- [Instructor] In the last movie
we saw some unexpected results that can occur
with grid snapping in 3D.
If we have the select and move tool active
and we're snapping to 3D grid points,
the cursor will actually snap to the construction plane
that's visible in the current viewport.
So for example, if we go to the top view
and select some thing like this pergola cross beam
and move it around
it will instantly move down to an elevation of zero
because it's snapping to the construction plane
in the top view which is the X, Y plane of the world.
So we don't want that.
Let's learn how to work around it.
I'll undo that with Control+Z.
There are two work arounds for this.
We can either use 2.5D snap mode
or we can enable access constraints in 3D mode.
Let's look at 2.5D mode first.
So let's check in on our snap settings
first of all right click on the snap button
and in the home grid tab,
I've got a grid spacing of five centimeter
and major grid lines every five times 10 centimeters
or every 50 centimeters.
And in the snap tabs,
we're only snapping two grid points or grid intersections.
Let's close that dialogue and let's go into 2.5D snap mode.
Hold down the snap button
and you'll get a fly out and choose 2.5D.
And then if we move around in the top viewport
we get the result that we want.
We're only snapping in X and Y
and the object is not being sent down
to the construction plane or Z elevation of zero.
This mode moves the snap cursor in the 2D space
of the view port also known as the picture plane.
So to give you a little bit of background information,
rendering, which is the display of the 3D scene,
is the projection of that scene
into the flat 2D space of the image.
In this case, of viewport.
2.5D mode snaps the cursor
to the screen projection of something.
It doesn't snap to the thing itself.
That means for example,
when we move an object around in the top view,
we're snapping to grid intersection points in world X and Y
but we're not snapping to the X Y construction plane itself.
In an ortho view, in 2.5D mode
the snap tool doesn't change the value of the third axis.
It only changes the values of the axis shown here
in the axis tripod in the lower left.
That indicates the orientation
of the world coordinate system or the world grid.
We see X and Y here, X points to the right,
Y points towards the top of the screen.
And Z is just the letter Z,
we don't actually see an axis.
There's no axis line visible because Z is pointing
towards and away from our current viewpoint.
So we're basically looking straight down
and that Z axis is pointed towards us.
When we snap in 2.5D mode,
we're snapping in these two dimensions,
X and Y, in the top view,
but not in the third dimension, which is Z in the top view.
The upshot is the snap cursor maintains
a constant elevation if we move an object in 2.5D
in the top view.
All right, I'll undo that movement with Control+Z,
go back a few times, send that back where it was.
The other way to work around the issues with 3D snap
is by enabling axis constraints.
Let's go back to 3D snap mode
and let's test this out with default settings.
If we go over here and click on the Y axis
of the move gizmo and drag,
we would expect that we're only going to move in Y.
But that is not the case,
you can see that not only are we moving in X
but we've also sent the object back to
a Z elevation of zero.
That's quite odd when you move an object
with snaps turned off and you click on a single axis,
the object will only move in that axis.
But if snaps are turned on and you click on a single axis,
the default behavior is
there's no constraining that movement to that axis.
Axis constraints are turned off.
Well, let's enable them.
I'll undo that with Control+Z.
Right click on the snap button once again,
go into the grid and snap settings dialogue
to the options tab.
And at the bottom, you'll see translation.
And turn on the checkbox labeled, enable access constraints.
Turn that on, close the dialogue
and now we can test this.
Click on that Y axis and drag.
And you'll see, even though I move my cursor way over here,
I'm not moving the object in the X axis.
I'm only moving in Y
and you can see in the left view, additionally,
we haven't changed the elevation.
Okay, I'll undo that with Control+Z.
And if I wanted to move in X and Y
I could just click on the bracket on the move gizmo
and I'm moving in X and Y but again, not in Z.
So I'll undo that with Control+Z.
So I really recommend this,
axis constraints should be on by default.
I have no idea why it's disabled by default.
But it's super useful.
So enable axis constraints
and you can work in 3D mode,
you don't need to worry about 2D mode necessarily.
Okay, so now that we figured out how to use snaps properly,
we can go ahead and make some duplicates
of these pergola cross beams.
So I'll go ahead and drag a selection rectangle
around all of these.
And as we saw previously, we can make duplicates
by holding down the Shift key
and then transforming some selection.
So hold down Shift,
click on the Y axis of the move gizmo and drag down.
And once I've started dragging, I can release the Shift key.
I don't want to keep holding that down
and just position that where I want it
and I can observe the results in that left view as well.
And just set that so it's centered over the other columns,
release the mouse, we get the clone options dialogue.
We do want these to be instances.
They'll all be identical.
If we make a change to one, it will change all of them.
And it will be very efficient
in terms of memory consumption.
Go ahead and click okay.
All right, I also want another set of these
and that'll give me a chance to illustrate
what might be an issue.
Let me dolly back here in the perspective view.
Control+ alt and middle mouse and pan with a middle mouse.
I want another set of these pergola cross beams over here.
All right, so I'll pan over here in my top viewport.
But let's say for the sake of argument,
I didn't pan over far enough.
And the area that I want to snap to is not visible
in the viewport and that can be a problem.
It might not even be possible
for you to frame the view in advance
so that the thing that you want to copy
and the place that you want to copy it to
are both visible at the same time.
But I'll show you how we'll work around.
So here's the issue.
Let's say I've selected all these
and I want to duplicate them.
I'll hold down, Shift and click on the Y axis
of the move gizmo and then drag,
I can release the Shift key.
I don't want to keep holding that down.
And if I move this down far enough
my cursor will exit out of that viewport.
And once I've gone beyond the frame of that viewport
then there's nothing for my cursor to snap to.
So now I've got a problem and you might think
that you could just move it down here
and then move it again.
But actually if you go down here
and you're no longer snapping
and then you release the mouse,
you're going to end up dropping those objects
in some random location.
Okay, so here's what you can do.
You can start that movement,
still hold down the left mouse button
but also pan at the same time, this is pretty clever.
Hold down the middle mouse button
even though you're still in the process of cloning.
Hold down middle mouse and then drag
to reposition your viewport
and then release the middle mouse button
and still holding down the left mouse button,
you can drag and then position that
where you want it to be.
Finally release the mouse button,
once again, we want these to be instances
so I'll just click okay.
All right, I've got three sets of pergola cross beams
very precisely positioned using interactive snaps.
We've learned how to tame the snap tool
either by using 2.5D mode
or by enabling access constraints in 3D mode,
which is my preferred method.