This paper presents a method for the detection and the geo-localization of obstacle in outdoor environment. The proposed approach exploits a geographical 3D model managed by a 3D Geographical Information System (3D-GIS) and a video camera. An image processing module is developed to match synchronized real image and virtual image. The real image is provided by an on-board camera and gives the real view of the scene seen by the vehicle whereas the virtual image is provided by the 3D-GIS. A centimetric LRK GPS provides an estimation of the geo-position of the vehicle, which is used to localized the vehicle in the geographical 3D model. Obstacle(s) are then detected and tracked by comparison between the real image that contain the obstacle(s) and the virtual image where obstacle(s) are absent. The developed method permits also to compute the distance between the camera and obstacle(s), as well as the geo-position of these detected obstacles. In order to validate the computed distance, a 2D ladar (laser range scanner) is used. A necessary condition to complete the comparison is to calibrate the camera and the ladar together. Experimental results with real data are presented in the final section.