>> Okay. This lecture is
on orthographic projection and multiviews.
The orthographic projection has this prefix ortho,
which means perpendicular
as in orthogonal planes or orthogonal lines.
They're perpendicular to each other.
Orthographic projection refers to a system drawing views
of a given object by projecting points onto planes
in the direction that's perpendicular to the planes.
So you have projection lines that represent the line of sight
and the line of sight are perpendicular
to the projection plane.
As a result, the projection lines are also perpendicular
to projection planes.
And this gives rise what's called multiviews.
Multi means many.
So these multiviews are two-dimensional views
of an object projected upon two or more planes
of the projection using orthographic
projection techniques.
Here's an illustration of an orthographic projection
that result into a view.
We have a 3-D object here in the back, okay.
And we place a projection plane.
In this case, it's in front of the object.
So it's called a frontal projection plane.
And then, we look at the features such as vertices
and edges of the given 3-D object and project them
into the projection plane perpendicular
to the plane itself and they would trace an image here,
as shown here.
This little image on the projection plane
in this particular image is called front view
because it's projected onto the frontal plane.
Now if you do this to two or more projection planes,
you'll get multiviews.
Here's an example of a collection of multiview
for exactly the same object here but this time projected
into three projection planes: one that gives you the top view,
another that gives you the front view,
another that gives you right side view.
And notice the placement of these principal views.
Front view is in the middle.
The right side is always to the right of the front.
and the top is always above the front.
To illustrate this even further,
let's consider this three-dimensional object here,
okay.
We're going to use what's called a glass box model,
meaning we're going to put this three-dimensional object inside
a glass box.
You see that thin outline of a line that looks like an aquarium
or a glass box that's slightly bigger
than the overall dimensions of the object.
So you put the object inside the glass box, okay,
such that the faces of the glass box are parallel to some
of the major surfaces of a plane of the 3-D object.
And then, the next thing you do is you project, okay,
the features through orthographic projection
of the object into each of three projections planes:
the top horizontal plane, the frontal plane,
and the right profile plane.
So that's the orthographic projection part of it.
And then, what you do is you remove the object
and then you cut the glass box along this edge right here,
along the edges.
And then, you open up the box, okay, and then fold it
to obtain the views, okay.
This technique is called the third-angle projection that's
used in the US.
For in the top is going to be placed directly
above the front view and the ride-side view directly
to the right of the front.
So here's another demonstration of the glass box as it unfolds
after we cut it and open it.
There we go.
And take note, this is now your top view.
This is your front view.
And this is your ride-side view.
And notice the perfect alignment of features in the top.
Between the top and the front, the front and the ride-side view
and also between the right-side view and the front view
if we fold it back, okay.
So I'll talk some more about the multiviews, okay.
We use common projection planes,
also known as principal projection planes,
as we saw the frontal plane giving you the front view,
the horizontal plane, the top horizontal plane giving you the
top view, and the right profile plane p giving you the right
side view.
And then, we cut the glass box open to get the three views.
But in addition to these three,
sometimes you also have the bottom of the box
as your projection plane,
the rear of the box, or the left side.
So you may have six of them, six views.
Dimensions are necessary in order to define the object.
So we have a three-dimensional object.
A three-dimensional object has three dimensions obviously
and the dimensions are the height,
the width, and the depth, okay.
And as I mentioned earlier, okay, these dimensions,
the height dimensions for instance,
should be aligned perfectly
between the two corresponding views, the width dimensions
between the top and the front view,
as well as the depth dimensions
between the top and the right views.
If you notice some of the lines that we saw earlier
in our multiviews are dashed, okay.
They represent hidden edges of the object.
Okay, here's an illustration of the alignment
of the dimensions in a multiview.
Here's the width.
And as you can see, the width dimension is shared
between the top and the front.
Here's the height.
It's showing in both the front and the right-side view.
And this is the depth, okay, and it's shown in the top view
and the ride-side view.
And the way you check the alignment is
by using what's called a miter line.
This 45-degree line here is a miter line to make sure
that the depth, as it's shown in the right side view,
is exactly the same as the depth shown in the top view.
Vertical parallel projections lines, right,
should correspond features in the top and the right-side view.
Horizontal ones should correspond alignment of features
between the front and the right side.
How do you select which one is the front view?
The front view seems to be the center view.
As a general rule, you want the front view to be as descriptive
as possible representing the most natural position
of use of the object.
And as a general rule, okay, you select width
as the longest dimensions,
which should be shown in the front view.
Also, for it to be most descriptive,
you want to make sure that the front view has
as few hidden lines as possible, hidden features as possible.
Here's an illustration.
This is the natural position of this 3-D object.
And we select this as the front view, the number one,
because it's descriptive of the overall contour.
The number two, it also captures this biggest dimension of width.
And here is an illustration of the glass box model again,
this time showing the six rather than the three principal views.
So you have the front view, the right side view, top view.
And then, we can also project into the left plane here.
The left profile plane will give you the left-side view.
You can project down into the bottom plane, down here.
That will give you the bottom view.
And there's a plane back here you can project it
to give you the rear view.
And here's an illustration of how you open your glass box
if you want to show the six principal views.
Here's the front.
But the way you add the three other views are...
the left should be to the left of the front,
the bottom is below the front, and then the rear is actually
to the left of the left.
And notice the alignment of the corresponding dimensions.
Okay, selecting this as the front makes sense,
because it has the widest dimension here.
Representing the right here is better
than representing the left because it's more descriptive,
because this is shown as a solid line
from the right-side view here.
Displaying here would be solid.
On the other hand, from the left, it becomes hidden.
So it's better to use the right compared to the left,
at least for this object.
In addition to solid lines that represent visible lines
of the object and the hidden lines,
that we also have seen represented by dashed lines
for the edges of the object, are currently hidden.
We also have centerlines and we talked about this
in week one lecture in the alphabet of lines.
Centerlines are generally represented as long, short,
sequence of long, short, long, short dashes.
And they're used to indicate the positions of centers
of all circles and arcs.
And we have other types of lines: dimension lines,
extension or witness lines.
Phantom, section, and cutting planes,
we'll talk about when we get to sectional view.
Here's an illustration of hidden lines to show
that this plane here, as viewed from the front, is not visible,
but the line inside the edges, one on this side and one
to this side, are still there, but they're hidden, okay.
Same thing here.
The limiting element
of the cylindrical hole will be represented as hidden lines,
both in the top and the front view.
Now notice also the center lines here, long, short, long, long,
short, long, okay, representing the position
of both the cylindrical hole and the semi-circular part here.
And here also, long, short, long, long short,
long in both directions.
What this slide is indicating is
that when you have a smooth transition from a curved surface
into a plane, there is no line that separates those two
because the transition is smooth.
On the other hand, in a case like this,
there should be a solid line here, right,
representing this edge here or this skinny long plane here
as viewed from the front.
Line precedence, this is what you will follow in terms of what
and when to represent,
which type of line whenever you have two
or more lines coincidently in the same position.
When one type of lines falls in line with a different type
of line, draw the line that is most important based
on precedence.
So object lines take precedence over any other type of line.
Now between hidden line and centerlines,
hidden lines have precedence over centerlines.
So if you have a position wherein hidden
and centerlines should both be there,
forget about the centerline.
Hidden lines take precedence.
In sectioning, as you will see later on,
cutting plane lines take precedence also
over centerlines.
Different type of planes.
We talked about this.
Indication of the relative orientations with respect
to your projection plane.
A normal plane is one that is parallel to one
of the three principal projection planes,
either frontal, horizontal, or profile plane.
And as a result, this normal plane will be seen
in only one view as true size and the other views,
it will just be an edge or an edge view.
An inclined plane is tilted with respect
to two principal projection planes.
And as a result, it can be seen in two views
but not in its true size.
On the other hand, an oblique plane is one that is tilted
with respect to all the principal projection planes.
And as a result, will be visible but not
in its true size in those three views.
Here's an illustration here.
The blue one, A, is parallel to the frontal plane.
And as a result, you see it in its true size
and shape in the front.
B is also normal and it's parallel
to the top horizontal plane,
therefore it's showing its true size in the top.
But if you look at the front, it's on its edge as well
as the right side view.
C is another normal plane.
It's parallel to the profile plane.
You see the true size here.
However, C is only shown on this edge here, in the front,
and also on its edge, the top view.
D is an example of an inclined line.
As you can see, it's shown as planes in two views,
top and the horizontal and the top and the right explains
that therefore the sizes of D here, shown in the views,
are actually smaller than the actual true size in D.
And D is shown as an edge
and that they're viewed at the front.
An example of an oblique plane is E. And as you can see,
E is shown as the planes end, as the plane in the three views.
But none of the three views is showing its true size and shape.
Sometimes when we're trying to visualize 3-D objects,
in order to determine how to represent them in views,
it might be useful to label planes, plane a, plane b,
plane g, for instance,
so you can easily locate them in the views.
In others, okay, it might even be better to represent lines
and label line and vertices.
For instance here, point three, four, five,
six actually represent plane C. Here's another illustration
of labeling of surfaces and planes.
Here's an example of labeling vertices and lines.
For labs number 4A and 4B, you will be given a 3-D object,
okay, and you will be asked to sketch on paper
and pencil the three principal views: top, front, right.
You will have a second part wherein you're going
to be creating multiviews in AutoCAD.
And when you do that in AutoCAD, okay,
it's best to group entities together into layers.
All the object lines should go to layers.
Now layers-- What is a layer?
A layer is a way of grouping entities, entities meaning lines
and arcs and objects, together.
If you imagine seeing an architect using tracing paper,
tracing paper is kind of transparent,
an architect may use many different papers
for different parts of the plans.
So for instance, you might have a layer or a paper
for electrical, another one for the walls,
another one for furniture, and so on and so forth.
So you can view each layer individually if you want
or you can overlay the layers together if you want
to see how they fit well connected to each other.
And that's the whole idea behind layers also.
So you will have a layer for all the object lines,
for all the hidden lines, for all the section lines
and hatching associated with sectional views,
texts and dimension, and maybe for title border.
So for instance, if I just want to see all the object lines
without the other details, I'll turn this on
and turn off the rest of them.
And then, the next step is after you've created the layers,
you create basic construction lines representing the overall
outline of the front, top, and right-side views, okay,
using third angle projection.
Again, front and the middle, right to the right of the front,
and top above the front, okay.
And make sure that you observe appropriate spacing
between the views.
Then, you start creating construction lines in order
to locate height dimensions between the front view
and the right-side view.
Those will be horizontal construction lines
and then vertical construction lines to align dimensions
of width between the front and the top.
And then you use the miter line in order
to transfer depth measurements, okay, between the top view
and the right-side view.
And then from there, it might be a good idea to start locating
on the planes and start representing those normal planes
with object lines, okay and then work on the inclined
and then work on the oblique planes.
Once you have all the following lines figured out,
you can now start looking for hidden lines
and then add other types of lines, such as centerlines
for all circles and arcs.
Whenever you have a coincident of line,
make sure that you can follow our rules
for precedence of lines.
And then optional, add dimensions and texts,
at least for some of the labs.
Dimensions are and texts are optional.