Aiming at the problems of complicated installation and low measurement efficiency of existing inclinometers in measuring the maximum pendulum angle of large observation cars, a swing angle measurement method that combines feature filtering and projection conversion is proposed in this paper. This method uses a combination of LiDAR and surveillance camera data to achieve non-contact, accurate measurement of the swing angle of a large observation vehicle. Firstly, the point cloud of the swing arm is selected by a directional feature filter. Then, the irregularly shaped point cloud is removed by a shape feature filter. Next, the point cloud is projected to a two-dimensional plane and the edge straight line is fitted by the least-squares method to solve the swing angle. Finally, the average absolute value of the angle measurement error of the method is 0.29°, and the maximum absolute value of the error is 0.45°, which is obtained by the equal scale model experiment. The experimental results show that the method can effectively improve the efficiency and ensure the accuracy of the measurement of the pendulum angle of the large observation car.