Abstract: Offline foreign objects are a common defect in overhead transmission lines,which can affect the normal operation of transmission lines. If these offline foreign objects cannot be detected and removed in a timely manner,they may cause serious power grid accidents and endanger the safe and stable operation of the power grid. To address this,an unmanned aerial vehicle （UAV） ranging device based on image processing technology was developed and designed. The high-definition camera of the ranging device collects images of the detection area,and the digital signal processor （DSP） is used to preprocess the collected images in real time. The virtual wireframe technology is used to mark the areas within the image range,and the threshold changes within the area are monitored at all times. The distance between the overhead transmission line and the offline foreign object is obtained by calculating the occupancy ratio. Through on-site application,the UAV ranging device can accurately locate and measure offline foreign objects,providing a powerful tool for the investigation of offline foreign objects.

Key words: offline foreign objects, unmanned aerial vehicle （UAV） ranging device, digital signal processor （DSP）, virtual wireframe technology