- [Narrator] The display unit scale setting
that we saw in the previous movie
allows us to change the system of measurement,
but it doesn't actually change the size of objects.
It doesn't scale the world
but there is a way it has change the scale of the world
and the accuracy of spatial calculations.
By changing the system units, let's take a look.
I've got this one cubic meter box here,
select it go over to the modified panel to show you
length, width and height are set to one meter.
My display units are set to metric and meters.
Now let's go into the customized menu to units setup.
The big button at the top is labeled System Unit Setup
click on that and it launches a child window
System Unit Setup.
And here we can set the internal accuracy of 3ds Max.
We can set a system unit to any size
and that will effectively scale the world up or down.
An example of when you might need to do this
is if your modeling a very large or a very small scene.
If you wanted to model something super large, like a planet
and measure it at unity scale or one to one scale
then you might want to change
the System Unit Scale value here
to something like kilometers.
The other way that you could approach this
is to build a miniature version of your planet
which is not actually measured at one to one scale.
So this is important.
3ds Max actually allows you to change the system unit scale.
Some other programs, namely Maya don't have this ability.
You can't change the System Unit Scale.
And the only option you have is to build a miniature
but in Max, you can actually change the absolute size
of system units and that'll affect the objects
that are already in the World.
If I set the System Unit Scale here to meters
then look what happened over here in the modified panel,
the viewport didn't change
but now that box is considered to be
almost 40 meters on a side,
effectively the entire World is now being interpreted
at a different scale.
Usually you do want the system unit set to inches
and that's the default because it's a good compromise
for scenes that are built relative
to the scale of the human body.
If system units are set to inches
you can model objects that are very small
like fractions of a millimeter.
You can also model objects that are very large
on the scale of kilometers.
Below this is an origin slider that allows us
to check the accuracy of calculations at various distances.
So not to get too technical
but a 3d scene is not really infinite.
It seems infinite, but it's not.
We do don't have infinite calculation capabilities
in any computer.
So it's not an infinite size.
And it's also not infinitely accurate.
As we get farther away from the origin
or the center of the World,
the calculation accuracy goes down.
And as we drag this slider, we're testing that accuracy
at different distances away from the origin.
This black mark over here indicates the distance
at one system unit away.
So if we drag the slider over there
we're testing the accuracy
at one system unit away from the origin.
The number down here resulting accuracy
indicates the smallest distance or the smallest area
of space that can be resolved at that distance.
Higher numbers are less accurate
at a given distance 3ds Max can't determine the difference
between two points.
If they're closer together than this threshold
we want that value to be as low as possible.
So if we have the slider up here very far away
from the origin, we have less accuracy
but if we're very close to the origin
then we're getting higher accuracy.
So that should give you a clue as to best practices.
Simply having objects far away
from the origin is a bad idea.
You're asking for problems such as round off errors.
Points on a model can actually collapse
and corrupt your shape or object
may not render at all and so on.
The system units setup is really only applicable
in two situations.
The first as I said is when you need to model
something very large or very small
and keep it at unity scale
and you don't want to build a miniature
maybe you're not able to build a miniature
a more common application actually
is for compatibility with other applications.
For example, maybe you need to export
to a game engine that needs system units
since something other than inches, that's really common.
Or if you want to send something over into Maya
without it being scaled,
then you would need to set your System Units Scale
to centimeters.
I don't recommend that you change the System Units Scale
unless you have a compelling reason to do so.
You would want to leave it at inches
unless there's some reason to change it.
So I'll set this back to inches.
I'll go ahead and click, okay.
And exit out of that dialogue
and exit out of the unit setup as well.
We didn't actually change anything.
One last point
if you're going to change the System Unit Scale
it's 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.
It's how to use the System Unit Scale
to set the accuracy of internal calculations
and to maximize compatibility with other applications.