Rotating Line Method

The rotating line method is a method of obtaining the top and front views of a line, when its true length and true inclinations are given.
When a view of a line is parallel to the XY line, its other view will be in true length and at true inclination.

By following the procedure mentioned previously, in the reverse order, the true length and true inclinations of a line from the given set of top and front views can be found.

Determination of true length and true inclinations of a line.

• Draw the top view ab and the front view a’b’ as given
• Rotation of the top view:  With center a and radius ab rotate the top view to the new position ab1 to make it parallel to the XY line. Since ab1 is parallel to the XY line, its corresponding front view will be in true length and at true inclination.
• Rotation of the front view: With center a’ and radius a’b’ rotate the front view to the new position a’b2′ parallel to the XY line.  Since a’b2‘ is  parallel to the XY line,  its corresponding top view will be in true length and at true inclination. In this position, the line will be parallel to HP and inclined at f to VP. Through b draw the locus of B in the top view. Project b2′ to get b2, in the top view. Connect ab2 which will be in true length and true inclination f which the given line AB makes with VP.