What defines plate line capacity in mechanical excavation?

The correct choice refers to the bucket volume when following the bucket's outline, which accurately reflects how plate line capacity is assessed in mechanical excavation. This measure focuses on the actual dimensions and shape of the bucket, providing a realistic assessment of how much material the bucket can effectively hold and transport.

By assessing the capacity based on the bucket's outline, factors such as the curvature and design of the bucket are taken into account, ensuring that the measurement aligns with practical excavation and lifting scenarios. This assessment is pivotal because the outward shape and design will affect how much material can properly fill the bucket without spilling or being underloaded.

In contrast, other options present different aspects of excavation equipment. While the overall size of the excavation equipment is important, it does not specifically define the capacity of the bucket itself. The theoretical maximum volume capacity of the bucket is an idealized figure that may not represent real-world conditions such as material density and cohesion. Finally, the actual volume of material after loading the bucket can vary significantly based on how the material behaves when being excavated, making it less reliable as a measure of capacity. Therefore, focusing on the outline of the bucket provides a clear and consistent definition of plate line capacity in mechanical excavation.