1. A spray painting system for spray painting external walls of building, the system comprising:a gondola for hanging on a motor driven pulley system, wherein the motor driven pulley system comprises a pair of rails and a set of motors located at roof-top end of the pulley system; wherein the pair of rails are disposed in a horizontal plane on the roof-top, and the hanging gondola is disposed in a vertical plane in parallel to an external wall; thereby, when the set of motors drives the pulley system along the pair of rails in the horizontal plane, the gondola operationally traverses in the vertical plane along the pair of rails along a linear distance of the rails for a painting process to be carried out; wherein the gondola comprises a controlling motor of the pulley system that hoists and lowers the gondola in parallel to the external wall of the building to be painted, wherein the controlling motor is located within the gondola;
a six-axis robotic arm, coupled with a 3D camera, and a spray nozzle on its end effector, the six-axis robotic arm is seated on the gondola for carrying out spray painting on the external walls;
wherein the 3D camera mounted on the robotic arm operationally scans a wall area to be painted; and
a software program adapted for receiving the scanned results from the 3D camera and calculating the trajectory path of the spray painting's motion for the robotic arm.