VR is different than traditional architectural rendering in that it has limitations for performance. Previously, architectural renderings took a few hours to multiple days. With VR experiences, we must render a new image 60 to 90 times per second! This is quite a drastic change.
Bad VR performance can lead to judder and VR nausea. We must therefore optimize models to use the least amount of triangles and textures possible. While a lot of the optimization is done on our servers, we can only do so much if the model is very complex.
One of the most basic ways of calculating a model's complexity is through it's triangle count. We will go through some tricks, tools and strategies to reduce triangle counts in your Revit architectural models.
There are a few strategies for parsing down model complexity for Revit. Here are a few pointers:
- By far the quickest way to reduce triangle count is simply to take a scope box of the model you're trying to upload and scope the model down. The remaining model in the 3D view can then be uploaded to programs like InsiteVR.
- Set specific 3D views for your VR exports depending on what you are looking to demonstrate. Will you be going into the plenum and looking at in-wall plumbing? Are you going to check fire exit stairs? If not, hide these objects for the VR view.
- If you use Spaces or Rooms, you can create a schedule that contains all your model elements and their Rooms or Spaces. You can then select all the elements in a certain room (such as the plenum) and hide them. This is probably the fastest way to hide multiple objects with certainty.
- You can add a custom parameter to all objects, such as "VR-Visible" and then select all of the items that do not have this property in a schedule and hide the item in your view.
- Detail levels should be set to Medium. Coarse will remove the structural columns and Fine will add rounded edges to the columns, adding way too much geometry. I would consider doing this especially for furniture and other assets that you will be re-using in the future. It may be worth contacting the furniture manufacturers about the need for geometric detail levels in their BIM families.
- You can use detail levels in Revit's family systems. Just make sure the Medium detail level will give you enough detail for VR and your other purposes.
- You can create Subcategories and control these with the Visibility Settings.
- You can create a custom View Visibility/Graphic override, great for turning off things like rebar.
- You can turn off Worksets.
- You can manually hide things.
- You can use selection sets to hide objects.
- You can make preset 3D plenum views to easily select plenum objects that are hidden and add them to your "hidden" selection sets.
Keep in mind that the biggest geometry offenders are curves - railings are usually the worst. It may be worth turning them off in fire escapes, depending on your VR presentation needs. Furniture and models downloaded from manufacturers are often over modeled. It is worth contacting the manufacturers to let them know of your needs or remodeling important families that you are likely to use repeatedly throughout the model or different projects. Keep in mind that simplifying the geometry makes for better VR and better Revit responsiveness, so you may see performance gains.
You could also model round railings as 12+ sided circumscribed polygons instead of circles and then go over it with detail lines for detail drawings. In the example below, the triangle count is dropped by almost 10 times. We suggest combining this with Revit's detail levels capabilities to get the best of both models.