Caution! Google Earth for Drone Planning Uses True North, Not Magnetic

Are you planning a RPAS (Remotely Piloted Aircraft System) mission using Google Earth's powerful measurement and path tools? If so, there's a critical detail you must be aware of to ensure your flight operations are safe and accurate:

Google Earth provides headings in relation to True North, not Magnetic North.

Failing to account for this difference—the magnetic declination—can lead to significant navigation errors, especially on longer missions or in areas with high declination.

Understanding the Difference: True vs. Magnetic North

• True North (or Geographic North) is the fixed point representing the northern end of the Earth's axis of rotation. It's the stable, theoretical reference point for all globes and maps.

• Magnetic North is the point on the Earth's surface where the planet's magnetic field lines point vertically downward. This point is constantly moving and rarely aligns with True North.

Your drone's compass, the one used for onboard navigation and determining its current heading, is aligned with Magnetic North. The headings you derive from Google Earth, however, are referencing True North.

The angular difference between True North and Magnetic North is called Magnetic Declination. This value varies significantly depending on your geographic location and changes over time.

The Conversion: From True Heading to Magnetic Heading

To accurately program your drone's flight path, you need to convert the True Heading (TH) you get from Google Earth into a Magnetic Heading (MH).

The general formula is:

MH = TH - Declination

• East Declination (The magnetic field is East of True North): The declination value is considered positive (+). You will subtract it from the True Heading to get the Magnetic Heading.

MH = TH - (+ Declination}

• West Declination (The magnetic field is West of True North): The declination value is considered negative (-). You will add it to the True Heading to get the Magnetic Heading.

MH = TH - (- Declination} implies MH = TH + Declination

Example:

1. You measure a path on Google Earth and get a True Heading (TH) of 270 degrees

2. You find that your mission area has a Magnetic Declination of 15 degrees West (a negative value).

3. Calculation: MH = 270 - (-15) = 270 + 15 = 285 degrees

4. Result: To fly that path, you should command a Magnetic Heading (MH) of 285 degrees

How to Find the Magnetic Declination

You should never rely on outdated or generalized declination values. You need the current declination for your specific mission area.

1. NOAA's National Centers for Environmental Information (NCEI): Their online magnetic declination calculator is one of the most reliable and up-to-date resources. You input the latitude/longitude of your mission area and the current date to get the precise declination.

2. Aeronautical Charts: For manned aviation (and often used by RPAS operators), VFR (Visual Flight Rules) Sectional Charts have isogonic lines that show the declination for a given area.

Key Takeaway for Mission Planning

Before you upload any route to your drone's flight controller, make the conversion!

Always remember:

Google Earth (True Heading)  —> Declination Calculation __> Drone Flight Controller (Magnetic Heading)

References

• Federal Aviation Administration (FAA): Pilot's Handbook of Aeronautical Knowledge, Chapter 14: Navigation. (Provides the fundamental concepts of True and Magnetic North in aviation.)

• National Oceanic and Atmospheric Administration (NOAA) / NCEI: World Magnetic Model (WMM) and Magnetic Field Calculators. (The source for accurate, up-to-date declination data.)

Magnetic Declination Across Canada (East to West)

Summary of Declination Trend

As you move westward across Canada, the magnetic declination transitions from being strongly West (subtracted from True North) in the Atlantic provinces to being strongly East (added to True North) in the Prairie and Pacific provinces.

The declination is currently negative (West) for cities from St. John's to Toronto, and positive (East) for cities from Winnipeg to Victoria. This transition occurs somewhere in Central Ontario/Western Manitoba.

Crucial RPAS Note: For mission planning, always use a specific, current date and the exact coordinates of your operations to obtain the most accurate magnetic declination from an official source like the NOAA/NCEI calculator, as these values change over time.