why the hokuyo lidar show the walls curve and not straight

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i have a hokuyo lidar ubg-04lx-f01 and i generate a pointcloud with laserscan. I move the LIDAR up and down i get register. the problem is when i put the PCL into a 3D point cloud processing software (cloud compare), the points that represent walls looks like a curve and not straight like is it. Anybody can help with this one pls. the problem could be in the code ? i have a part of the code

self.tabla_datos = PointCloud()
angles_azimuth = np.linspace(msg.angle_min, msg.angle_max, len(msg.ranges))
self.coord_x = msg.ranges * np.cos(angles_azimuth) * np.sin(np.deg2rad(self.angles_elevation))
self.coord_y = msg.ranges * np.sin(angles_azimuth) * np.sin(np.deg2rad(self.angles_elevation))
self.coord_z = msg.ranges * np.cos(np.deg2rad(self.angles_elevation))

for i in range(0, len(self.coord_z)):
    point = Point32()
    point.x = self.coord_x[i]
    point.y = self.coord_y[i]
    point.z = self.coord_z[i]
    self.tabla_datos.points.append(point)