Shows two methods to find the true length of a line

1. Original position
New position
(parallel to
frontal plane)
Rotate
the line
End point of true
length will lie on
the same
horizontal plane
True length (TL)
of the line
TV
FV
METHOD 2
Auxiliary view method:
Draw an auxiliary view of the line with
the reference line parallel to the line
in one of the principle planes
The length of the auxiliary view of the
line gives the True Length (TL) of the
line
METHOD 1
Rotation method:
Rotate the line in one of the principle views
such that it is parallel to the other principle
planes
Project the new position of the line onto a
straight line through the end point of the
original line in the other view
The length of the projection is the True
Length (TL)
This line represents the plane on which
the end of the line rotates
a
b
a’
b’
a1
b1
FINDING TRUE LENGTH OF
A LINE (SHOWN IN RED)
x1
y1
x y
b1’
b1”
True length
(TL) of the
line

2. Original position
New position
(parallel to
frontal plane)
Rotate
the line
End point of true
length will lie on
the same
horizontal line
True length (TL)
of the line
TV
FV
Draw the true length of
a line by rotation or
auxiliary view method
The angle made by the
true length with the
reference axis is the
TRUE INCLINATION of
the line with the
adjacent plane
In this case it is α with
the top plane
This line represents the plane on which
the end of the line rotates
a
b
a’
b’
a1
b1
FINDING TRUE INCLINATION OF
A LINE
x1
y1
x y
b1’
b1”
True length (TL) of the
line
α
α
True inclination of the line with
horizontal plane

3. a’
b’
a1
a
b2, a2
Point view of line
TV
FV
x
x1
x2
y1
y2
y
b
b1
True length
PRIMARY AUXILIARY
VIEW
An Auxiliary View of the
Point View of a line shows
always the True Length of
the line
b2
b3
a2
a3
Auxiliary view of Point
view of the line