ObjectiveVideo monitoring system is widely used in forest fire detection, in which forest fire position is calculated by cameral coordinate and PTZ parameters such as azimuth, pitch angle. There are three common methods for forest fire positioning, i.e. single-point positioning, double-point positioning and multipoint positioning. At present, some researches have been carried out to enhance the expression of three-dimensional scene by mapping between video images and three-dimensional virtual terrain based on the ray tracing algorithm, which can be applied to smoke and fire positioning in the image. Nowadays, many forest fire monitoring systems have been built up for monitoring, decision-making and fire-fighting, which integrating the hardware and software system including video surveillance, PTZ camera and GIS system. This paper subjects to take advantage of the terrain analysis in GIS and image process technique to match video images to virtual terrain, puts forward a smoke and fire positioning method based on image, and evaluates the positioning accuracy.

MethodFirstly, a virtual terrain was generated from DEM by the camera location and view of field, and forest fire image was mapped to the virtual terrain based on the principle of terrain profile matching. Each pixel in the image can be projected to an area on DEM as the positioning area, and the information of the positioning area can be calculated and analyzed, such as the coordinate, Euclidean distance, azimuth, angle of pitch of center point, shape, area, visibility, the number of crossing the valley of the area.Then the accuracy information of the area was analyzed and a decision was made according to visibility and number of crossing the valley, which divided the area into two classes, one can be positioned accurately and the other can not be positioned accurately.

ResultIn this paper, Jiulong Mountain Nature Reserve in Beijing was selected as the test area, and the proposed positioning method of smoke and fire was verified. The results showed that this method can provide location information in detail, and gave an evaluation about the positioning accuracy, which can help to locate the fire source quickly and make a quick response.

ConclusionIn this paper, the positioning method of smoke and fire makes full use of the matching relationship between virtual terrain and video images, provides abundant location information for forest fire fighting. This method performs better than the traditional PTZ positioning which depends on hardware performance specifications, its positioning accuracy is only related to the resolution of image and the matching accuracy between virtual terrain and real image. At the same time, the method is also applicable to images taken by mobile devices such as smart phones. Locating the coordinates of the shooting point, we can realize the positioning of the targets in the image, which has important significance for the image-based positioning analysis.