MGRS Tools iPhone App

Here is a tool designed to help out with four of the more time-consuming tasks associated with military land navigation. The app is free to download from the iOS App Store, supporting GPS location and Distance-Azimuth calculations. If you like what you see, then use In-App Purchase to enable the other three modules Grid4Target, Intersection and Resection.

Unlike most other navigation tools for the iPhone, MGRS Tools is designed to be fully functional without a data connection. This makes the application more useful to our service members when operating in remote training areas or deployed overseas in combat operations.

Technical Aspects

• All MGRS locations use the WGS84 map datum.
• Distance-Azimuth calculations – FROM and TO locations must be greater than 500 meters apart.
• Intersection/Resection – Azimuths from the Observers locations when using Intersection (or back azimuths from Known Points when using Resection) are validated to insure that they intersect prior to calculating a solution.
• As a safety measure, any previously calculated solution is automatically cleared whenever a value is modified in the respective module. Any change in G-M Angle will automatically clear all previously calculated solutions.

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Setting the G-M Angle

The difference between true north and magnetic north, often referred to as the “G-M Angle”, is critical when conducting land navigation. This difference varies widely based on your location, and will directly affect the accuracy of solutions provided by this program.

• To access the G-M Angle page, click on “Settings” (if using the free version) or the “GM Angle” menu button (if using the Pro version).
• Insure the G-M Angle is set to the appropriate value. When finished setting the G-M Angle, click on “Save”.

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Distance-Azimuth

One of the most common tasks of military land navigation is calculating the distance and azimuth between two locations. MGRS Tools can save you time by automating this process.

• Input the FROM grid location by using either the GPS button to the right of the input field, or manually enter the grid using the keyboard.
• Input the TO grid location. As with the FROM grid, this can be entered using the GPS button (useful if you are providing someone with directions to your location), or this can be manually entered using the keyboard.
• Click on “Calculate”. The distance (in meters), and both Grid Azimuth and Magnetic Azimuth will be displayed in the solution box.

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Additional Features Available with In-App Purchase

While the ability to calculate Distance-Azimuth is fully functional in the free version, you can enable even more features with a single In-App Purchase:

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Grid4Target

Determine the grid for an observed target by following these steps:

• Enter the observer’s grid by pressing the GPS button to the right of the “Obs Grid” text field, or by clicking in the text field and using the keyboard.
• Enter the distance to the target. You can change the scale of the distance by pressing the button next to the “Distance” text field. The distance scale will cycle between “meters”, “KM”, “yards” and “miles”.
• Enter the magnetic azimuth to target. (MGRS Tools will automatically compensate for the difference between true north and magnetic north when determine the target location.) The magnetic azimuth can be in degrees or mils. To change the angular scale, simply press on the button to the right of the “Mag Azimuth” text field.
• Press “Calculate” to see the MGRS location of the observed target.

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Intersection

This module can be used when you have to Observation Posts (OPs) in fixed locations, and they both call in the magnetic azimuths to an observed target or event. This can also be used when on patrol by logging your position and azimuth to a stationary target (say, a building), and then moving to another location and entering the second location and azimuth.

To determine the grid location for an observed target using Intersection, just follow these steps:

• Enter the location of the first Observation Point by using either the GPS button to the right of the text field, or clicking in the text field and manually entering the location.
• Enter the magnetic azimuth to the observed target for Observation Point 1.
• Enter the location of the second Observation Point by using either the GPS button to the right of the text field, or clicking in the text field and manually entering the location.
• Enter the magnetic azimuth to the observed target for Observation Point 2.
• Press “Calculate” to see the MGRS grid location of the observed target. As a safety measure to prevent invalid results, azimuths will be validated to make sure they intersect prior to calculating the solution.

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Resection

Resection is used to determine the grid location for an observer that can identify two known points. Obviously, if you have this program, you can simply press the GPS button in any module to determine your current location. However, one possible scenario for using this module would be when you have radio contact with someone else who only has a compass. By having them provide you with two prominent points, and the azimuths to those points, you can determine their MGRS grid location.

To use Resection to determine an MGRS location, follow these steps:

• Enter the location of the first Known Point by using either the GPS button to the right of the text field (if you are at one of the known points visible to the observer), or clicking in the text field and manually entering the location.
• Enter the Observer’s magnetic azimuth to Known Point 1.
• Enter the location of the second Known Point. As with nearly all location fields, you can do this by using either the GPS button to the right of the text field, or clicking in the text field and manually entering the location.
• Enter the Observer’s magnetic azimuth to Known Point 2.
• Press “Calculate” to see the MGRS grid location of the Observer. As a safety measure to prevent invalid results, back-azimuths to the observer will be validated to make sure they intersect prior to calculating the solution.

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Orientation Locking

MGRS Tools was written for service members to use while out in the field. One of the easiest ways to enable quick access to your tools from Military Pro is to wear your iPhone or iPod in an exercise band on your forearm. This allows quick access the your apps while on the move (or even in the prone position).

The Pro version of MGRS Tools enables you to set orientation locking from the G-M Angle page. Simply turn on or off the orientations you want to use. Landscape orientation is the best option when wearing the device on your forearm.