What does the boom angle of a crane refer to?

The boom angle of a crane refers to the angle between the boom and the horizontal ground. This measurement is crucial, as it helps determine the crane's lifting capacity and stability when operating. A correct understanding of the boom angle is essential for ensuring safe lifting operations. When the boom is angled upward from the horizontal, it directly affects the radius from the center of rotation of the crane and the load it can lift.

Since the other options provide angles relating to vertical positions, load alignment, or the operator's viewpoint, they don't accurately reflect the term "boom angle" as used in crane operations. The focus on the angle to the horizontal is what makes this definition significant in crane operation safety and efficiency.