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When is a Hole not a Hole? Rendering with Cutouts and Transparency Maps

If you have ever needed to render a scene in either Revit or 3DS Max which has objects such as sun-shades, chain-link fencing, perforated screens etc. then this is the blog for you.

What you don’t want to be doing it actually modelling the object in 3D. First, this is extremely time consuming and, unless you are running a machine of monstrously high specifications (we’re talking military defence processing power) then your ability to navigate your model is going to be severely affected. For the geeks out there - If you think about the math involved e.g. take a square sheet which has 6 faces by default and then punch a single square hole in it. Now if has 10 faces So the same sheet with 2000 holes would have 8006 faces, all of which require processing. Now multiply that for a 500 Mtr chain-link fence and see what happens.

Finally, there’s also a high chance that you won’t live long enough to see the final render completed (that’s if your processor doesn’t burn out during the process). 

In the image below of the chain-link fence you aren’t looking at an intricately modelled mesh fence. Nope! What you are actually looking at is a series of post (modelled in 3D) but with simple solid planes placed in-between.

cutout transparency filter

 

So ‘how do we overcome this?’ I hear you cry.

Well, both Revit and 3DS Max have a neat trick to overcome this problem: 

Revit allows you to apply both a Cutout and a Transparency map to a material.
Cutout maps make the material partially transparent. By applying a black and white image, any object which has this material applied will be transparent where the black portion of the image is and opaque where the white part is. Transparency maps can be used for frosting or translucent effects. The image used can grey scale and this controls the translucent effect – the darker the more transparent.
You can combine a Cutout with a Transparency to make a material take a particular shape or pattern. Cutout areas do not reflect, but Transparency areas can.

cutout transparency filter 2

It’s a similar story in 3DS Max, though the process it to create a standard material and then add your B&W or Greyscale image to both the Diffuse and Opacity inputs:

cutout transparency filter 3

So the question was ‘When is a hole not a hole?’ and the answer is ‘when it’s a solid plane or object and has a Cutout or Opacity map applied

Even though the sun shades in the image below are solid and only have the Cutout map applied to their material, not only can you see through them, but light also passes through and falls on opposing surfaces as it should in the real world.

cutout transparency filter 4

And as a final note. The image above was first rendered in Revit on my laptop at the highest quality setting. It took just over 1 hour to finish. I then rendered the same scene out from Revit but this time via the Render in the Cloud option and it was completed in just over 2 minutes.

So if you’ve ever wondered if rendering via the cloud is worth the credits (2 in this case) versus your time. Then there’s your answer!

render in cloud

 

If you would like to learn more about Revit, 3DS Max or our training sessions, please do not hesitate to get in touch by following the link below:

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