>> This is a short lecture on the basics of 3D modeling.
We're going to talk about three basic facts of 3D CAD models.
The first type is what we call a wireframe model
and then a surface model, and then finally a solid model.
A wide frame model, the name imply,
uses wires to represent edges of actual objects.
You are only able to represent edges, surfaces,
or planes of the objects are not defined, only the boundaries
of the surface as represented by the edges.
As a result, the model is see through
and not useful for visualization.
We can see through the wires.
It has complete dimensional information,
meaning you can find locations of edges as well as vertices.
It contains no volume or surface.
It's easy to construct.
One advantage of it is it's really a simple extension
of what we've been doing so far.
We're creating two dimensional objects as it applies lines
and circles and arcs and polygons and borderlines.
But we're creating this-- 2D entities in 3D space.
And it's useful for planer, and useful planer
or single surfaces, but not for compound curved surfaces.
A planer or a single curved surface is one
in which all the points along the curve line
in the same plane.
An example of a compound curve is a helix,
because as you're going
around the helix it's also condensing in the z direction.
As an example, the y frame oil for cube is like the model--
a model constructed out of 12 coat hangers,
connected at their ends.
Four hangers for the top plane, four for the bottom plane,
and four for the forwarding lines connecting the top
and the bottom plane.
Surface model defines both surfaces and edges,
so it acts like advantage over y frame models
because it provides better visualization of 3D objects,
meaning surfaces that are closest--
closer to the observer will be--
will cover those that are behind.
However, it requires relatively tedious process,
because each surface must be constructed first
and then oriented relative to the rest
of the other surfaces in that model.
Auto CAD is not a complete surface modeler.
It only allows cleaner and single curved surfaces.
And the construction technique for a surface--
surface models in auto CAD is really very tedious.
And most of the time, wireframe models are used
to create the framework for building the surfaces.
So we're not going to do surface modeling in our labs
because we can actually go to directly to solid model,
which is the most complete in terms
of describing the 3D properties of the model.
It is really a computerized structurally actual object.
It contains all the geometric properties, the edges,
the surfaces, as well as a few features
of objects in their model.
It's has mass and volume, you can actually attach a density
to it in order to find other mass and volumetric properties
such as center of mass or centroid or moment of inertia.
And the construction techniques are usually simpler
than those of surface models.
That's why we're not even going to look at surface modeling.
For autoCAD, OK, the solid modeler
for auto CAD is called ACIS, which is hybrid modeler.
Hybrid because its combination of CSG,
constructive solid geometry.
It's a technique that involves combing primitive shapes.
We're going to call primitive such as boxes,
spheres, cylinders, wedges.
So all of that auto CAD comes with this big--
pretty much shapes, solid.
And we only use Boolean operations of union,
which is adding them together to subtract, taking one part
of the solid from another and then applying the intersections
in order to create more complicated solids.
That's nothing but combinations of simpler primitives.
And then the second part is boundary representation or BREP
in which a model is defined in terms of its edges
and surface boundaries on which side
of the surface the model lies.
Later on in the semester we're going to use SolidWorks,
which is I believe a better solid modeler than auto CAD.
It's based on what's called parametric modeling
or feature based modeling as we will talk about later.
Now, going back to auto CAD, in creating 3D models,
we're going to be using the work coordinates the same of WCAS,
which is attached to the ground or the real world.
And it's always available, cannot be erased.
And the x y plane is the horizontal n z represents the
height dimension as opposed to the UCS coordinates system
in which it's nothing but a temporary coordinate system,
used by or created by the user in order to aid in construction.
So it's used to simplify the equation of geometry
on a specific plane of surfaces of the object.
So for instance, if I'm going to create features
in the frontal plane, it would be easier
if my UCSS x y plane is on the front.
OK? Of my constructing features along an incline thing,
it might be easier to construct this feature if my UCS is
on the-- that inclining plane.
And there are many ways of defining the orientation,
and for this and as we will see in the lab.
You can use three points to define the origin, the x y--
the position of the x-axis and the position of the y-axis.
Of course, the z-axis will follow
from the right hand drawer.
Or you can use an existing UCS and just simply move the origin
or you can use an existing plane,
or you can also use UCS coordinate system
that are parallel to the front, top, left, right, bottom planes
and so on and so forth as we will see.
Before we start our construction we need to look
at the different ways on-- of how we can indicate positions
of points in 3D space.
So the first one is very effective in 3D.
It's by using interactive coordinates
or by simply using your objects map.
So if you already have existing geometry in 3D, you can go to--
you can smack to specific locations such as m point
of line, mid-points line, intersections of line and so on,
and centers of circles and so on and so forth.
You can also simply type absolute coordinates,
like given the x y z coordinates relative to your UCS.
So just we did it in 2D, if you don't--
if you only type two numbers, x comma y,
the z is assumed to be zero.
Just like we did for 2D,
a lot of times the relative coordinates system is
very effective.
So you give the x, y, and z coordinates
and put them out in front of it.
Meaning that the x, y, z coordinates are relatively
to the previous point or the last point
that you have indicated in your drawing.
And we can all see a cylindrical coordinates like we did before
in 2D by giving x as a distance, at distance
and angle comma the value.
We talked about the cylindrical coordinate system
and coefficient coordinate system 3D
and lecture number two I believe,
which is on engineering geometry.
So this might be a good time
to review though the cylindrical coordinates.
Then we have two distances, one radius, and one angle,
and then the z coordinate.
We can all see the spherical coordinates
where we only have one distance,
the radius of the sphere, and two angles.
The first angle is angle in the x y plane,
and the second one is angle from the x y plane.
And the last one is by using the two x distances.
And three, you give a distance and move the cursor
in the desired direction.
This is only effective if you're in ortho.
Orhto means that you can only move power level
to x, y-- one of the axis.
I think that's it.