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PROFESSOR: --is that
for objects that

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look the same size
in the camera,

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the angle between
a line of sight

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along one edge of the
object and a line of sight

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along the other
edge of the object

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is always the same angle.

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[INAUDIBLE],, could you grab me
one of those big kick balls?

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This is useful, because if we
know that things in the camera

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look the same size they're
always the same angle, that

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allows us, like
you guys just did,

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to predict where we'd
need to put this in order

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for it to look the same size.

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All we have to do is extend
these lines out a little bit

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until the width
between the lines

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gets to be large enough
to accommodate the object.

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If you stand on your tiptoes and
look if I put the object there,

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well, obviously the
edges of the object

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are outside of my
lines of sight.

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Whoops.

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Uh-oh, could you pull that back?

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Whereas if I go
further back to right

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about here, if I extend
this line of sight that way

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and if I extend that line of
sight there, right about here

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the line of sight is going
to be about the same angle

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for this object.

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00:01:42,190 --> 00:01:45,780
So this is why astronomers and
people who do image science

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call this thing, this width
of the object in the image,

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00:01:50,910 --> 00:01:56,570
they actually call
it the angular width.

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It's the angular width,
because it's the angle

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that the object takes up.

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If we had a different
object that was larger,

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it would have a
different angular width.

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So we have this idea
of, in our case,

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we're not going to
call it the width

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of the object in
the image anymore,

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although that's what it is.

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00:02:20,090 --> 00:02:24,090
But we're going to call it the
angular width, because we're

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really not measuring a distance,
we're measuring an angle.

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00:02:28,104 --> 00:02:29,520
Because if we
measured a distance,

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we'd actually measure
the width of this

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00:02:31,145 --> 00:02:35,240
and we'd come up
with this column.