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Understanding 3ds Max Units – Part 01 – Project Scale

In this tutorial, you learn to set and control units in 3ds Max. Doing so, you gain a better understanding of the differences between Display and System Units. This is an area I’m always asked about as many users find it confusing. There is an important distinction to be made between Display and System Units in 3ds Max, and we will explore them together in this tutorial. Start 3ds Max and make sure you are in a new, blank scene. Use the Reset function if you need to. Use the Customize menu to access the Units Setup dialog. This gives you access to the Display Units, which by default, are set to Generic. This is not session-based. It means that if you change your setup to metric or imperial, that option would be retained as you reset or restart 3ds Max again.

Since we are here, let’s tackle Display Units first. These are the easier ones to understand. As mentioned a second ago, the default is set to Generic units. Generic Units work fine in many situations but don’t necessarily give you a “Real-World” sense of scale. Often, you would rely on Display Units set in metric or imperial formats. What makes Display Units easy to understand and use is that you can change them at any time in your project. Case in point, say you set your Display Units to Feet and Inches, and then create a box that has a dimension of 3 feet on each side.

At any time, you can go back to the Display Units dialog, change the setup to meters for example, and the parameters of the box update, to show properly converted edge dimensions of 0.914m What is mostly significant here is that you can switch back and forth without affecting the integrity of the scene. This makes Display Units very safe and convenient if and when you need to work in units that feel more comfortable to you. System Units on the other hand, are a totally different matterů You typically set System Units at the beginning of a new project, and you do not change them after that. If you do, it will likely mess up the work you have already started. See what happens to the box if you were to change System Units at this time. In this movie, I’m switching System Units from the default Inches setup to the Meters setup. The box, which was initially set to 3 feet in size (or a little less than 1m) is now 36m in each direction.

You would then need to scale it down or edit its parameters to bring it to the correct size. It’s easy enough with one object but more complicated if you had dozens or hundreds of objects in the scene. So, let us explore a bit more how to work with System Units and how to set them up. The main thing to remember about System Units is that they determine the overall scale of your project. This means that the nature of the project you are starting dictates the System Units you need to establish. You do not set System Units the same way if you are designing a cell phone than if you are designing an aircraft carrier. Put simply, if your design is small in scope like a cell phone or a child’s toy, then your System Units should be small as well. This ensures you can work in smaller detail, where a fraction of an inch or a millimeter matters.

If you are designing a condo or a building, you can still work in smaller System Units but it really depends on the level of detail you are after. Often, it is enough to set the System Units in Feet or Meters as your ultimate goal is visualization, and precision down to a fraction of an inch is therefore not always necessary. This is certainly true for larger architectural designs such as stadiums or arenas. In fact, when it comes to architectural designs and mostly to interoperability with Autodesk Revit models or other FBX files, I would suggest making it a habit to set System Units in Feet, regardless of the Display Units you are comfortable with. More on that in a momentů If your designs are much larger in scope and span over miles or kilometers, then you would set your System Units accordingly.

This can be useful when designing highways or large expanse areas. These basic guidelines are made obvious when you start creating objects in a new scene. Set the Display Units to Feet and Inches and the System Units to Inches and then reset 3ds Max. Create a box in the center of the world. Make it about a quarter or a third of the grid in length and width; you don’t need great accuracy here. Because System Units are set to Inches, the box is roughly about 3 feet in each direction. Now set the System Units to Feet and reset 3ds Max one more time. Create the same box one more time, and note that it is closer to 40 feet in size this time around. The same box that could have been used to model a small object a second ago is now suddenly as big as a house. Now try it with System Units set to Miles: The box is now insanely big, over 200000 feet in each direction. Unless you are working on huge expanses of terrain, you may want to avoid setting System Units to such a large scale.

So keep that in mind, and set your System Units to match the general scale of the project you are starting. Another thing to look out for is the placement of objects in a scene. Typically, when you are creating objects in 3ds Max, you create them around the center of the world. This is the way it should be, as creating or moving objects too far from [0,0,0] tends to result in various problems. The further you are from the center of the world and the less accuracy you have. In fact, the System Units dialog has a slider that calculates the accuracy loss when moving away from the origin. These three UI controls do not affect the units setup, they are just meant as an accuracy calculator as you move away from the center of the world. You can reset the slider position with a right click. Some of the accuracy problems relate to viewport clipping or unexpected flipping of normals.

Camera POVs can also be affected by unexpected twitches. To demonstrate, open the file named Garage_CAM.max Adopt the file’s scale at this time to open it as it was designed. It shows a very simple structure of a car garage and an animated camera constrained to a spline. Playback the camera animation, all seems to be working properly with the camera smoothly moving into the garage. In the top view, select all objects except the camera. You’re about to move the entire scene, but the camera is already constrained to the path, so it’ll move automatically. Zoom back quite extensively, and then move the selection far away from the center of the scene. The camera viewport doesn’t change since all objects are still in the same position relative to one another. They are just globally in a different location in the scene, far away from the origin. Playback the camera view once again and notice the twitching in the animation, and the flipping of the normals on the garage door.

Chances are you won’t see this problem if your work is done in 3ds Max, as you would naturally create objects near the center. However, this problem can easily happen when you merge or import models done with third-party applications. This means you may need to move models closer to the origin to prevent these problems from happening. In the next movie, we take a look at importing models that were built in different scales, and how to make them fit your project better.

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