An original mobile robot self-location technique in three dimensional environments is presented in this paper. This method solves the 3D location problem using a single colour camera on board the robot. A very simple pattern consisting of a few color points has been designed in order to achieve two main objectives. pose of the robot in the room and location of the robot in the building. Perspective projection analysis of the pattern is enough to obtain camera viewing parameters in the room coordinate system and color code analysis identifies the specific floor and room in the building. Our approach is being used for applications inside buildings Experimentation with a mobile robot, advantages and restriction of this technique are shown in the paper.