Guide to choosing a rendering method

MicroStation provides a comprehensive range of rendering options, to let you produce shaded images from the very basic through to photo-realistic.

During the design process, quite often it is helpful to use the basic rendering modes, such as hidden line, filled hidden line, constant, or smooth, to quickly render a view as an aid to visualizing the design. Sometimes, when working in wireframe mode, it is possible to “lose your place” with regards to the orientation of the view.

It can be difficult to determine the orientation of a model when viewed in wireframe display.

Using one of the basic rendering modes is a quick way to verify the view orientation.

When the view is rendered, it is easy to see how it is rotated. Both the above images look the same in wireframe.

An added advantage with these rendering modes, is the option of using graphics acceleration, which lets you manipulate the rendered view in real time. Similarly, with graphics acceleration, you can preview animations on screen. None of these basic rendering modes display shadows.

When it comes to the finished product, creating a still image or an animation, several choices are available. For example, the choice of a photo-realistic rendering mode can be dependent on the type of model and the materials present in the model. Where accurate shadows are required, Ray Tracing should be used. While Phong rendering can generate shadow maps, these are an approximation of the shadows. With both Radiosity and Particle Tracing, you can specify that the final display is Ray Traced. Similarly, for both these rendering modes, you can turn on Ray Trace Direct Illumination, which will produce sharp shadows from any direct illumination from light sources. Shadows from reflected light, still will produce softer shadows.

For most situations, Ray Tracing and Particle Tracing present straightforward methods to produce high quality photo-realistic images. Particle Tracing was specifically designed to handle large designs, and all light paths. Additionally, it is easier to understand, and easier to use than Radiosity solving. As a general rule of thumb:

• Particle Tracing is best in terms of getting a "full" solution. That is, all light paths are considered.

• If you have no diffuse reflections or caustics, ray tracing might be sufficient, and quicker (you can consider it a sort of subset of particle tracing).

• If you have a small design, and no specular effects, Radiosity might be quicker than PT, but requires a steeper learning curve.

Following are general guidelines to help you choose the appropriate rendering mode for common situations.

In the following examples, where Radiosity and Particle Tracing are used, the final display is set to Ray Trace, and Ray Trace Direct Illumination is turned on.

No diffuse or specular reflection of light

Models that have no diffuse reflection, or caustics, normally can be rendered successfully with Ray Tracing alone.

In the example below, which has no diffuse or specular reflection of light, the same model has been rendered using Particle Tracing with Ray Trace Direct Illumination turned on (left) while Ray Tracing alone has been used in the image on the right. In this example, Ray Tracing produces an equivalent result, but quicker than using Particle Tracing.

Ray Tracing (right) can produce equivalent results to Particle Tracing (left), where no diffuse or specular reflections are present.

Diffuse reflections

Models that have diffuse reflection, but no specular reflection, can be rendered using Radiosity, or Particle Tracing. For these models, Ray Tracing alone will not produce as good a result as Radiosity or Particle Tracing. This is noticeable particularly with interior scenes where the reflections from walls contribute much to the overall lighting, commonly known as global illumination.

In the example below, ray tracing alone does not produce as good a result as achieved with Radiosity or Particle Tracing. In the ray traced image, there is no reflected light illuminating the ceiling, as would be the case in real life.

Where diffuse reflections predominate, Ray Tracing alone may not produce the required result.

Both Radiosity and Particle Tracing produce more natural looking images than ray tracing alone, because they account for diffuse reflection. In this case, the ceiling is illuminated by reflected light. Generally, Particle Tracing is the easier option to use, though it is possible in some smaller models that radiosity solving will produce a faster result.

Both Radiosity (left) and Particle Tracing (right) take into account diffuse reflections.

Similarly, using this same example, the result is even more dramatic when the only illumination for the scene is provided via a single external distant light source coming through the windows. When using Ray Tracing alone, you would need to add some Flashbulb, or other lighting, to provide illumination to the portions that are in dark shadow (as shown below).

Ray Tracing alone, with no additional lighting (left) and with Flashbulb turned on (right)

Again, both Radiosity and Particle Tracing produce more natural looking images by taking into account the diffuse reflections from the walls. Particle Tracing also accounts for the specular reflection component, if any.

Both Radiosity (left) and Particle Tracing (right) produce more natural looking images.

Diffuse and specular reflections

Models that have both diffuse reflection and specular reflection require Particle Tracing to correctly display all features of the image. With Radiosity, only the diffuse reflections are accounted for, whereas Particle Tracing accounts for specular reflections as well. For these images, Ray Tracing alone does not display either diffuse or specular reflections.

In the examples below, the image on the left uses Radiosity, while that on the right uses Particle Tracing. In the particle traced image, you can see that the light has been reflected from the polished table and the silver tray. In the image that uses radiosity, only the diffuse portion of the light has been reflected, which is very little in this instance.

Particle traced image (right) displays both diffuse and specular reflections (such as the light reflecting on to the wall from the table and silver tray), while the radiosity image (left) displays only the diffuse component.