Ok, but your longitude lines on your map dont follow magnetic north/south, depending on your location. 1790 0 obj <>/Filter/FlateDecode/ID[<2B0C2CAC99B5C942A1B86AECE94C0B5C>]/Index[1778 23]/Info 1777 0 R/Length 68/Prev 337901/Root 1779 0 R/Size 1801/Type/XRef/W[1 2 1]>>stream When using the map and compass method (Figure 6-18). A rule to remember when solving such problems is this: Nomatter where the azimuth line points, the angle to it is always measured clockwise from the reference direction (base line). A protractor is used to measure the angle between grid north and the drawn line, and this measured azimuth is the grid azimuth (Figure 6-4). be Northeast relatively.) If you plot your grid azimuth on a map and it reads (for example), 180 degrees (GAZ), and you know your local declination is 15 degrees East, and you wish to convert your GAZ to a MAZ, simply subtract the Declination of 15 degrees and youll have a 165 MAZ, or magnetic azimuth that you can use with your compass. The magnetic azimuth is determined by using magnetic instruments, such as lensatic and M2 compasses. To convert a grid azimuth to a magnetic azimuth, add the G-M angle. Determine the grid coordinates to the desired accuracy. *!o$8EAbMZIU&G3V`o! Since the location of magnetic north does not correspond exactly with the grid-north lines on the maps, a conversion from magnetic to grid or vice versa is needed. You will find that every zone in a State Plane coordinate system has a central meridian. This sign convention is not necessarily the same for all contractors and should be clearly communicated and understood before drilling begins. GM Angle= 7W 2. YMMV. exceeds the range of the compass, so 403 degrees cannot be the The computation of the grid correction angle or angle of convergence will require special mathematical techniques depending on the type of projection of the curved earth's surface on to the flat grid. The index mark is the center of the protractor circle from which all directions are measured. b. When I was taking a land nav course in the Army I was told this would vary depending on what part of the world you were in. Figure 6-9. endstream endobj 2283 0 obj <>/Metadata 139 0 R/Pages 2280 0 R/StructTreeRoot 171 0 R/Type/Catalog>> endobj 2284 0 obj <>/MediaBox[0 0 612 792]/Parent 2280 0 R/Resources<>/Font<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI]>>/Rotate 0/StructParents 0/Tabs/S/Type/Page>> endobj 2285 0 obj <>stream How do you convert magnetic bearings to grid bearings? (2) Put your finger on the grid north line, now move it to the magnetic north line. If you are surveying or doing something other than land nav for hunting, this may matter. <> On the State Plane coordinate grid, north is always parallel with the central meridian, but at the points on the Earth, north is along the meridian that passes through them. Do not use the diagram to measure a numerical value. The magnitude of the correction angle depends upon its location within the grid and its latitude. Why Walden's rule not applicable to small size cations. Convergence is the difference between geodetic north and grid north. 2 0 obj If it were the other way around (adding the GM angle instead of subtracting in a western state) you would just be INCREASING the difference between your grid and magnetic orientations, rather than making them the same. This is a direct result of the grid north lines being parallel with each other. How to convert magnetic azimuth to grid azimuth. (2) Identify two or three known distant locations on the ground and mark them on the map. For a better experience, please enable JavaScript in your browser before proceeding. Magnetic Azimuth = 90 degrees True Azimuth = Magnetic Azimuth + Declination True Azimuth = 90 + (-15) = 75 degrees Figure 6 Example 2 Grid Convergence Grid convergence is an angle between True North and Grid North. Therefore, (d) Determine the value of the G-M angle. Figure 6-18. (7) The intersection of the lines is your location. (1) Add an easterly G-M angle to a magnetic azimuth to obtain a grid azimuth. 7 0 obj The Pennsylvania State University 2020, GPS and GNSS for Geospatial Professionals, Lesson 6: State Plane Coordinates and Heights, State Plane Coordinate Zones 1983, False Eastings and Scale, Lesson 7: Static Global Positioning System Surveying, Lesson 8: Real-Time Global Positioning System Surveying, Lesson 10: Global Navigation Satellite Systems and the Future, Repository of Open and Affordable Materials, Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, John A. Dutton Institute for Teaching and Learning Excellence, Department of Energy and Mineral Engineering, Department of Materials Science and Engineering, Department of Meteorology and Atmospheric Science, Earth and Environmental Systems Institute, Earth and Mineral SciencesEnergy Institute, iMPS in Renewable Energy and Sustainability Policy Program Office, BA in Energy and Sustainability Policy Program Office, 2217 Earth and Engineering Sciences Building, University Park, Pennsylvania 16802. Add the GM angle to convert a grid azimuth into a magnetic azimuth. Using LARS, convert to a grid azimuth. The site editor may also be contacted with questions or comments about this Open Educational Resource. Converting to a grid azimuth on a map. While this seems a simple task, misunderstandings surrounding the relationship between these references can cause a target to be missed. 5 0 obj WebIn this example, the known azimuth is 270 magnetic. (b) To use a magnetic azimuth in the field with a compass, change the grid azimuth plotted on a map to a magnetic azimuth (Figure 6-14). b. Grid-Magnetic Angle. Draw a magnetic prong from the apex of the grid-north line in the desired direction (Figure 6-9). The G-M angle value is the angular size that exists between grid north and magnetic north. 2287 0 obj <>/Filter/FlateDecode/ID[<01E97BD82B4A724EA381572D5ADBF101><24C8F5536AE732469D3285819F05CE2D>]/Index[2282 15]/Info 2281 0 R/Length 48/Prev 360229/Root 2283 0 R/Size 2297/Type/XRef/W[1 2 1]>>stream Swarovski ATC Compact Spotting Scope Review, Helping Mule Deer Thrive: Muley Fanatic Foundation, Growing Big Mule Deer with Wildlife Prof Randy Larsen. Figure 4. There are 400grads in a circle (a 90-degree right angle equals 100 grads). Doesn't matter if you're in the northern or southern hemisphere. Is Grid North the same as magnetic north? This is the convention for any plane coordinate system, so that north is always up, and always the same direction. An arc indicated by a dashed line connects the prongs for true north and grid north. The name is derived from Old French or Spanish respectively: rumb or rumbo, a line on the chart which intersects all meridians at the same angle. GM Angle= 7W 2. Personally, I prefer maps that use the MGRS (Military Grid Reference System) which is similar to the UTM, but scaled in 1:25,000 & 1:50,000, which is what I learned in during active duty. In the last post onMagnetic Declination, the impact it has on azimuth/bearing accuracy was described. endobj 100 - 80 = 20 Susan is 20 degrees off course. If a mistake is made and the reading is taken from the ending point, the grid azimuth will be opposite, thus causing the user to go in the wrong direction. Theyll either have tick marks on them that you can use to provide your own grid (as I have done and commenters have suggested (Tip: Use very thin map marking pens and dont use red ink red disappears when using a red light) or complete grid lines. GN 4 3 1. 3 0 obj<>>>/MediaBox[0 0 612 792]>> Theyre not essential for shooting an azimuth or bearing (from hear on out referred to as either a Grid Azimuth (GAZ) or Magnetic Azimuth (MAZ)), but they are very, very useful is plotting (determining) positions on a map to within various levels of accuracy (read distance from the actual object being plotted). This is easy to remember. (6) The intersection of the lines on the map is your location. Intersection, using map and compass. Figure 6-19. x]Yo#7~`C?JAXHYd6@Aefl_]~{uOv:e#Y7evu (c) Convert a magnetic azimuth when the G-M angle is greater than the magnetic azimuth (Figure 6-15). This is a direct result of the geodetic north lines converging. 1800 0 obj <>stream WebThe GM angle is used to convert magnetic azimuth to grid azimuth and vice versa: Grid azimuth - determined with a protractor and is measured from grid north. There are two methods of intersection: the map and compass method and the straightedge method (Figures 6-16 and 6-17). You can bypass all the calculations by purchasing a compass that allows you to set your declination. Remember, when taking a reading of a mountain then transfering it to your map, you must do the opposite of what you did when you took a reading from your map. Eight Digit: _____m 7) Convert a grid azimuth of 357 to a magnetic azimuth. It also includes some advanced aspects of map reading, such as intersection, resection, modified resection, and polar plots. How to convert magnetic azimuth to grid azimuth, The how to convert magnetic azimuth to grid azimuth is a question that may be asked in the context of 10 0 obj <>stream The bottom line is this. Determine the grid coordinates to the desired accuracy (Figure 6-17). G-M angle. If you have a magnetic azimuth of 270 degrees, and the G-M angle is 8 degrees, your grid azimuth will be 262 degrees. Conversely, if its West, Magnetic North is West of your location. 4 0 obj <>stream <> Subtract the calculated backsight reading from the original azimuth reading. Magnetic Declination models are updated every year. Hvg dKg|?s::ikP8> Figure 6-12. <>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 612 792] /Contents 10 0 R/Group<>/Tabs/S/StructParents 1>> On the left, at station D266, the convergence is minus 40.0 arcseconds. NORTH IS 0/360 AZIMUTH EAST IS 90. endobj The formula used to convert a geodetic azimuth to a grid azimuth includes the convergence angle, and another element. WebTo convert a magnetic azimuth to a grid azimuth, add the value of the G-M angle to the magnetic azimuth. The G-M angle is important to the map reader/land navigator because azimuths translated between map and ground will be in error by the size of the declination angle if not adjusted for it. (2) Locate at least two known distant locations or prominent features on the ground and mark them on the map. grid azimuth = geodetic azimuth Azimuths are conventionally measured in a clockwise direction from north with 0 degrees corresponding with north, 90 degrees east and 180 degrees south. The graphic below demonstrates for both East & West Declination. Underneath the compass is a small standard screw slot that an accompanying tool will adjust to whatever your declination is, East or West. d. Convert the magnetic azimuth to a grid azimuth. This north base line could be true north, magnetic north, or grid north. The following elements must be present when using polar coordinates (Figure 6-21). (4) Draw a line along the straightedge away from the known position on the ground toward your position. The difference is the 8 angle from True North to Magnetic North plus the 0 23 angle from True North to Grid North. Using a protractor, draw a line for the back azimuth on the map from the known position back toward your unknown position. dy|zn/_|\`dA/xo_vMS@"/9F}6DQ%u>.]l.ny,Vx~#oWCO1[KAVG9m4DyM*7vp`x~\^ ]S,6 (3) Measure the magnetic azimuth to one of the known positions from your location using a compass. When using the protractor, the base line is always oriented parallel to a north-south grid line. Left Add, Right Subtract. For example an azimuth of 140 is greater than 90 and less than 180, therefore it is in SE quadrant. 0 endobj For mils, if the azimuth is less than 3200mils, add 3200 mils, if the azimuth is more than 3200 mils, subtract 3200 mils. Azimuth and A = Azimuth, Disclosure: Some of the links above are affiliate links. 9 0 obj<>>>/MediaBox[0 0 612 792]>> PM Milestone Project Management Templates, Toolface Orientation - Drilling Engineering. Its the little black pincer looking thing. Web(a) To plot a magnetic azimuth on a map, first convert it to a grid azimuth (Figure 6-13). (2) Locate and mark your position on the map. ]od`l`hPh``` " K053NRhU@$4 ;3t0$202EV1/bera`9~H20D(Uf TO So, its good to check the on line or other sources for up to the date declination numbers. compass. Computer programs like GEOMAG use current magnetic models and calculate up-to-date local declination figures. There are three base lines true north, magnetic north, and grid north. (c) Convert a grid azimuth to a magnetic azimuth when the G-M angle is greater than a grid azimuth (Figure 6-12). On the Earth they are not parallel with each other. This circle is divided into 360 degrees or 6400 mils (Appendix G). You see over here on the right at station Fink, the convergence is plus 17.2 arcseconds. Magnetic North. endstream endobj 1785 0 obj <>stream True North. (b) Place the index of the protractor at the point where the drawn line crosses a vertical (north-south) grid line. All lines of longitude are true north lines. (2) Locate and mark your position on the map. Label the borehole azimuth with reference to each system. b. This north base line could be true north, magnetic north, or grid north. Meridians converge on the surface of the Earth. Web1995 G-M ANGLE MILS) 5040 TO CONVERT A MAGNETIC AZIMUTH TOA GRID AZIMUTH ADD G-M ANGLE 0-95 ro GIVE A STANDARD REFERENCE ON THIS SHEET TO NEAREST 100 METERS tifying 100,000 meter point lies: ICAL grid line to LEFT LARGE figures labeling e top or bottom margin.
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