DIRECTIONBeing in the right ar at the prescribed time is essential to successfully accomplish military missions. Direction plays crucial role in a soldier"s day-to-day life. It deserve to be expressed together right, left, directly ahead, and so forth; yet then the inquiry arises, "To the appropriate of what?" This chapter specifies the indigenous azimuth and also the three various norths. It defines in information how to recognize the grid and also the magnetic azimuths v the usage of the protractor and the compass. It describes the use of some field-expedient approaches to find directions, the declination diagram, and the counter of azimuths indigenous grid come magnetic and also vice versa. It additionally includes some progressed aspects that map reading, such as intersection, resection, amendment resection, and polar plots.
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6-1. Approaches OF express DIRECTION
Military personnel require a means of to express direction that is accurate, is adaptable come any part of the world, and also has a typical unit of measure. Directions are expressed as units of angular measure.
a. Degree. The most typical unit of measure is the degree (°) v its subdivisions of minute (") and seconds (").
1 level = 60 minutes.
1 minute = 60 seconds.
b. Mil. an additional unit of measure, the mil (abbreviated ), is used mainly in artillery, tank, and mortar gunnery. The mil expresses the size of an angle formed when a one is split into 6,400 angles, with the peak of the angle at the facility of the circle. A relationship have the right to be established in between degrees and also mils. A circle equals 6400 mils divided by 360 degrees, or 17.78 mils per degree. To convert degrees come mils, multiply degrees by 17.78.
c. Grad. The grad is a metric unit of measure uncovered on some foreign maps. There space 400grads in a one (a 90-degree appropriate angle amounts to 100 grads). The grad is divided into 100centesimal minutes (centigrads) and the minute into 100 centesimal secs (milligrads).
6-2. Basic LINES
In bespeak to measure up something, there must always be a starting point or zero measurement. To express direction as a unit that angular measure, there must be a starting point or zero measure and also a suggest of reference These 2 points point out the base or reference line. There space three base lines—true north, magnetic north, and grid north. The most frequently used room magnetic and also grid.
a. True North. A heat from any suggest on the earth"s surface to the phibìc pole. Every lines of longitude are true phibìc lines. True north is usually represented by a star (Figure 6-1).
Figure 6-1. Three norths.
b. Magnetic North. The direction come the north magnetic pole, as suggested by the north-seeking needle the a magnetic instrument. The magnetic phibìc is normally symbolized by a line finishing with half of one arrowhead (Figure 6-1). Magnetic readings are acquired with magnetic instruments, such as lensatic and M2 compasses.
c. Grid North. The north the is developed by making use of the upright grid present on the map. Net north might be symbolized through the letter GN or the letter "y" (Figure 6-1).
An azimuth is identified as a horizontal angle measured clockwise indigenous a north basic line. This north basic line can be true north, magnetic north, or net north. The azimuth is the most common military technique to refer direction. When using one azimuth, the point from i beg your pardon the azimuth originates is the facility of an imaginary circle (Figure 6-2). This circle is divided into 360 degrees or 6400 mils (Appendix G).
Figure 6-2. Beginning of azimuth circle.
a. Back Azimuth. A back azimuth is the contrary direction of one azimuth. It is equivalent to law "about face." To achieve a earlier azimuth indigenous an azimuth, add 180degrees if the azimuth is 180 levels or less, or subtract 180 degrees if the azimuth is 180degrees or much more (Figure 6-3). The earlier azimuth the 180 levels may be stated as 0degrees or 360 degrees. Because that mils, if the azimuth is less than 3200mils, add 3200 mils, if the azimuth is more than 3200 mils, subtract 3200 mils.
Figure 6-3. Back azimuth.
When converting azimuths into back azimuths, extreme treatment should be exercised when including or subtracting the 180 degrees. A basic mathematical wrong could cause disastrous consequences.
b. Magnetic Azimuth. The magnetic azimuth is identified by using magnetic instruments, such as lensatic and also M2 compasses. Describe Chapter 9, paragraph 4, for details.
c. Field-Expedient Methods. Numerous field-expedient approaches to recognize direction are debated in thing 9, paragraph 5.
6-4. Net AZIMUTHS
When one azimuth is plotted top top a map between point A (starting point) and point B (ending point), the points room joined together by a right line. A protractor is supplied to measure the angle between grid north and the attracted line, and this measure azimuth is the grid azimuth (Figure 6-4).
Figure 6-4. Measure an azimuth.
When measure azimuths top top a map, remember the you space measuring indigenous a starting point come an ending point. If a mistake is made and the reading is taken native the finishing point, the network azimuth will be opposite, therefore causing the user to walk in the wrong direction.
There space several types of protractors—full circle, fifty percent circle, square, and also rectangular (Figure 6-5). All of them division the circle into units the angular measure, and each has actually a scale approximately the outer edge and also an table of contents mark. The index mark is the facility of the protractor circle indigenous which all directions space measured.
Figure 6-5. Varieties of protractors.
Figure 6-6. Army protractor.
b. As soon as using the protractor, the base heat is always oriented parallel to a north-south grid line. The 0- or 360-degree mark is constantly toward the peak or phibìc on the map and the 90° note is come the right.
(1) To determine the grid azimuth—
(a) attract a line connecting the two points (A and also B).
(b) ar the index of the protractor at the allude where the drawn line crosses a upright (north-south) net line.
(c) keeping the table of contents at this point, align the 0- come 180-degree heat of the protractor on the vertical grid line.
(d) read the value of the angle from the scale; this is the grid azimuth from point A to point B (Figure 6-4).
(2) come plot one azimuth native a known point on a map (Figure 6-7)—
(a) transform the azimuth indigenous magnetic to grid, if necessary. (See i 6-6.)
(b) ar the protractor top top the map v the index mark at the facility of mass of the known suggest and the base heat parallel come a north-south grid line.
(c) do a note on the map at the wanted azimuth.
(d) eliminate the protractor and draw a line connecting the known suggest and the mark on the map. This is the grid direction heat (azimuth).
|NOTE:||When measuring an azimuth, the analysis is always to the nearest level or 10mils. Street does not change an accurately measure up azimuth.|
Figure 6-7. Plotting an azimuth ~ above the map.
c. To obtain specific reading with the protractor (to the nearest level or 10 mils), there are two techniques to examine that the base heat of the protractor is parallel to a north-south grid line.
(1) location the protractor index whereby the azimuth line cut a north-south network line, aligning the base heat of the protractor straight over the intersection of the azimuth line with the north-south network line. The user should be able to determine even if it is the initial azimuth analysis was correct.
(2) The user need to re-read the azimuth between the azimuth and north-south grid heat to inspect the early azimuth.
(3) keep in mind that the protractor is reduced at both the top and also bottom by the same north-south network line. Count the number of degrees from the 0-degree note at the optimal of the protractor to this north-south network line and then count the variety of degrees native the 180-degree mark at the bottom that the protractor to this same grid line. If the 2 counts are equal, the protractor is appropriately aligned.
6-6. DECLINATION DIAGRAM
Declination is the angular distinction between any kind of two norths. If you have a map and a compass, the one of most interest to you will be between magnetic and grid north. The declination diagram (Figure 6-8) reflects the angular relationship, stood for by prongs, among grid, magnetic, and true norths. When the family member positions of the prongs room correct, they are seldom plotted to scale. Perform not usage the diagram to measure a numerical value. This value will be written in the map margin (in both degrees and mils) alongside the diagram.
Figure 6-8. Declination diagrams.
a. Location. A declination chart is a component of the info in the lower margin ~ above most larger maps. On medium-scale maps, the declination details is displayed by a note in the map margin.
b. Grid-Magnetic Angle. The G-M angle value is the angular size that exists between grid north and magnetic north. That is one arc, indicated by a dashed line, the connects the grid-north and also magnetic-north prongs. This worth is expressed come the nearest 1/2 degree, v mil equivalents shown to the nearest 10 mils. The G-M angle is vital 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 readjusted for it.
c. Grid Convergence. An arc indicated by a dashed line connects the prongs for true north and also grid north. The value of the angle because that the facility of the sheet is provided to the nearest full minute through its tantamount to the nearest mil. This data are presented in the form of a grid-convergence note.
d. Conversion. there is an angular difference in between the net north and the magnetic north. Because the place of magnetic phibìc does no correspond exactly with the grid-north present on the maps, a conversion indigenous magnetic to grid or vice versa is needed.
(1) With Notes. Merely refer to the conversion note that appear in conjunction through the diagram explaining the usage of the G-M angle (Figure 6-8). One note offers instructions because that converting magnetic azimuth come grid azimuth; the other, because that converting net azimuth come magnetic azimuth. The switch (add or subtract) is governed by the direction the the magnetic-north prong relative to the of the north-grid prong.
(2) Without Notes. In some cases, there room no declination conversion notes on the margin the the map; that is important to transform from one kind of declination come another. A magnetic compass offers a magnetic azimuth; but in order come plot this line on a gridded map, the magnetic azimuth value need to be changed to grid azimuth. The declination diagram is provided for these conversions. A rule to remember when solving such troubles is this: Nomatter wherein the azimuth heat points, the angle to that is constantly measured clockwise from the referral direction (base line). With this in mind, the difficulty is fixed by the complying with steps:
(a) attract a vertical or grid-north heat (prong). Constantly align this line through the vertical lines top top a map (Figure 6-9).
Figure 6-9. Declination diagram through arbitrary line.
(b) from the basic of the grid-north line (prong), draw an arbitrary line (or any type of azimuth line) at a roughly right angle to north, nevertheless of the actual value of the azimuth in levels (Figure 6-9).
(c) research the declination chart on the map and determine the direction the the magnetic north (right-left or east-west) family member to the of the grid-north prong. Attract a magnetic prong native the apex the the grid-north heat in the preferred direction (Figure 6-9).
(d) identify the value of the G-M angle. Draw an arc indigenous the network prong to the magnetic prong and place the value of the G-M angle (Figure 6-9).
(e) complete the chart by illustration an arc from each reference line come the arbitrary line. A glance at the perfect diagram mirrors whether the provided azimuth or the preferred azimuth is greater, and also thus whether the recognized difference in between the two have to be included or subtracted.
(f) The consist of of the true-north prong in relationship to the conversion is of small importance.
e. Applications. Remember, there space no negative azimuths on the azimuth circle. Because 0 level is the exact same as 360 degrees, climate 2 levels is the very same as 362 degrees. This is because 2 degrees and 362 levels are located at the same suggest on the azimuth circle. The network azimuth deserve to now it is in converted into a magnetic azimuth because the network azimuth is now bigger than the G-M angle.
(1) when working through a map having actually an eastern G-M angle:
(a) to plot a magnetic azimuth ~ above a map, first change it come a net azimuth (Figure 6-10).
Figure 6-10. Converting to net azimuth.
(b) To use a magnetic azimuth in the ar with a compass, very first change the net azimuth plotted top top a map come a magnetic azimuth (Figure 6-11).
Figure 6-11. Convert to magnetic azimuth.
(c) convert a network azimuth to a magnetic azimuth once the G-M edge is greater than a network azimuth (Figure 6-12).
Figure 6-12. Converting to a magnetic azimuth once the G-M angle is greater.
(2) as soon as working v a map having a west G-M angle:
(a) to plot a magnetic azimuth top top a map, first convert it to a net azimuth (Figure 6-13).
Figure 6-13. Converting to a grid azimuth on a map.
(b) To usage a magnetic azimuth in the field with a compass, adjust the network azimuth plotted on a map come a magnetic azimuth (Figure 6-14).
Figure 6-14. Convert to a magnetic azimuth top top a map.
(c) convert a magnetic azimuth once the G-M angle is greater than the magnetic azimuth (Figure 6-15).
Figure 6-15. Converting to a net azimuth as soon as the G-M angle is greater.
(3) The G-M angle diagram should be constructed and used each time the switch of azimuth is required. Such procedure is important when working through a map because that the first time. It likewise may be convenient to construct a G-M angle conversion table ~ above the margin the the map.
|NOTE:||When convert azimuths, exercise extreme care when including and subtracting the G-M angle. A an easy mistake of 1° might be far-reaching in the field.|
Intersection is the ar of an unknown point by successively occupying at least two (preferably three) known positions on the ground and also then map sighting on the unknown location. The is provided to locate remote or inaccessible clues or objects together as adversary targets and danger areas. There room two approaches of intersection: the map and also compass method and the straightedge an approach (Figures 6-16 and 6-17).
Figure 6-16. Intersection, utilizing map and also compass.
Figure 6-17. Intersection, making use of a straightedge.
a. As soon as using the map and compass method—
(1) Orient the map making use of the compass.
(2) Locate and also mark your position on the map,
(3) identify the magnetic azimuth to the unknown place using the compass.
(4) convert the magnetic azimuth come grid azimuth.
(5) attract a heat on the map indigenous your place on this grid azimuth.
(6) move to a second known suggest and repeat measures 1, 2, 3, 4, and also 5.
(7) The ar of the unknown place is where the lines cross on the map. Recognize the grid coordinates to the wanted accuracy.
b. The right edge technique is provided when a compass is no available. When using it—
(1) Orient the map ~ above a level surface by the terrain combination method.
(2) Locate and also mark your place on the map.
(3) place a straight edge on the map v one end at the user"s place (A) as a pivot point; then, revolve the straightedge until the unkown point is sighted follow me the edge.
(4) draw a line along the directly edge
(5) Repeat the over steps at position (B) and also check because that accuracy.
(6) The intersection that the currently on the map is the ar of the unknown suggest (C). Recognize the grid collaborates to the wanted accuracy (Figure 6-17).
Resection is the method of locating one"s place on a map by identify the net azimuth to at the very least two well-defined locations that can be pinpointed top top the map. For higher accuracy, the desired an approach of resection would be come use three or much more well-defined locations.
a. Once using the map and also compass technique (Figure 6-18)—
(1) Orient the map making use of the compass.
(2) identify two or three known far-off locations top top the ground and mark lock on the map.
(3) measure the magnetic azimuth to among the recognized positions from your location using a compass.
(4) convert the magnetic azimuth come a net azimuth.
(5) transform the net azimuth to a back azimuth. Using a protractor, draw a line for the back azimuth on the map indigenous the recognized position ago toward your unknown position.
(6) Repeat 3, 4, and 5 for a second position and a 3rd position, if desired.
(7) The intersection of the lines is your location. Determine the grid coordinates to the wanted accuracy.
Figure 6-18. Resection through map and also compass.
a. When using the straightedge an approach (Figure 6-19)—
(1) Orient the map ~ above a flat surface by the terrain association method.
(2) locate at the very least two known remote locations or prominent attributes on the ground and mark lock on the map.
(3) put a straightedge on the map utilizing a known position together a pivot point. Revolve the straightedge till the recognized position on the map is aligned through the known position on the ground.
(4) attract a line follow me the straightedge away from the well-known position top top the ground toward your position.
(5) Repeat 3 and 4 using a second known position.
(6) The intersection that the currently on the map is her location. Identify the grid collaborates to the wanted accuracy.
Figure 6-19. Resection through straightedge.
6-9. Modification RESECTION
Modified resection is the method of locating one"s position on the map when the human being is situated on a linear function on the ground, such together a road, canal, or present (Figure 6-20). Continue as follows:
a. Orient the map using a compass or by terrain association.
b. Uncover a distant allude that have the right to be established on the ground and on the map.
c. Identify the magnetic azimuth native your place to the far-off known point.
d. Convert the magnetic azimuth to a network azimuth.
e. Transform the net azimuth to a ago azimuth. Using a protractor, attract a line because that the earlier azimuth top top the map native the known position earlier toward your unknown position.
f. The ar of the user is where the line the cross the linear feature. Determine the grid collaborates to the preferred accuracy.
Figure 6-20. Modification resection.
6-10. POLAR COORDINATES
A method of locating or plot an unknown position from a known point by providing a direction and also a distance along that direction heat is referred to as polar coordinates. The following elements must be present when making use of polar works with (Figure 6-21).
Present known location on the map.
Azimuth (grid or magnetic).
Distance (in meters).
Figure 6-21. Polar plot.
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Using the laser range finder to determine the variety enhances your accuracy in identify the unknown position"s location.