In the previous bottle cap exercise you drew a
bottle cap from three different angles in perspective.
On the top and bottom views of the cap you could see
that the caps you drew had height, width and depth. But
it was a little hard to see the caps in perspective 
that the front part was closer to your eye than the back
part. That's because it's a pretty small, cylindrical
object, it doesn't have much depth. Now lets talk about
objects were you can see the depth  like rectangles
where the long end recedes away from your eye. How would
you draw that?
ONE POINT PERSPECTIVE exists when the subject
of the drawing is directly facing the picture plane. If
you stand on railroad tracks and look down them and they
vanish at the horizon  that's one point perspective. Or
stand next to a long chain link fence and see it go off
into the distance  you can mentally follow it until it
vanishes into the horizon. Using one point perspective
we can draw three dimensional looking boxes. And like
the bottle cap drawings we can depict the front, top
view and bottom view of a box.
First,
using a ruler, draw the horizon line on a new sheet of
paper. Mark the vanishing point in the middle of the
horizon line.
Next,
with the ruler draw 4 lines radiating downward out from
the bottom of the vanishing point. Make it look like a
triangle within a triangle (but don't draw the
horizontal bottom of the triangles).
Draw
a square with the corners of the square at the 4 lines
you drew. The top two square corners will intersect with
the outer triangle, and the bottom two square corners
will intersect with the inner triangle. (see the image
at right)
Now
draw the back of the box by drawing another horizontal
line above the top of the square. This line will go to
the edges of the outer triangle. Connect the line for
the back of the box to the square by darkening the lines
of the outer triangle.
If
you now erase the triangle lines you drew, you'll see
that you now have a three dimensional box where you can
see the top and the front face. You'll see that your box
appears to have real depth, more so than the bottle cap
drawings. This is because the vanishing point appears to
be almost right behind the box. Although this box looks
three dimensional, you can only see two sides of the box
 the top and front. In order to see three sides of a
box we'll have to use TWO point perspective.
TWO POINT PERSPECTIVE: Now you want to show the
corner of a box instead of it's front  That will need
two point perspective. Two point perspective has 2
vanishing points on the horizon line. And you'd draw
lines radiating out from both vanishing points. In real
life, if you see a fork in the road, the left fork would
disappear into the horizon at one vanishing point, and
the right fork would disappear at the other vanishing
point. In drawing, two point perspective is used to
depict three faces of an object, one point perspective
will only yield two faces of an object.
If you look at the two images of a toy car on the right
 the first is shown in one point perspective, and the
second is shown in two point perspective. You'll notice
that in the first you only see the front and top of the
car. In the second two point perspective image, you'll
notice that you can see the top, front and side of the
same car. These two images also show that you can depict
the same object in either one or two point perspective.
Let's
draw a simple box in two point perspective (the toy car
is too complicated to draw right now).
First
draw the horizon line horizontally across your paper.
Draw it a little lower than the middle of the paper.
Next
draw two vanishing points on the horizon line. If you
put them far apart, the box will be closer to the
horizon line and the angles won't be very extreme. If
you put the points close together, you'll get extreme
angles.
Now
draw the vanishing lines. Draw lines radiating out and
up above the horizon line from both points. Draw three
lines out from each point. Make a V shape first, then to
get the third line cut the V in half down the middle.
Draw the vanishing lines long enough so all the lines
intersect each other. So when you're done drawing the
vanishing lines you should have six of them  three from
each vanishing point.
Now
we'll draw what will be the corner of the box by drawing
a horizontal line at the point where the top two lines
intersect. Start the line there and draw it straight
down to the next intersecting vanishing lines.
Then
we'll draw the other two back edges of the box. The back
edges will start below the first horizontal line you
drew at the two intersecting vanishing lines. Draw the
two lines straight up until you come to the above
vanishing line.
Now
to fill in the box by connecting the three vertical
lines. You'll draw lines that connect the tops and
bottoms of the vertical lines by drawing along the
vanishing lines. The very back edge of the box will be
connected to the rest of the box by drawing lines along
the two innermost vanishing lines at the bottom.
The
last step is to erase the parts of the vanishing lines
that aren't used.
You
can color the resulting box if you'd like. Since we're
looking at the bottom of this box, you should color the
bottom plane of the box the darkest. This will signal to
your brain that the light source in the drawing is
coming from the top. In daylight, since the sun is
always above us, your brain is used to having shadows
being below objects, so to make your box look most
"normal", put the shadow on the bottom.
