Tipniques: Design Visualization with Revit – Which Rendering Engine to Use?

August 15th, 2013

Introduction

Revit has powerful tools for rendering and animation. Designers, architects and engineers can generate images to communicate their design intent more clearly to clients and other members of their design team. You can render with the mental ray rendering engine, the Autodesk 360 Cloud Rendering service or the Ray Trace Visual Style. All three choices give excellent results and have their own unique positive and negative aspects.
As the examples below show, the three rendering engines have very distinctive looks.

Mental ray render, Best Quality, 10 Minutes rendering time

Cloud Render, Best Quality, 1 minute rendering time

Ray Trace visual style, 10 Minutes rendering time

Design Visualization in Revit

The Revit model must be a complete building model to render properly. Light sources will only render properly if the building model is a closed space that has floors, walls, windows, doors and roofs. Ceilings are required if ceiling-mounted light fixtures are part of the interior lighting design of the building. Materials and textures should be applied to all objects (for example, paint on the walls, glass in the windows and doors, and flooring materials). You can render 3D views of the building model. The rendered view could be a camera view or the default {3D} view in the Project Browser.

Rendering in Revit

Method 1: mental ray

PRO: High Quality Renders

CON: Takes a long time to render

Mental ray allows you to define render settings such as Quality Level, Exposure settings and setting the background to Sky or Image in the Rendering dialog.

Rendering an image can be a time-consuming step if the quality level is set to Best or there are glossy or transparent materials on objects. When you are working on a rendering in Revit, you need to start at a lower level of quality then the final image will require. When you first start testing your rendering settings, start at a Draft quality setting so the image will render quickly. Then, gradually increase the level of quality of the image as your design progresses.

There are many settings unique to mental ray in the Rendering dialog that allow you to fine-tune the quality of the final rendered image. These settings (located on the Render dialog, Quality, Setting, Edit) include controls for image precision, reflection and transparency options, and indirect lighting and sky illumination settings. Using these advanced settings typically increases the quality of the rendered image, but also takes longer to calculate. Increasing the quality level of each advanced setting adds to render time, and can substantially increase render time when several of the settings are increased simultaneously. Some settings may only increase the rendering time by several minutes, others may add several hours (or even days) to the rendering time. mental ray also allows you to enable Daylight Portals when you render your image to help improve the quality of this light entering the interior view. Daylight Portals direct the sunlight through the windows, doors and curtain walls that contain glass and improve the amount and effect of the sunlight.

Method 2: Render on the Cloud with Autodesk 360

PRO: Fast! Fast! Fast!

CON: Less control over render settings

One of the main complaints about rendering high quality images in Revit is that it can take an extremely long time to render an image and the machine performing the render cannot be used for other production work. A solution to this problem is Cloud rendering. Rendering information from the Revit model can be sent to the Autodesk 360 Cloud service, and the rendering is performed on the Cloud and does not use the resources of your local computer. This functionality is one of the services that are provided to customers that have an Autodesk Subscription. If you have purchased a Revit, Building Design Premium or Building Design Ultimate Subscription, you have the ability to render on the Cloud. On average, a rendered image that takes Revit an hour to render will typically take less than 5 minutes on the Cloud.

Once your Revit model is ready to render, simply go to View > Render in Cloud to access Cloud rendering in Revit 2013 and 2014.

You will then be prompted for your Autodesk Account ID and Password (these are the ID and password that you have set up for accessing your Autodesk Subscription information). Once signed in, you will see a dialog that explains the Cloud rendering process.

Then, you set the rendering settings that you require, These settings are very similar to the settings in the Revit Rendering dialog. One thing to keep in mind is that the rendered images from the Cloud do not use mental ray as the rendering engine, so a Cloud rendered image will look slightly different than the same scene rendered locally in Revit itself.

You will be able see at the top of the Revit UI that the image is being rendered on the Cloud. When the render is complete, you will notified in Revit and you will be sent an email.

To view the rendered images, got to View > Render Gallery, and a website will display showing completed images (as well as any images still being processed).

An image in the Render Gallery can be selected, re-rendered with different settings, or downloaded from the gallery.

For Revit 2012, you can go to the New Rendering tab of the Render Gallery and download the Revit 2012 Add-in for Cloud rendering (Revit 2012 Update is also required). Revit 2013 and 2014 do not require an Add-in; it is automatically installed. You can also render to the Cloud from AutoCAD.

Since Cloud rendering is so fast, you can use it when giving presentations to clients. One possibile application would be to explain different Design Options in a Revit model to a client, receive their input, make changes to the model, and then send renders to the Cloud as each change is finalized. After a few minutes, complete rendered views can be downloaded and shown to clients, allowing almost instanteous feedback with photorealistic images. 

Method 3: Ray Trace Visual Style

PRO: Interactive

CON: Less control over render settings

The Ray Trace Visual Style is an interactive rendering environment. Any 3D view in Revit can be assigned the Ray Trace style. Ray tracing simulates the path that light rays take as they bounce around and off surfaces, just as light does in the real world. The render settings are located in the Graphics Display Options (located on the same menu as the Visual Style options at the bottom of a Revit view). These settings are very similar to the settings in the Revit Rendering dialog.for mental ray but do not have the advanced options available.

With Ray Trace, you have three options in the View ribbon: Stop, Save and Close. As soon as you switch to Ray Trace, the view will start rendering at a low quality setting. As long as Stop or Close is not selected, the render will continue to process, gradually increasing in quality. The unique feature of Ray Trace is that it is an interactive view. As it is rendering, you can Pan, Zoom, change the Graphic Display Options, and use the View Cube. The render will reset and keep rendering as you interact with the view. When the quality level is high enough, you can Stop and then Save the image to the Project Browser (where you can then export the image by using Export > Image and Animations > Image). As with a Cloud rendered image, the render will look slightly different than the same scene rendered with mental ray.

Summary

Using the rendering capability of Revit, designers, architects and engineers can generate images to communicate their design intent more clearly to clients and other members of their design team. The mental ray rendering engine offers a high level of quality and a large toolset of advanced options, but can take a long time to render. The 360 Cloud rendering service is useful when an extremely fast render is needed and where advanced settings are not needed and some color shift and material/texture changes can be tolerated. The Ray Trace Visual Style is useful when you need to interact with a view to adjust settings and camera angles on the fly and where advanced settings are not needed and color shift can be tolerated.

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About the Authors

Tod Stephens

Tod Stephens

Tod Stephens obtained his Bachelor’s degree in Electrical Engineering from Cleveland State University and his Master of Science degree in Education and Technology from Walden University. He has been working in the CAD, BIM and visualization field for over 15 years. He has worked for Autodesk resellers as an Architectural Applications Engineer and is currently conducting Revit and 3ds Max training for Advanced Technologies Solutions. Tod is an adjunct instructor at the International Academy of Design teaching AutoCAD, Revit Architecture and 3ds Max courses for the online BIM department. Tod is a Revit Architecture Autodesk Certified Instructor, 3ds Max Autodesk Certified Instructor as well as a Certified Professional in AutoCAD, AutoCAD Architecture and 3ds Max Design. He has several Revit/ 3ds Max Tutorials on YouTube under the nexgenviz channel (30 Videos, over 750,000 Views to date). Tod also has several Autodesk specialization certifications: Advanced Specialization in MEP Engineering Systems, Structural Engineering Systems and Simulation.

 

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