Magnetic Azimuth To Grid Azimuth

CONVERTING GRID AND MAGNETIC AZIMUTHS – HOW AND WHY

ESSENTIAL SKILLS: CONVERTING Filigree AND MAGNETIC AZIMUTHS – HOW AND WHY

repost from American Partisan

In the last post on Magnetic Declination, the bear on information technology has on azimuth/bearing accuracy was described. In this post, we're going to wait at the 'how and why' of converting grid (or map) azimuths/bearings to magnetic azimuths/bearings and vice versa.

Outset, a word about grid maps. They're not essential for 'shooting' an azimuth or bearing (from hear on out referred to as either a Filigree Azimuth (GAZ) or Magnetic Azimuth (MAZ)), just they are very, very useful is plotting (determining) positions on a map to within various levels of accuracy (read altitude from the actual object existence plotted). That'll exist covered in 1 of the next posts on this subject.

For your convenience, you lot can utilize a 'UTM' 'Universal Transverse Mercator' AKA USGS 7.five minute map. They'll either have 'tick' marks on them that you can utilise to provide your own grid (as I have done and commenters have suggested (Tip: Use very sparse map marking pens and don't use carmine ink – ruby disappears when using a red light) or complete grid lines. They're ok to use; they're typically in ane:24,000 scale, and you demand to ensure your map tools stand for in scale. More on that in the future. Personally, I prefer maps that use the MGRS (Armed forces Filigree Reference System) which is like to the UTM, but scaled in i:25,000 & ane:l,000, which is what I learned in during active duty. It'south a familiarity thing for me. YMMV. In either example, the listed Declination, or 'GM Bending' on the map (which may or may not be correct due to Magnetic North Pole motion) is for the center of the map, and depending on the what's under or on elevation of the surface, the Declination degree may be distorted during your trip. So, it'due south good to bank check the on line or other sources for up to the date declination numbers.

The simplest way bachelor to man correct now is to go a compass that has an declination adjustable feature, such as the Sunnto MC-3. Basically, one time you decide what your Magnetic Declination is, you lot simply use the provided tool, accommodate the declination reading to correspond with that number (either Due east or Westward) and use your compass on the map as well as when shooting your azimuth. No mathematical equation is necessary considering the compass itself has the declination already accounted for past your adjustment. In the jpg beneath, you lot can see the declination window at half dozen o'clock on the compass, or specifically, at Nil degrees. It'due south the fiddling black pincer looking thing. Underneath the compass is a small standard screw slot that an accompanying tool will adjust to whatever your declination is, East or W. In one case the degree is in the eye of the indicator, you're set. None of your azimuths need conversion until such fourth dimension equally you utilise a different compass – one that can't exist adjusted similarly.

If y'all're non using that type of compass, you'll always have both Grid and Magnetic Azimuths to deal with when navigating.

To make up one's mind your GAZ, y'all should utilize one of these, known equally a 'protractor.' Using it is pretty simple: Identify the center over the point on the map yous're using to determine which azimuth you lot're going to travel on, square the protractor to the map'south grid, place a small tick mark in the center of the protractor (they ordinarily have a hole for that purpose), and use some sort of straight edge to line up the heart point and the azimuth (apply the INNER RING of degrees, non the outer band), place a tick mark, move the protractor out of the style, and draw a straight line from the origin point to the azimuth line. You should accept written downwards your Filigree Azimuth (GAZ).

There are others; I prefer the Map Tools 'Super GTA' protractor.

Now on to GAZ to MAZ conversion.

For at present let's say you're using a USGI Lensatic or other compass that does not have the Declination Adjustment feature. The graphic below demonstrates for both East & Due west Declination. You need to know that if your declination is East, it means that Magnetic North is East of your location. Conversely, if it's West, Magnetic North is West of your location.

If y'all plot your grid azimuth on a map and it reads (for instance), 180 degrees (GAZ), and you know your local declination is fifteen degrees E, and y'all wish to catechumen your GAZ to a MAZ, simply subtract the Declination of fifteen degrees and you'll have a 165 MAZ, or 'magnetic' azimuth that you tin utilise with your compass.

Now, if yous want to convert a MAZ to GAZ using the case above (in that yous have a MAZ of 180, simply add the xv degrees declination to the 180, and you accept a right GAZ.

This equationmust be memorized if yous don't accept a declination adjustable compass in order to stay accurate and cease up on or near the coordinate you're aiming for on the concluding leg of your navigation. The consequence of not converting or adjusting for declination is not reaching your objective…..or worse, getting hopelessly lost, which might be terminal, depending on your location and the scenario you find yourself in.

And really, that'south all in that location is to it.

source: https://world wide web.americanpartisan.org/2019/04/essential-skills-converting-filigree-and-magnetic-azimuths-how-and-why/

Author: Michael Hamilton