From the course: 3ds Max 2025 Essential Training

Specifying units of measurement - 3ds Max Tutorial

From the course: 3ds Max 2025 Essential Training

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Specifying units of measurement

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- [Instructor] Layout is the process of setting up a 3D scene. The most important principle of layout is scale. The size of the world and the size of objects is super important. You won't get good results if the objects are not scaled properly. Every model that you import into a layout should use the same scale convention. It is very bad practice indeed, to model objects at random sizes and then try to scale them in your layout phase. That is a recipe for disaster. Before you even begin to model anything, you need to establish your scale convention and stick to it. If you have a scene open and you don't know the scale of objects, here's one way to figure that out. You can just build a box. I'll go to the Create panel to standard primitives box and I'll set the length to 36 and the creation method to cube, click Create and I get a cube that's 36 units on a side. I can go over to the Modify panel, and we'll see length, width, and height are reading out at 36. Maybe asking 36 what? Well, these are generic units. What is a generic unit? It's an internal system unit. It determines the accuracy of calculations in space. By default, a system unit is actually an inch, but Max allows us to display and enter distance values in other units such as centimeters or feet, regardless of the system units. Let's look into our unit setup. In the customized menu, choose Units Setup and we see the display unit scale is set to generic units. I can demonstrate that these are actually currently inches by simply switching the display unit scale over to US Standard. And from the pull down list, make sure it says decimal inches. I'll click Okay. And over in the Modify panel, we now see length, width, and height read out in inches. We've got a double quote at the end of each one of those numeric fields indicating inches. The values didn't change because a generic unit is an inch by default. And of course, the size of the object didn't change. We just changed the units of measurement. So okay, so that's how generic units work. You'll almost always want to explicitly set your display units per scene instead of using generic units. Let's go back into that dialogue, customize Units Setup, and let's look a little bit more deeply at US Standard units. You can choose feet or inches. If you choose feet with either fractional or decimal inches, then you additionally have the ability to determine how 3ds Max will interpret keystrokes. If I set it to feet and decimal inches, then the default units field is available, and if I choose feet, then when I type in a one, 3ds Max will interpret that as one foot. If I choose inches and then I type in a one, 3ds Max will interpret that as one inch. To demonstrate, I'll click Okay. And then over here in the parameters, we see three feet and zero inches for each one of those fields. If I go to the height and type in a six and a zero and press enter, 3ds Max interpreted that as 60 inches, which equals five feet. Okay, I can undo that, just right-click in the view and press Control Z. I'm going to use the metric system with centimeters throughout most of this course, so that the scenes will be compatible with international audiences. If you're an architect or interior designer working in the USA, you'll probably use US Standard. But otherwise, I'd recommend using the metric system. I'll go back into Customize Units Setup and choose Metric with centimeters as the display unit scale. When I click Okay, back over in the parameters, we see 91.44 centimeters instead of three feet or 36 inches. Again, we just changed the units of measurement. We did not change the size of the object. However, there is a way to adjust the scale of the entire world and the accuracy of spatial calculations by changing the system units. We'll go back into Customize Units Setup, click the big button at the top, System Units Setup, and that launches a child window where we can choose a different convention for the system unit scale. Here, we can set the internal accuracy of 3ds Max. We can interpret a system unit as any size and that will scale the world up or down accordingly. You may need to do this if you're modeling a very small or a very large scene. If you wanted to model a very large object such as a planet, then you would need to change the system unit scale, or else build a miniature version of the planet. The system unit scale is a very powerful feature. Most 3D programs don't even have this ability. When you change this, you alter the absolute size of objects in the world. If I set the system unit scale to meters, then that will scale the entire world. Now if you look over at our Modify panel, we see values in the thousands of centimeters. I've scaled up my entire world by a very large factor. Nothing changed in the viewport, but the entire world is now being interpreted at a different scale. A 3D scene is not really infinite in size and it is also not infinitely accurate. If you try to model something too large or too small or too far away from the origin, you'll get round-off errors. Points on your model can collapse and corrupt the model or objects may not render. Usually, you want the system unit scale at the default of inches because that's a good compromise for scenes that are built relative to the scale of the human body. You can model objects that are very small, like fractions of a millimeter in size, and you can also model objects that are very large, on the scale of kilometers. So the system unit scale is really only applicable in two situations. The first is when you need to model a very large or very small scene and you can't cheat by modeling a miniature. A more common application of system unit scale is for compatibility with other applications. For example, maybe you need to export to a game engine that needs system units set to something else. A common option is centimeters. And by the way, if you set Max to centimeters, it will be directly compatible with Maya and you will not need to scale anything in the import export process. However, I do recommend that you leave this at inches unless you have a compelling reason to change it. If you set it to inches, then you're compatible with all the defaults in 3ds Max. Okay, so with that set to inches, I'll click Okay, and this is the setting I'm going to use mostly throughout the course, system units set to inches, but display units set to metric with centimeters. Alright, so one last point. If you're going to change the system unit scale, it is best practice to change it before you begin modeling. If you change the system unit scale in the middle of a project, you may experience those round-off errors that I mentioned. And that's how to set up display units and system units.

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