Join Ryan Kittleson for an in-depth discussion in this video Fixing scale problems in zbrush, part of ZBrush: Tips & Tricks.
- Z brush is notorious for messing up the scales of objects, especially when you need the scale to work right with other software. This is because, most of its features are tuned to work best on models that are about one to four units in the longest directions. That's why everything is scaled by default to be two units wide. Now, z brush does some calculations under the hood to compensate for this but in the end, it causes more problems than it solves. In this video, we'll take a peek under the hood and see some ways of dealing with the issue.
Okay, so we've got a basic sphere here that you might get if you just append it as a sub tool and let's take a look at how big it is. Let's go under geometry and size and you can see it is two units in x, y and z. Now let's import a file that we know exactly how big it is. Go to import, okay, under the exercise files, go into the scale problems folder for this video and let's open up this file and I know that this file is 10 millimeters in the longest dimension so let's go ahead and open this up.
So what we see according to my custom grid, is that it's actually more like, two units right here. So that's definitely not right, we go and look in our size here now, you can see, two units in the z axis and then, 1.5 roughly in y and one in x. Now let's see what happens if we measure it with a transpose tool, so I'm going to click on any of the transpose tools here, rotate around to a side view and I'll just draw out a new manipulator here from the back side to the front side and you can see that it's pretty much 10 units.
So, why are we getting a scale of two units in the size, but 10 units with the transpose tool and that is because, z brush has resized our model when we imported it, to be two units in the longest dimension. Let's scroll down to export and what you can see here is a scale compensation unit, so what basically happened is, z brush divided the model by a certain amount basically so it was 10 units to begin with, z brush scaled that down to two units so that's a factor of five.
This scale setting right here, is a fudge factor basically, to sort of compensate for that change in scale. Now for the most part, this works under the hood. If we export this model, it will multiply the units of two by this scale and it'll end up being the same size it was when it was exported or before it was exported and that's what it's doing with the transpose manipulator, it's multiplying everything by this scale amount. So what would normally be two, is getting multiplied by five and that's why we get 10 up here in the units.
However, not everything in z brush respects this scale factor. For example, if we're trying to extrude thickness on an object and we go into geometry and we go into edged loop and let's say, we want to use panel loops here to add thickness to this object. Let's go ahead and set some of these settings, zero polish, zero bevel, negative elevation, one loop that's fine and let's say we want to give this a thickness of .1 and then we'll go ahead and do panel loops.
The thickness will actually come out to the wrong amount because it's not taking into account that scale factor. Go ahead, ctrl Z to undo that, what I usually like to do is bypass the scale factor so that everything is the actual units that it should be. So let's get out of transpose tool, go into draw mode and what I like to do is, go back to export and set this scale to one.
Now, what I'll do is I go to sub tool and if I reimport the sub tool, it should come in at the correct scale. Okay, now you can see that if we go to geometry in size, you can see that scale is coming in correct now, 10 units in the longest dimension. Go to export, you can see scale of one. You look at this from a side view, we go back to transpose, drag out, see how long that is and it is the correct measurement.
Now obviously this is a bit more complicated than I would really like it to be, I would like z brush to just not mess with the units at all and just make sure everything is just exactly what it should be without any fudge factors that would be really nice and I use the size sliders, I actually move this into my custom interface so I can see these sizes all the time because when I'm working with objects for 3D printing, I want to be able to just look at a glance and see exactly how big an object is in every dimension.
But if I let z brush use that scale factor, this number is not going to match up with the actual size of the object. For this reason, I also like to have the export scale, I like to bring this into my custom interface, so I can always see at a glance if that's set to one, if it's set to something else, then I know that z brush has messed with the scale and I can change it accordingly. Okay, so this tip was a little bit cumbersome but unfortunately, that's what you have to deal with when z brush itself, makes things cumbersome under the hood.
But hopefully, once you figured out how this works, you won't have quite so many problems with scale in the future.
Skill Level Intermediate
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