receive indirect light or do not participate at all in the radiosity processing. One combination that can be produced is one where only the light on a floor is re-emitted onto the rest of the room, which becomes one bounce as in final gather rendering.
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Using Custom Radiosity render mode, select the Include Visible Surfaces Only checkbox in the Radiosity Optimizations dialog box. This means that only the visible building facade will be involved with radiosity processing. The objects and surfaces that are behind the facade will not be included in the radiosity processing.
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Set large ground planes and tree image props to not emit or receive, using either Edit Texture or Object Info palette radiosity overrides.
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Set the Obj Inclusion slider in the Custom Radiosity Options dialog box such that only the largest lit surfaces will emit (gray), and the smaller details like window mullions and door knobs will only receive (red).
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If any surfaces are not visible that do produce significant indirect lighting (like flat roof surfaces that aren't visible in the current view), they can be forced to participate despite not being visible by setting either an Edit Texture or Object Info palette radiosity override to emit and receive.
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Enable final gather rendering effects to handle the details excluded from the radiosity solution (select Use Final Gather in the Custom Radiosity Options dialog box).
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In the Custom Radiosity Options dialog box, deselect the Create Ambient from Remaining Energy checkbox. This makes it possible to stop the radiosity processor sooner without having additional ambient lighting that makes the model overly bright or overly saturated with color.
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