Chief Architect RTRT tips and tricks

X-13 PBR-RT TIPS

A breakdown in response to growing frustrations with PBR-RT ………by Rene Rabbitt

(Items that are specific and searchable terms in CA have capitalized first letters)

There is nothing "wrong" with the new Astral PBR RTRT option. A better understanding of a modern

rendering engine may help alleviate some issues.

• In RTRT a low sample rate is used in live camera views.

• For exported presentations with images similar to a CPU-based RT, set your Maximum Export Samples

as low as needed to eliminate fireflies and light leaks. The higher the sample rate in RTRT Rendering

Techniques, the better the image (up to a point where benefits are negligible).

This only applies to the Export Image Tool.

• A sample rate in basic terms is the number of samples from a camera of a given Objects Material ID as

it applies to the geometry of an objects, including colors, lighting, shadows etc. The more times

something is sampled the less aliasing ( jaggies) there exists in a final image.

• The more light exists in the scene the easier it is to Sample.

• You must supply ample light in adjacent rooms for the RTRT engine to properly process and "trace"

your scene. Devoid of light, your exterior will be overly exposed, your interior may be underexposed, and

you may have fireflies or light leaks.

• Ensure that your active Light Set is on and illuminating your scene, which is accessed a number of ways,

one being the Edit Active View tool, in the Camera Panel, under the Lighting Section.

• With ample lights, an interior scene Rendering Technique Options might have an exposure from .15-.35,

a Maximum Sample Rate of 500-1500, Brightness between -10 to 0, and Backdrop intensity between 100-

1000. This is not and never will be a universal setting, each scene needs adjustment according to the

amount of light available to that scene.

• If your scene is underexposed you may need to adjust your lighting including the lumens of your light

fixtures.

• Sun settings will do very little to help overexposure, underexposure, light leaks or any other trace related

problems. This is the nature of a tracing engine.

• Typical problem causing issues:

Caustics, Lights near transparent or translucent surfaces, lights of high Lumen values in one room

juxtapose to lights of low lumens in an adjacent room. High resolution bump/roughness/normals maps in

materials. These issues all cause difficult scenarios for attenuation and aliasing.

Some of the fixtures being used are not optimized for this new engine. Consider changing the material

Properties of any glass that is in close proximity to a light source. Changing the glass material of a light

Fixtures that are turned on in a RTRT camera from Transparent class to General Material with high transparency can yield much more predictable results. Same goes for situations when inside cabinet

lights do not show up in RTRT behind Transparent Glass windowed cabinet doors.

There is a lot more to this, you can have some success with this info, but this barely scratches the surface.

For some incredibly good generalized rendering info, read the Thea Render Manual (free online). It has

some fantastic info in it that applies to all rendering engines.