WEBVTT

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>> This is a short lecture
on the basics of 3D modeling.

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We're going to talk about three
basic facts of 3D CAD models.

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The first type is what
we call a wireframe model

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and then a surface model, and
then finally a solid model.

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A wide frame model,
the name imply,

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uses wires to represent
edges of actual objects.

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You are only able to
represent edges, surfaces,

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or planes of the objects are
not defined, only the boundaries

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of the surface as
represented by the edges.

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As a result, the
model is see through

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and not useful for
visualization.

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We can see through the wires.

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It has complete dimensional
information,

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meaning you can find locations
of edges as well as vertices.

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It contains no volume
or surface.

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It's easy to construct.

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One advantage of it is it's
really a simple extension

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of what we've been doing so far.

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We're creating two dimensional
objects as it applies lines

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and circles and arcs and
polygons and borderlines.

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But we're creating this--
2D entities in 3D space.

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And it's useful for
planer, and useful planer

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or single surfaces, but not
for compound curved surfaces.

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A planer or a single
curved surface is one

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in which all the points
along the curve line

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in the same plane.

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An example of a compound
curve is a helix,

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because as you're going

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around the helix it's also
condensing in the z direction.

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As an example, the y frame oil
for cube is like the model--

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a model constructed
out of 12 coat hangers,

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connected at their ends.

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Four hangers for the top plane,
four for the bottom plane,

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and four for the forwarding
lines connecting the top

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and the bottom plane.

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Surface model defines
both surfaces and edges,

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so it acts like advantage
over y frame models

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because it provides better
visualization of 3D objects,

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meaning surfaces
that are closest--

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closer to the observer will be--

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will cover those
that are behind.

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However, it requires
relatively tedious process,

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because each surface
must be constructed first

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and then oriented
relative to the rest

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of the other surfaces
in that model.

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Auto CAD is not a
complete surface modeler.

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It only allows cleaner and
single curved surfaces.

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And the construction
technique for a surface--

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surface models in auto CAD
is really very tedious.

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And most of the time,
wireframe models are used

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to create the framework
for building the surfaces.

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So we're not going to do
surface modeling in our labs

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because we can actually go
to directly to solid model,

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which is the most
complete in terms

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of describing the 3D
properties of the model.

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It is really a computerized
structurally actual object.

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It contains all the geometric
properties, the edges,

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the surfaces, as well
as a few features

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of objects in their model.

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It's has mass and volume, you
can actually attach a density

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to it in order to find other
mass and volumetric properties

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such as center of mass or
centroid or moment of inertia.

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And the construction
techniques are usually simpler

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than those of surface models.

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That's why we're not even going
to look at surface modeling.

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For autoCAD, OK,
the solid modeler

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for auto CAD is called ACIS,
which is hybrid modeler.

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Hybrid because its
combination of CSG,

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constructive solid geometry.

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It's a technique that involves
combing primitive shapes.

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We're going to call
primitive such as boxes,

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spheres, cylinders, wedges.

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So all of that auto CAD
comes with this big--

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pretty much shapes, solid.

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And we only use Boolean
operations of union,

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which is adding them together
to subtract, taking one part

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of the solid from another and
then applying the intersections

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in order to create more
complicated solids.

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That's nothing but combinations
of simpler primitives.

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And then the second part is
boundary representation or BREP

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in which a model is defined
in terms of its edges

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and surface boundaries
on which side

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of the surface the model lies.

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Later on in the semester
we're going to use SolidWorks,

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which is I believe a better
solid modeler than auto CAD.

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It's based on what's
called parametric modeling

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or feature based modeling
as we will talk about later.

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Now, going back to auto
CAD, in creating 3D models,

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we're going to be using the work
coordinates the same of WCAS,

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which is attached to the
ground or the real world.

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And it's always available,
cannot be erased.

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And the x y plane is the
horizontal n z represents the

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height dimension as opposed
to the UCS coordinates system

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in which it's nothing but a
temporary coordinate system,

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used by or created by the user
in order to aid in construction.

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So it's used to simplify
the equation of geometry

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on a specific plane of
surfaces of the object.

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So for instance, if I'm
going to create features

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in the frontal plane,
it would be easier

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if my UCSS x y plane
is on the front.

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OK? Of my constructing
features along an incline thing,

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it might be easier to construct
this feature if my UCS is

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on the-- that inclining plane.

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And there are many ways of
defining the orientation,

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and for this and as we
will see in the lab.

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You can use three points to
define the origin, the x y--

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the position of the x-axis and
the position of the y-axis.

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Of course, the z-axis
will follow

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from the right hand drawer.

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Or you can use an existing UCS
and just simply move the origin

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or you can use an
existing plane,

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or you can also use
UCS coordinate system

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that are parallel to the front,
top, left, right, bottom planes

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and so on and so
forth as we will see.

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Before we start our
construction we need to look

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at the different ways on-- of
how we can indicate positions

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of points in 3D space.

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So the first one is
very effective in 3D.

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It's by using interactive
coordinates

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or by simply using
your objects map.

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So if you already have existing
geometry in 3D, you can go to--

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you can smack to specific
locations such as m point

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of line, mid-points line,
intersections of line and so on,

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and centers of circles
and so on and so forth.

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You can also simply type
absolute coordinates,

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like given the x y z coordinates
relative to your UCS.

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So just we did it in
2D, if you don't--

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if you only type two
numbers, x comma y,

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the z is assumed to be zero.

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Just like we did for 2D,

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a lot of times the relative
coordinates system is

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very effective.

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So you give the x,
y, and z coordinates

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and put them out in front of it.

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Meaning that the x, y, z
coordinates are relatively

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to the previous point
or the last point

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that you have indicated
in your drawing.

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And we can all see a cylindrical
coordinates like we did before

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in 2D by giving x as a
distance, at distance

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and angle comma the value.

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We talked about the
cylindrical coordinate system

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and coefficient coordinate
system 3D

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and lecture number
two I believe,

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which is on engineering
geometry.

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So this might be a good time

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to review though the
cylindrical coordinates.

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Then we have two distances,
one radius, and one angle,

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and then the z coordinate.

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We can all see the
spherical coordinates

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where we only have one distance,

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the radius of the
sphere, and two angles.

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The first angle is
angle in the x y plane,

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and the second one is
angle from the x y plane.

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And the last one is by
using the two x distances.

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And three, you give a
distance and move the cursor

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in the desired direction.

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This is only effective
if you're in ortho.

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Orhto means that you can
only move power level

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to x, y-- one of the axis.

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I think that's it.