# Automatic Mobile Warning System against People with Elevated Body Temperature
###### Abstract
In these methods, the camera movement is most often used with proportional changes in the size of the observed object in the image or geometrical relationships in the scene, e.g., when moving away from the object, its size is reduced, and further objects move more slowly in the image [9]. These methods often require initial information on object size and camera parameters. In [13], the authors used a single camera to estimate distance to obstacles in the way of a train. In [14], a distance-assessment method using information about reference objects in the image was proposed. In this case, data about the location and size of the known object or  
Figure 1: FLIR One camera and connection to a smartphone [5]. known shape in the field of view helpedd in determining the distance. The method was used to control a robot. Another example of using a single camera is related to determining distance to vehicles [15]. Active distance measurement using additional ultrasonic sensors, lasers, or radars is a completely different approach [16]. In this case, information from the sensors is the basis for distance assessment. Systems of this type are very efficient, but their cost may be higher compared to image-analysis systems. To assess distance, images from two cameras can also be used (thermal and visible light). However, there is the problem of determining the correspondence between images. The authors in [17] used this technique to reconstruct models in 3D using a smartphone camera and the Flir One thermal camera. All the above-presented methods were used to determine or classify the distance to objects or vehicles. However, distance classification mechanisms can be extended and used to inform about an approaching human figure. This type of solutions may warn against a person with elevated body temperature. The use of stationary thermal cameras for the rapid detection of potentially sick people was proposed several years ago during the SARS outbreak [18; 19]. Systems of this type were installed at airports and stations, and allowed for detecting potentially sick people in a quick and noninvasive manner. In the current situation, with the rapid spread of the SARS-CoV-2 coronavirus [20], this type of mobile system could be used to alert the user of an approaching a person with elevated body temperature. This paper proposes the use of a mobile thermal camera to detect persons with elevated body temperature and estimate the approximate distance from them. After obtaining this information, the system informs the user that a person with elevated body temperature is approaching them, which may allow for taking preventive measures. In the available literature, it is difficult to find cases of directly determining the distance to the object using a thermal camera. On the basis of literature analysis, a distance-estimation method is proposed that is based on a single thermal camera using object tracking in subsequent frames of image sequences, and distance classification using machine-learning methods. The presented algorithm automatically and in real time analyzes images from the mobile thermal camera, detects and tracks a person with an elevated temperature, and reports the distance to them.