## 2 Distance Measurement Module Development  
### Vehicle Detection Module Analysis  
The vehicle detection module acquires information using LiDAR sensors at two measuring points in the laser for the vehicle detection and the velocity calculation and transmits the information to the ground control part. The acquired information is essential information for detecting the vehicle and determining the velocity. The vehicle detection module is necessary to detect the driving vehicle, change the angle for each sensor, check the sensor arrangement and transmit data. The sensor angle change and the sensor placement determine vehicle velocity for two points on the road.  
Figure 3 is a connection diagram of the ground control part and the drone vehicle detection part. The drone vehicle detection part is composed of VDM, DIAM, camera and storage medium. The VDM creates raw sensor information for the vehicle detection and velocity calculation in the measurement range. The VDM collects the detection sensor information of two measuring points to calculate the vehicle velocity and transmits it to DIAM. The collected sensor information is important data for driving the vehicle detection and the velocity calculation. The VDM functions for detecting the driving vehicle are as follows:  
* detection of the driving vehicle distance between two measuring points;
* change of LiDAR sensor angle to measuring point distance;
* check the LiDAR sensor placement;
* the function of transmitting and processing the collected raw data.  
The VDM requires two LiDAR sensors to generate raw data for detecting the vehicle in each lane and a laser indicator to check the location of the LiDAR sensor projecting. The VDM communicates with the DIAM using three universal asynchronous receiver transmitters (UARTs).  
The VDM and DIAM of the vehicle detection part transmit data and control signals using serial communication and the camera and DIAM transmit information using high-definition multimedia interface (HDMI) communication. The 915 MHz radio frequency (RF) communication is used transmit control signals and data between the drone vehicle detection part and the ground control part. The LiDAR sensor front (LSF) and LiDAR sensor rear (LSR) are front/rear LiDAR sensors at the road's vehicle measurement point. The VDM is a device for detecting the driving vehicle and requires one VDM in one lane.  
Figure 3: Vehicle information detection system.  
Three VDMs are required to detect all vehicles driving in three lanes and one VDM is equipped with two LiDAR sensors. Vehicle information and the VDM status collected from the LiDAR sensor are transmitted to DIAM. The DIAM transmits start and stop signals and sampling rate to the VDM for the vehicle detection. The DIAM collects each lane's sensor distance information as measured by the camera and the VDM and stores the raw data in the vehicle detection and the storage medium (micro san disk memory). The DIAM transmits data to the ground control part the DIAA to calculate traffic volume and vehicle velocity in real-time. The ground part DMCA calculates the vehicle velocity using the DIAM data and the DIAA extracts the vehicle detection and the velocity using the raw information of the DIAM storage medium to extract more accurate traffic information.