# Analysis of Drone Flight Stability for Building a Korean Urban Air Traffic (K-UAM) Delivery System
## 3 Flight Data Coordinate System  
The coordinate system for analyzing drone flight data is generally a combination of the Global Coordinate System and the Body Coordinate System. This allows for accurate interpretation of the drone's position, attitude (Euler angles), speed, etc. The Global Coordinate System is a coordinate system that considers the Earth as a three-dimensional ellipsoid and indicates the location on the Earth. The Earth is considered an ellipsoid and a point on the Earth's surface is represented by latitude and longitude, and the unit is degree. The drone's GPS data are expressed as latitude, longitude, and altitude, and the definitions of each term are as follows:  
- Latitude: The angle formed by the vertical line of a given point on the Earth's surface and the equator. - Longitude: The angle formed by the prime meridian and the meridian drawn from the South Pole to the North Pole through a given point on the Earth's surface. - Latitude: A line connecting points of the same latitude. - Longitude: A vertical line on the Earth's surface that connects the North Pole and the South Pole at the shortest distance, also called a meridian. - Prime meridian: A line with a longitude of 0\({}^{\circ}\) that serves as the standard for longitude. Passes through the Greenwich Observatory in England. The GPS receives latitude, longitude, and altitude information from satellites. Since the Earth is round, we can easily express this on a map by converting it to the UTM (Universal Transverse Mercator) coordinate system and expressing where it is on the map. The UTM coordinate system is one of the geographic coordinate systems that converts the Earth's surface into a flat surface. The UTM system divides the Earth into several zones and applies a flat coordinate system to each zone, providing high accuracy. It is mainly used in fields such as map making, navigation systems, and GPS. In Figure 3, the UTM coordinate system divides the Earth into 60 vertical zones. Each zone covers a 6-degree longitude range and separates the Northern and Southern Hemispheres. For example, Zone 1 covers longitudes from 180\({}^{\circ}\)W to 174\({}^{\circ}\)W, and this zone is divided into the Northern and Southern hemispheres. The zone numbers increase eastward. Each UTM zone is defined by the central meridian of that zone. The central meridian is not a meridian with longitude 0, but rather the central longitude of each zone. The coordinate system is set based on this longitude, minimizing distortion at that longitude. The UTM coordinate system is expressed as Easting and Northing, and Easting is a value from 0 to 1,000,000, and the reference starts at the Central meridian. The Central meridian is usually set to 500,000 m, so that it is expressed only in positive values. Northing is calculated starting at 0 and increasing towards the North pole, and in the Southern hemisphere it increases towards the South pole. In the Northern hemisphere it starts at 0, and in the Southern hemisphere it starts at 10,000,000 m and increases towards the South. However, since the projection calculation is performed in the same way as the UTM system but with the reference point at the equator, a lot of distortion occurs in South Korea. The UTM-K coordinate system was created as a countermeasure for this, and it is a case where only the origin and added values are applied differently from the UTM coordinate system, as shown in Figure 4 and Table 1. The reference origin is set as the intersection of longitude 127.5\({}^{\circ}\) and latitude 38\({}^{\circ}\), and the coordinates are expressed by adding a value of 1,000,000 m in the X-axis and 2,000,000 m in the Y-axis directions. The previous TM coordinate system had four origins, making it difficult to unify the coordinate system, but the UTM-K coordinate system uses one origin and unifies the entire country into one coordinate system.