Glass Rendering Tips for Realistic Visualizations

Architectural glazing

Glass, also referred to as architectural glazing in the context of architecture, is an amazing material that provides a barrier from the elements while allowing a visual connection to the beauty around us. It provides light and even desired warmth in the cold season and is also aesthetically pleasing in many ways, including its reflective qualities.

Realistic glass rendering in architectural visualization

Traditionally, glass was challenging to represent properly in architectural visualization. Either the glass reflection or color was off, or the rendering software and settings one had to know were too complicated for the average designer. Not that they had not done it before, or were not able to learn it, but the benefit-to-cost of time and budget just didn’t make sense on most projects.

Thankfully, it's easy to create a photorealistic glass rendering with Enscape's contemporary real-time rendering software. This rendering software is always just a click away from within your Revit, SketchUp, Rhino, Vectorworks or Archicad software. The user settings are simple: more like the controls on a camera than a spaceship. And with a few simple “reflection” adjustments, we can display great-looking glass in our visualizations.

Defining glass in Revit

This article will cover how to render architectural glazing within a Revit model for a realistic-looking architectural visualization. With the evolution of Revit materials, there are three primary ways to define glass: Generic, Glazing, and now Advanced Materials in Revit 2019.

Understanding the differences between these options and how they look in Enscape is key to getting the realistic or aesthetic results you are looking for. The images above and below highlight the amazing results we can get from Enscape with just minimal effort. Not only that, but this effort is all encapsulated within the primary Revit model, not exported and refined in another format or copy of the model.

Interior Revit rendering with beautiful glazing (Credit: Dan Stine)

It is also helpful to know that Enscape has an internal material definition for architectural glazing, i.e. classic PBR: roughness, specular (F0), metallicness, etc., and they try to map the CAD’s material system onto these. However, by contrast, in Enscape’s own material editor in SketchUp, Rhino, Revit, and Archicad, you get the maximum control over all parameters.

Glass rendering in SketchUp

As just mentioned, SketchUp/Rhino, as well as Revit and Archicad have the most options for glazing when it comes to Enscape because the native materials are more limiting, supporting only a texture and transparency value, and thus there is a custom Enscape Material Editor. This editor, of course, corresponds directly to the rendering engine. Sort of like Apple making an OS for its own hardware, which removes the “middle-man” and lots of guesswork and unknowns.

When dealing with glass in SketchUp the Tint Color and Reflection Roughness are key. Here is an example in SketchUp showing three different glazing conditions and their respective settings.

Glass settings in SketchUp

1. Tint Color: typical architectural application; corresponds to visual light transmittance (VLT)

2. Transparency Texture: image used to represent a pattern in the glass

3. Albedo Color: defines the diffuse reflected light’s color, which is only visible if the Opacity is > 1% (transparency <99%); think frosted glass.

The smoother the material (Roughness -> 0%), the more it will reflect its environment, whereas a rougher surface will diffuse incoming light.

For the Transparency Texture example, notice the railing’s glass panels have a pattern. This is defined by the Texture parameter, which allows you to control the transparency using a 2D image: a map. It refers to the opacity value, so a black area (which equals zero) on the image used will result in a perfectly transparent portion of the surface, while a white area will appear perfectly opaque. Gray areas will appear partially transparent, such as glass. If you load a colored image, Enscape will automatically convert it to black and white, so you do not have to worry about that. The image can be inverted and resized as shown here.

The Refractive Index slider determines by which factor light is being bent when traveling through a transparent surface. You know this effect from looking at a glass of water or very thick glass. Air has a refractive index of 1.0, so light rays travel through it in a straight line. Water has an index of 1.33, while the index of window glass is 1.52. Diamonds, for a further example, have an index of 2.42: they bend light quite heavily. For architectural glazing, this value can be very low or 1.0 (i.e. no distortion) for efficiency.

How to render glass in Revit

Using Autodesk Revit, we can also achieve amazing results in Enscape. However, Revit has its own built-in material editor and multiple material shaders to reach similar results, with slight differences between them. The following image highlights the three options: Generic, Glazing and Advanced.

Default glass material

A Revit-provided template has the “Glass” material set to the Glazing shader option (not Generic or advanced). But the Reflectance value is set quite low so the initial impact in Enscape can be disappointing. The range of reflectance can be seen in this comparative image, with a 100 setting on the left, 50 in the center, and 0 on the right. The default in Revit is 15, which is closer to the example on the right which almost looks like there is no glass in the curtain wall system.

Comparing reflectance values for Revit’s glazing material

Advanced material

Revit’s advanced materials, introduced in Revit 2019, have different settings for the physically-based glazing shader. It should be pointed out that this “glazing” material is different than the equally new advanced “glass” material. Unlike glass, light is not refracted for efficiency in glazing (as discussed in the previous SketchUp section). The result in Enscape is a surface which is always evident from any vantage point, and the reflective quality is good.

TIP: At this time, this material type is NOT recommended to achieve optimal results in Enscape. It is still touched on so the reader can better understand the differences and limitations.

Again, the Glazing base PBR material (aka advanced material) is different than the more physically accurate Transparent (i.e. glass) material that would be used for a vase or solid glass object. Rather, glazing is optimized for architectural applications and does not produce any refraction or internal reflection. These newer advanced materials have ‘base versions’ which can be used to start new materials from scratch as shown in the image below.

Revit 2019 advanced materials base asset library

It is interesting that the new advanced material has a Visual Transmittance (T-Vis or VLT) value. Anyone specifying glazing or involved in daylight analysis or calculations will be familiar with this real-world physical property.

Revit, Autodesk Lighting Analysis, ElumTools, and, Insight also use this information for energy analysis. In the chart below we see the VLT range is from about 60 – 90%.

The transmissive color corresponds to the inherent color in the raw materials used to create the glass. The light assumes this color as it passes through the glass. Using Revit’s advanced material shader for glazing, when the correct color is entered, from a manufacturer’s data sheet for example, the Visible Transmittance (VLT) value is correctly calculated as well, as shown in the image below. VLT is the total amount of light which passes through the glass. FYI: Vitro example used can be found here.

Glazing defined with Revit 2019 advanced material – special 'glazing' shader

The following image shows the results of this material definition within Enscape. It is easy to see the transmissive color within the glass, which is great! The one big limitation with this material within Enscape, at the moment, is that the glass appears frosted when receiving direct sunlight.

Rendered image using Revit’s advanced ‘glazing’ material

Generic material

Revit’s generic materials have the most options to control the various aspects of a material in Revit, as seen in the following image.

Chart comparing adjustment options for Revit’s generic and physically-based PBR materials

In the manufacturer datasheet shown below, the glass color and reflectance can be mapped directly (tip: use an eyedropper tool in a graphics app to get the RGB value of the color). The VLT can be translated as a percentage of Revit’s 255 shades of gray; thus, 255 x VLT = RGB value (enter the result for all three). This is achieved using the Tint parameter.

Setting a generic material to align with real-world product data

Photorealistic rendering using generic material to represent real-world architectural glazing

Tip: Adjust the Luminance value within Revit's color dialog to adjust the VLT when using a color rather than grayscale RGB. This ElumTools article describes how to map an RGB value to a real-world VLT value.

Here is another example using a much lower VLT value from the manufacturer’s product line.

A variation on the previous example, using a darker VLT value

Photorealistic rendering using generic material to represent real-world architectural glazing

Visible light reflectance (VLR)

What you can adjust via the reflectivity sliders in Revit isn’t 1:1 for the VLR percentage found in manufacturer’s data sheets, but a subset of the range that is still physically plausible. Which means, for a “default” of 50% specularity we’re assuming a mapping to the actual physical value of 4% reflected light (at an angle of 0°, we call that F0). Maximum specularity (slider at 100%) is mapped to the physical value of 12%, which is actually already above the highest plausible value for pure glass materials we found in literature at that time. Also, for materials that provide 2 sliders in Revit (direct & oblique) Enscape uses the average value of both sliders.

Glazing material

Finally, let us take a look at Revit’s ‘Glazing’ material. Here we find that, when following the same steps just covered regarding real-world product data, the results are similar. Again, the tint drives the glazing’s VLT.

Setting a glazing material to align with real-world product data

Rendered image using glazing material to represent real-world glazing

Thus, of the three ways to render glass in Enscape, the latter two being the best in achieving real-world results.

NEW: Glass Material Now Available in Enscape

Since this article was originally written, Enscape has introduced a Material Library, which includes various ready-made materials, including glass.

Now it's easier than ever to select, edit, and use predefined materials within your scenes.

For more information, check out the Enscape 3.1 blog post that talks about the new Material Library and the overhauled Material Editor.

Conclusion

There is still much more that could be said about architectural glazing in buildings, or even glass in objects. But the information covered in this article should provide enough detail to achieve the beautiful results shown and additional variations by adjusting the related settings. Keep in mind, with Enscape open on a second monitor, many of these settings are visualized in real time, making the process incredibly easy.

As glazing is such an important part of architecture, it is truly exciting to see such dramatic and realistic results in a real-time rendering engine which also has a live link to our favorite 3D modeling environments.

For more inspiration, be sure to check out the Enscape Visualization Gallery to see what other customers are doing. If you have yet to give Enscape a try, download the free trial today and check it out with Revit, SketchUp, Rhino, Archicad and/or Vectorworks:


If you are a student, be sure to take advantage of a free Enscape student license!