ZBrushCentral

Help me understand the tool scale in ZB

ZBrush Usage Questions
#1

Even though the OBJ exported from a certain tool is normal sized, it seems like inside ZB it behaves different.

I notice that when I switch from the suspicious tool to another. The other tool turns tiny. Or the other way around, when I work with normal (or what I believe is normal) sized tools and then switch to the suspicious one, the camera is on the character-tool’s feet. So I need to zoom out.

So how do these things work?
I noticed this thing when comparing different tools; the suspicous tool has export scale 1, while all the others have around 100 or above.

Thanks

#2

Scale is a tough subject when going between programs because there are no standards for what the numbers mean in the .obj format. For example, 1.0 can mean 1mm or 1cm or 1m or 1km without difficulty. Zbrush tries to compensate for this on import/export with a scale factor it attaches to the ztl (which you can see on the export options when importing objects.)

If you plan to keep multiple objects in zbrush for a while, note the scale factor of what you want to be your master object (such as the primary figure.) By appending any other tools scaled to it as subtools, they can then all be exported at the same scale as long that scale factor stays consistent.

I frequently tool->deformations->unify to rescale objects to a good, natural scale for zbrush, rescale them to each other, and then correct the scale after export. Not the most automatic system in the world, but a system where I’m in control for some of those troublesome import/export issues between apps.

-K

#3

Hello again Kerwin and thanks.

If I understood your explanation correct, the scale is for ZB only and “only” important when more tools are interacting with eachother.
Also, if I understood it correctly the export scale value should have another equivalent somewhere else, like for import.
Because it seems like no matter what the export scale is, when I reimport in eg Maya or Max the size is correct - probably because of what you said before 1 is 1 cm, or m or whatever is set in the 3d application.

I went to check out the Unify button. It scaled down that huge and scaled character to match the other tools I had appended as subtools.

But does it mean that ZB scales all this just virtually when using unify?

Last but not least; What would happen if I played with the export scale values by hand?

#4

Unify will scale the tool to match the canvas for calculation purposes. This (more or less) puts the tool/object in a scale where you will end up with the least rounding errors for Zbrush’s internal calculations. Zbrush uses many optimizations to achieve its ability of handling such vast number of polygons at once, so things that are too small or too large potentially interfere with these calculations (causing rounding errors.)

The other tools you had were probably already close to “unity space” so it was just the abnormally large one that was out of step.

When you fiddle the with the export scale factor by hand, you are essentially changing a multiplier that is scaled against the Zbrush’s internal numbers when the object is export. Bigger numbers will make the object seem “bigger” in your other applications, while numbers less than 1 (but greater than zero) will make the object smaller. The other offset numbers are added the coordinate system to shift the object in the X,Y, or Z direction respectively. This tends to only be important when discussing object symmetry.

#5

Thanks for your info. I think I understand more

About that tool that was very big; you think it could be because I had zoomed out too much so that ZB scaled in a way that made it much bigger?