Calculate the Height of Triangle ABC: Perpendicular Altitude Construction

To determine the height of triangle $\triangle ABC$, we need to identify the line segment that extends from a vertex and meets the opposite side at a right angle.

Given the diagram of the triangle, we consider the base $AC$ and need to find the line segment from vertex $B$ to this base.

From the diagram, segment $BD$ is drawn from $B$ and intersects the line $AC$ (or its extension) perpendicularly. Therefore, it represents the height of the triangle $\triangle ABC$.

Thus, the height of $\triangle ABC$ is segment $BD$.