function volume = cylinder_volume_3d ( p1, p2, r )

%% CYLINDER_VOLUME_3D determines the volume of a cylinder in 3D.
%
%  Discussion:
%
%    A (right) (finite) cylinder in 3D is the set of points
%    contained on or inside a circle of radius R, whose center
%    lies along the line segment from point P1 to P2, and whose
%    plane is perpendicular to that line segment.
%
%  Modified:
%
%    11 August 2005
%
%  Author:
%
%    John Burkardt
%
%  Parameters:
%
%    Input, real P1(3), P2(3), the first and last points
%    on the axis line of the cylinder.
%
%    Input, real R, the radius of the cylinder.
%
%    Output, real VOLUME, the volume of the cylinder.
%
  dim_num = 3;

  h = r8vec_distance ( dim_num, p1, p2 );

  volume = pi * r * r * h;