To calculate a missing bearing when you know the interior and exterior coordinates of a location, you're essentially looking for the angle or direction from one point to another. Bearings are typically measured clockwise from the north direction, and there are various ways to calculate them depending on the method you're using. Here's the step-by-step approach:

Steps to calculate a missing bearing:

1. Convert the known coordinates into a suitable format: Ensure that your coordinates are in decimal degrees (e.g., latitude and longitude). If your coordinates are in degrees, minutes, and seconds (DMS), convert them to decimal degrees.

2. Determine the change in coordinates: Calculate the difference in latitude (Δlat) and longitude (Δlon) between the two points.

   • $\Delta lat = lat_2 - lat_1$
   • $\Delta lon = lon_2 - lon_1$

3. Use the formula to calculate the initial bearing: The formula for calculating the bearing between two points on the Earth’s surface (using the haversine method or trigonometric functions) is:

   $\theta = \text{atan2}\left( \sin(\Delta lon) \cdot \cos(lat_2), \cos(lat_1) \cdot \sin(lat_2) - \sin(lat_1) \cdot \cos(lat_2) \cdot \cos(\Delta lon) \right)$

   Here:

   • $\theta$ is the bearing in radians.
   • $\text{atan2}(y, x)$ is a function that calculates the angle in radians between the positive x-axis and the point given by the coordinates (x, y).

4. Convert the bearing to degrees: Bearings are typically expressed in degrees, so convert the result from radians to degrees:

   $\theta_{\text{degrees}} = \theta \times \frac{180}{\pi}$

5. Adjust the bearing to a compass angle: Bearings are measured clockwise from north (0°). If the calculated bearing is negative, add 360° to get the final bearing:

   $\text{Bearing} = (\theta_{\text{degrees}} + 360) \mod 360$

This result will give you the bearing from the first point to the second point.

Example:

Assume you have two points with coordinates:

• Point A: $lat_1 = 51.5074° N, lon_1 = 0.1278° W$ (London)
• Point B: $lat_2 = 40.7128° N, lon_2 = -74.0060° W$ (New York)

Following the steps above will give you the bearing from London to New York.

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Would you like me to go through a specific example with your given coordinates, or do you have more details? Feel free to share!

Five follow-up questions:

1. Do you need help with converting DMS (degrees, minutes, and seconds) to decimal degrees?
2. Would you like to understand how to use haversine for distance as well?
3. Are you interested in bearings relative to magnetic north rather than true north?
4. Do you need clarification on the atan2 function and its significance?
5. Would you like me to show how to use a calculator or a programming tool for this computation?

Tip:

Bearings are usually measured from north, but if you're working with maps, make sure you're aware of the difference between true north, grid north, and magnetic north, as it may affect your calculations.