Camera projection matrix is always the same

Question

I wrote a simple python script to render a scene from different points of view. For each rendered image i also need to save the projection matrix of the camera that took the picture.

I try to get the projection matrix with calc_matrix_camera(), but it seems that even if i change the location/orientation of the camera the resulting matrix is always the same. Is the matrix returned by calc_matrix_camera an intrinsic matrix? Is it premultiplied with the extrinsic matrix? Can anyone point me to the right direction?

I am running the script via command line.

Here's the code i use to get the projection matrix:

for step in range(0, steps):
        radians = np.radians(step * (angle / steps))
        subject.location = (250 * np.cos(radians), 250 * np.sin(radians) , 150)
        look_at(subject, (0,0,100))
        dg = bpy.context.evaluated_depsgraph_get() 
        dg.update()
        projection_mat = bpy.context.scene.camera.calc_matrix_camera(
                dg,       #bpy.context.view_layer.depsgraph,#
                x=bpy.context.scene.render.resolution_x,
                y=bpy.context.scene.render.resolution_y,
                scale_x=bpy.context.scene.render.pixel_aspect_x,
                scale_y=bpy.context.scene.render.pixel_aspect_y
                )