Plot 8 Digit Grid
MGRS vs UTM
- How To Plot 8 Digit Grid Coordinates
- Plot A 8 Digit Grid
- Plot 8 Digit Grid Military Map
- How To Plot 8 Digit Grid
- 8 Digit Grid Coordinate
Determine Six-Digit Grid Coordinate 1. Place your protractor scale on the Zero-Mark(+) 6 3 The 6 digit grid coordinate is 786 003 2. Slide the protractor scale along the horizontal axis) 3. Stop as the vertical axis intersects the plot point 4. Read RIGHT along the horizontal axis 5. Round to the nearest whole number: 6 6. You will receive four 8-digit grid coordinates which you must plot, correctly, on your map. Once this is done, you can start your navigation. The only items you will carry are: pencil, protractor, map, score sheet, and compass. You have 3 hours to complete the course and find 3 of 4 points. How to calculate you 8-digit grid square Les Peters, N1SV (FN42ep09) The Maidenhead Locator System is a method for identifying positions on the Earth and commonly used by VHF / UHF enthusiasts. A maidenhead locator represents a position on the Earth based on latitude and longitude. This position information is represented in.
MGRS uses a system of numbers and letters to display UTM coordinates.
The Maryland state house is at N38°58.739' W76°29.456' in Annapolis. Coordinates always read 'Right, Up', with x first and then y. This contrasts with lat/long, which generally have latitude (y) first.
UTM--Universal Transverse Mercator | |||
| UTM Zone | Hemisphere | false easting (m) | northing (m) |
| 1-60 | N,S | 100,000-900,000 | 0--10,000,000 |
| 18 | N | 370823 | 4315291 |
UTM coordinates may be given as 18N 370823E 370823N, but there is no absolute standard. Easting is generally given first.
UTM has a false easting of 500,000 at the central meridian of each UTM zone, and a false northing in the southern hemisphere. These allow UTM coordinates to avoid negative numbers.
MGRS--Military Grid Reference System | |||||
| UTM Zone | Lat Band | 100K grid square | easting | northing | Accuracy |
| 1-60 | C-X (No I, O) | ||||
| 18 | S | UJ | 70823 | 15291 | 1 meter |
| 18 | S | UJ | 7082 | 1529 | 10 meters |
| 18 | S | UJ | 708 | 152 | 100 meters |
| 18 | S | UJ | 71 | 15 | 1000 meter |
| 18 | S | UJ | 7 | 1 | 10 km |
MGRS is given as one continuous string, and the user knows how to break it up. This example would be 18SUJ7082315291, or 18SUJ70821529, or 18SUJ708152. The easting and northing are always given to the same level of accuracy, so that the last portion of a MGRS coordinate always has an even number of digits after the two letters of the 100K grid square.
The 100K grid squares use the letters C to X; they omit the letters I and O to avoid confusion with the numbers 1 and 0. Letters A and B are used for the South Pole and Y-Z are used for the North Pole in the polar stereographic projection.
Note that MGRS eastings and northings omit one digit on the easting (3 in this case), and generally two on the northing (43 in this case; it would be one digit very close to the equator in the northern hemisphere), which are included with the 100K grid letters.
When dealing with a small area when all concerned know the region, you can omit the UTM Zone and Lat Band, and for even smaller areas you can also omit the 100K grid square. In that case you could transmit 6, 8, or 10 digit coordinates depending on the accuracy required.
| On military maps, the grid typically shows two coordinates in both the x and y directions. They are indicated in the margins, and often within the main part of map centered on some grid lines. |
The US National Grid (USNG) is actually MGRS.
UTM grid on maps.
Last revision 9/16/2015
Chapter 6
FIRING CHARTS
One of the elements to the solution of the gunnery problem is the determination of chart data. Chart data consist of chart range, chart deflection, and angle T. The determination of chart data requires the construction and operation of firing chart.
Section I
Types of Firing Charts
| This section implements a portion of QSTAG 224. |
Two types of firing charts may be constructed in the FDC. They are surveyed firing charts and observed firing charts. Regardless of the type constructed two firing charts are maintained in a manual FDC. The horizontal control operator (HCO) maintains the primary firing chart, and the vertical control operator (VCO) maintains a backup, or check, chart and a 1:50,000-scale situation map with tactical overlay(s).
6-1. Description
A firing chart is a graphic representation of a portion of the earth's surface used for determining distance (or range) and direction (azimuth or deflection). The chart may be constructed by using a map, a photomap, a grid sheet, or other material on which the relative locations of batteries, known points, targets, and observers can be plotted. Additional positions, fire support coordinating measures, and other data needed for the safe and accurate conduct of fire may also be recorded.
6-2. Firing Chart Construction
The most commonly used materials for constructing firing charts are as follows:
a. Grid Sheet. A grid sheet is a plain sheet of paper or plastic (mylar) on which equally spaced horizontal and vertical lines, called grid lines, are printed. The intervals between these grid lines will create 1,000-meter grid squares on a scale of 1:25,000. This scale provides the best compromise between accuracy and convenience and is therefore the scale for which standard plotting equipment is graduated. The locations of all points plotted on the grid sheet must be determined either by survey data, map inspection, or firing. The grid sheet is numbered to correspond to the map area of the zone of operation of the supported force. The FDO assigns the lower left-hand corner casting and northing coordinates, and the direction of the long axis (east-west or north-south) also is specified. The rightmost and topmost grid lines are not labeled because data are not determined from these grid lines.
b. Map. A map is a graphic representation, drawn to scale, of a portion of the earth's surface. Only maps based on accurate ground survey should be used for constructing firing charts. If the map scale is other than 1:25,000, the range readings obtained from plotting equipment must be adjusted. For example, if a 1:50,000-scale map is used, the ranges determined with the RDP must be doubled. Deflections and azimuths are not affected. If a map is not based on accurate and adequate ground survey control, it should be used only to obtain approximate locations and vertical control to supplement a grid sheet firing chart.
c. Photomap. A photomap is a reproduction of an aerial photograph or a mosaic of aerial photographs on which grid lines, marginal information, and place names are superimposed. A photomap must not be considered exact until its accuracy has been verified. Photomaps may include errors caused by tilt, distortion caused by relief, and errors caused by poor assembly, If points cannot be located on the photomap by inspection, the photomap scale must be determined before points can be located on the photomap survey. Normally, vertical control can be established by estimation only. Determination of the scale of vertical control of photographs is discussed in FM 21-26. Some photomaps have spot altitudes, but interpolation for altitude is difficult and inaccurate.
Section II
Plotting Equipment and Firing Chart Preparation
To ensure the accuracy of the data shown on the firing chart, FDC personnel should construct and plot from a standing position directly above the chart. Plotting pins must be kept perpendicular to the firing chart. Personnel, equipment and the firing chart should be kept as clean as possible at all times. If two charts are present in the FDC, they must be checked against each other for accuracy. If one chart is a backup for another system, it should be verified against that system for accuracy. (Refer to Appendix E for automated FDC procedures.)
6-3. Pencils
a. 6H Pencil. The 6H (hard lead) pencil is sharpened to a wedge point and is used to draw fine index lines from which measurements are made. If a 6H pencil is not available, a 5H pencil is an acceptable substitute. (See Figure 6-1.) Place a 1-inch piece of tape on the end to differentiate between a 4H pencil.
b. 4H Pencil. The 4H pencil is sharpened to a conical point and is used to label and construct tick marks and to label azimuth and deflection indexes. If a 4H pencil is not available, a 3H pencil is an acceptable substitute. (See Figure 6-2.)
c. Red and Blue Pencil. The red and blue pencil is sharpened to a conical point and is used to label and construct tick marks and label deflection indexes, as required by the color code. (See Figure 6-2.)
d. Orange Pencil. The orange pencil is sharpened to a conical point and is used to label tick marks and deflection indexes, as required by the color code. (See Figure 6-2.)
e. Green Pencil. The green pencil is sharpened to a conical point and is used to label tick marks for radars, as required by the color code. (See Figure 6-2.)
6-4. Plotting Pins
Plotting pins are used to mark indexes and temporary positions on the firing chart. On a 1:25,000-scale chart, the thickness of the plotting pin shaft equals 20 meters.
6-5. Plotting Scale
The plotting scale is a square-shaped scale used to plot or determine grid coordinates. The scale is graduated in meters and yards at scales of 1:25,000 and 1:50,000. Using the four-step plotting method, locations are normally plotted to an accuracy of 10 meters with the plotting scale. Personnel must be careful not to confuse the meter and yard scales on this instrument (newer plotting scales only have meter scales on them). (See Figure 6-3.) If there is a yard scale, tape over it so this scale is not accidentally used.
| NOTE: Ten-digit grid coordinates are expressed to an 8-digit grid coordinate when plotting because of the limitations of the plotting scale. |
6-6. Range-Deflection Protractor
The RDP is used to measure angles in mils and distances in meters. Range and deflection are measured from a firing unit to a target. Direction and distance are measured from an observer to a target. (See Figure 6-4.)
a. The left edge of the instrument is the arm and is used to measure range or distance. It is graduated in 50-meter increments and labeled every 500 meters on a scale of 1:25,000. Ranges and distances are visually interpolated to an accuracy of 10 meters. The arm can be labeled to represent charge or range spans and other pertinent data to aid the FDO.
b. The 1,000-mil arc of the RDP is graduated in 5-mil increments. The 50-mil increments are indicated by longer graduations and are permanently numbered. The are is visually interpolated to an accuracy of 1 mil.
c. The vertex, the slotted portion of the RDP, is placed against a plotting pinto properly position the RDP for determining data.
d. There are four different RDP models. They differ by the maximum range of the arm (12,000, 15,000,25,000, and 30,000 meters).
e. RDPs are also available on a 1:50,000 scale.
| NOTE: When labeling the RDP, label azimuth values in blue and deflection values in red. |
6-7. Target Grid
The target grid is a circular paper device on which grid lines are printed. Normally, the target grid used is DA Form 4176 (Target Plotting Grid, Field Artillery). Grid lines on the target grid match the scale of the 1:25,000 firing chart, dividing a 1,000-meter grid square into 100-meter squares. An azimuth scale is printed around the outer edge of the target grid. It is graduated in 10-mil increments and is numbered every 100 mils. An arrow extends across the center of the target grid and is used to indicate the observer-target line (or other line of known direction). The target grid should be labeled as shown in Figure 6-5. (The L and - are written in blue pencil; the R and +, in red.) Transparent tape should be applied to the reverse side of the target grid to prevent the center hole from becoming enlarged. The target grid is used for three distinct operations:
- Plotting the position of targets located by a shift from a known point.
- Plotting observer subsequent corrections.
- Determing angle T.
Section III
Surveyed Firing Chart
A surveyed firing chart is a chart on which the location of all required points (battery or platoon positions, known points, and OPs) are plotted. These locations can be based on survey or map inspection. All plotted points are in correct relations to one another and reflect actual map coordinates.
6-8. Selection of Lower Left-Hand Corner and Azimuth of Lay
For the chart operator to construct a firing chart correctly, he needs to be provided guidance on what coordinates to assign to the lower left-hand comer (LLHC) of the grid sheet and the azimuth of lay. The FDO is responsible for providing this information. The azimuth of lay can be determined on the basis of the zone of operations or the guidance from the battery commander or higher HQ. After the azimuth of lay is determined, the LLHC coordinates need to be carefully selected. The selected LLHC coordinates should include all critical points on the firing chart and allow full use of the RDP. The steps in Table 6-1 will help to serve as a guide in determining the LLHC and azimuth of lay.
6-9. Firing Chart Preparation
The steps in Table 6-2 are the recommended sequence for the preparation of a firing chart.
6-10. Four-Step Plotting Method
Points commonly plotted on a firing chart include battery or platoon base piece locations, known points, targets, observer locations, and maneuver checkpoints. Base piece locations can be determined by using the M17 plotting board and protractor. To plot points located by grid coordinates, use the steps in Table 6-3.
6-11. Tick Marks
The tick mark is the symbol used to mark and identify the location of a point plotted on a firing chart. The tick mark is constructed in the form of a cross with each arm beginning 40 meters from the pinhole on the chart and extending 160 meters in length (1:25,000 scale).
| NOTE: Tick marks will be constructed with a 4H pencil with the following exception: To construct a tick mark for a target that has been located through firing, use a red pencil. |
Table 6-4 uses the 3,5,7, method to construct a tick mark.
6-12. Construction of Azimuth Indexes
Azimuth indexes are constructed for points located on the firing chart from which the polar method of target location may be expected. The RDP is prepared by numbering the 100-mil azimuth graduations in blue as shown in Figure 6-4. Azimuths are always read as four digits. The first digit (thousands of mils) is read from an index that is constructed on the firing chart. The last three digits are read from the arc of the RDP. Azimuth indexes are constructed on the firing chart in 1,000-mil intervals throughout the target area, except the 6000 and 0 indexes, which are 400 mils apart. The steps for constructing azimuth indexes can be found in Table 6-5.
NOTE: To help determine the four digits of a deflection or azimuth, use the memory aid CLUE. C - Chart index/ pin is first digit. L - Label on RDP arc is second digit. U - Unit graduation is third digit. E - Estimate (visually) to nearest mil is fourth digit. |
6-13. Construction of Deflection Indexes
Direction from a battery or platoon to a target normally is measured and announced in terms of deflection. Deflection is the horizontal clockwise angle from the line of fire, or the rearward extension of the line of fire, to the line of a designated aiming point with the vertex of the angle at the sight. In addition to the deflection as a fire command, the firing battery is concerned with common deflection. The RDP will be used to measure deflection so it must be prepared by numbering the graduations of the arc in red as shown in Figure 6-4. Orient the RDP on the azimuth of fire, and place a pin opposite the common deflection for that weapon system. Table 6-6 contains the steps required for constructing deflection indexes.
6-14. Plotting Targets
The observer can use three methods of target location: grid coordinate, polar plot, and shift from a known point. The steps for plotting targets on a firing chart are listed in Table 6-7.
6-15. Determining and Announcing Chart Data
Chart data consist of chart range and chart deflection from the firing unit to the target and angle T. In a manual FDC, two firing charts will be constructed and will be used to check each other. Use the steps in Table 6-8 to determine chart data.
6-16. Chart-to-Chart Checks
a. One chart may differ slightly from another because of small differences in construction caused by human limitations in reading the graphical equipment. Because of these differences, the following tolerances between charts are permissible:
- Range and/or distance ±30 meters.
- Azimuth and/or deflection ±3 mils.
- Angle T ±30 mils.
b. All firing unit locations must be checked for accuracy. For checking the accuracy of two or more charts, plot the same grid intersection on all charts. Determine range and deflection to that grid intersection. If all ranges agree within ±30 meters in range and ±3 mils in deflection, the charts are accurate for that firing unit location. If not, all charts must be checked for errors.
c. To ensure accuracy, enough points in the zone of operation of a firing unit should be checked. For example, an error in plotting the unit location on one chart could compensate for an error in constructing the deflection index on the other chart. Checking at least two points will reveal the error. This should be done as a matter of unit SOP.
Section IV
Observed Firing Charts
When survey control and maps are not available, delivery of indirect fires is possible by using observed firing charts. An observed firing (OF) chart is a firing chart on which all units and targets are plotted relative to each other from data determined by firing a registration. Observed firing charts are an expedient method that should only be use under emergency conditions and every attempt should be made to construct a surveyed firing chart as soon as possible. Since all locations are based upon firing data, observed firing charts contain errors because of nonstandard conditions.
6-17. Overview
a. All observed firing charts are based on a registration. Once a registration is complete, the unit location is polar plotted from the point of registration (normally assumed to be a grid intersection) by using the direction that is based on the back azimuth to the point and a range corresponding to the adjusted elevation, or more preferably, a range corresponding to the adjusted time.
b. Because maps and survey are not available, altitudes cannot be accurately determined. When vertical interval and site are assumed to be zero, a false range is introduced into the polar plot range. This inaccuracy can be reduced by trying to determine site. Site may be determined by estimating vertical interval or by conducting an XO's high burst.
c. The general procedures for constructing an OF chart are listed below:
(1) Mark the center of sector for observers.
(2) The observer selects a point in the center of the sector of fire that can be identified on the ground.
(3) Assign the point an arbitrary grid coordinate and altitude. Plot this location on the firing chart. The grid coordinates assigned to the point are completely arbitrary. A grid intersection is preferred for simplicity. The grid coordinates of the known point will serve as the basis for establishing a common grid system. For example, the point could be assigned the grid coordinates of easting (E): 20000 northing (N): 40000, altitude 400 meters. (See Figure 6-23.)
(4) Conduct a precision registration (fuze time, if possible) on the point by using emergency firing chart procedures. (See Chapter 14.)
(5) Determine the adjusted data (to include orienting angle, if possible).
(6) From the adjusted data, determine direction (azimuth) and distance (range) from the point to the unit.
(7) Polar plot the base piece from the point.
6-18. Methods of Determining Polar Plot Data
a. All observed firing charts are constructed by using polar plot data. The method for obtaining these data depends on the type of registration conducted and whether site can be estimated or whether it is unknown.
b. Percussion plot is used when an impact registration has been conducted.
(1) When VI is not known and cannot be estimated, the method is known as percussion plot, VI unknown.
(2) When vertical interval can be estimated, a site can be determined and inaccuracies reduced. This method is known as percussion plot, VI estimated.
c. Time plot is used when a time registration has been conducted.
(1) When VI is not known, the method is known as time plot, VI unknown.
(2) When VI can be determined by using an XO's high-burst registration, the method is known as time plot, VI known.
6-19. Constructing Observed Firing Charts
The step-by-step procedures for construction of an observed firing chart are listed in Table 6-9.
6-20. Determination of Direction for Polar Plotting
a. Once the registration has been completed, the azimuth of the line of fire must be determined. No matter what technique (percussion or time plot) is used, the direction (azimuth) of the firing unit from the known point is computed in the same manner.
b. There are two methods to determine the azimuth of the line of fire. They are as follows:
(1) The XO or platoon leader will determine the azimuth of the line of fire in accordance with FM 6-50 and report it to the FDC.
(2) The drift corresponding to the adjusted elevation is stripped out of the adjusted deflection; the result is the chart deflection. The chart deflection is then converted to an azimuth. For example in Figure 6-24, the firing unit was laid on grid azimuth 6100; common deflection 3200. The adjusted deflection was 3346, and the adjusted elevation was 272.
ADJUSTED DEFLECTION 3346
-DRIFT ~ ADJUSTED ELEVATION-L5
CHART DEFLECTION 3341
CHART DEFLECTION 3341
COMMON DEFLECTION -3200
DIFFERENCE IN DEFLECTIONS L141
(USE LARS RULE FOR DEFLECTION)
GRID AZIMUTH 6100
+DIFFERENCE IN DEFLECTIONS+L141
(USE RALS RULE FOR AZIMUTH)
AZIMUTH FOR THE LINE OF FIRE 5959
c. Because the firing unit will be polar plotted from the known point, the FDC must convert the azimuth of the line fire to a back azimuth. The polar plot direction is simply the back azimuth of fire to the known point. The polar plot direction equals the azimuth of the line of fire ±3,200 mils. If the adjusted (adj) azimuth of fire is less than 3,200 mils, add 3,200 mils to it. If the adjusted azimuth of fire is greater than 3,200 mils, subtract 3,200 mils from it.
AZIMUTH OF THE LINE OF FIRE 5959
±3200 MILS -3200
POLAR PLOT DIRECTION 2759
| NOTE: When the azimuth of the line of fire is measured, the howitzer is aimed with the adjusted deflection. This will result in a polar plot azimuth that compensates for drift. If the drift corresponding to the adjusted elevation is removed and a chart deflection is determined all nonstandard conditions (other than drift) affecting the deflection are accounted for in the plot of the known point. |
d. Once the polar plot direction has been computed, the remaining polar plot data must be computed by using one of the methods listed below.
(1) If the impact registration was conducted and VI is not known and cannot be estimated, use the percussion plot, VI unknown method, as shown in paragraph 6-21.
(2) If the impact registration was conducted and VI can be estimated, use the percussion plot, VI estimated method, as shown in paragraph 6-22.
(3) If time registration was conducted and VI is unknown, use the time plot, VI unknown method, as shown in paragraph 6-23.
(4) If time registration was conducted and VI is to be determined by using the XO's high burst, use the time plot, VI known method, as shown in paragraph 6-24.
6-21. Percussion Plot, VI Unknown
Percussion plot is used when an impact registration has been conducted. When VI is not known and cannot be estimated, the method is known as percussion plot, VI unknown. The percussion plot technique assumes that site is zero. The range used to polar plot is the range corresponding to the adjusted elevation. Since site is zero, the adjusted quadrant elevation is the same as the adjusted elevation.
UNIT ALTITUDE = KNOWN POINT ALTITUDE
POLAR PLOT RANGE = RANGE CORRESPONDING TO ADJUSTED ELEVATION
6-22. Percussion Plot, VI Estimated
When site is assumed to be zero, a large error can be introduced into the computation of range by using the percussion plot technique. This error can be minimized and the accuracy of the chart improved by estimating a vertical interval between the firing unit and the known point. The firing unit altitude is then determined by applying the estimated VI from the assumed altitude of the known point to the firing unit altitude. (See Figure 6-25.) The estimated VI is used to compute site as shown in Table 6-10.
6-23. Time Plot, VI Unknown
a. The lack of an accurate site and nonstandard conditions are the major sources of error in range on an observed firing chart. If the site is unknown or incorrect, the derived adjusted elevation is in error by the amount of error in site. Determining the polar plot range from the false elevation produces a false range. However, the effect of site on fuze settings is usually small. Therefore, the adjusted time can be used as a good indicator of the adjusted elevation and the polar plot range. Because the adjusted fuze setting is a function of elevation and complementary angle of site (CAS), the angle of site (SI) and hence the VI may be determined after the firing of fuze time.
b. To derive angle of site, subtract the elevation corresponding to the adjusted time plus the CAS from the adjusted quadrant elevation. Using the GST, determine the VI by multiplying the polar plot range by the derived angle of site. To determine range, place the MHL of the GFT over the adjusted time and read range under the MHL from the range scale. Determine altitude of the firing unit by applying the VI to the assumed altitude of the known point.
ADJ QE = (ADJUSTED ELEVATION + CAS) + SI.
6-24. Time Plot, VI Known (Preferred Technique)
a. When site can be determined by using an XO's high-burst (HB) registration, the method is known as time plot, VI known. This provides an even more accurate relative location.
(1) This technique is based on a rough approximation of site. This approximation can be refined to an accuracy approaching survey accuracy by the firing of a modified HB registration after the completion of a precision registration with fuze time.
(2) The objective of an XO's HB registration is to determine precisely what portion of the adjusted QE is angle of site and what portion is elevation plus CAS. (See Figure 6-26.) The vertical interval and site to the known point can be computed by using the angle of site and range corresponding to the adjusted time.
ADJ QE = (ADJ EL + CAS) + SI.
(3) This XO's HB registration is based on the principle that fuze setting is a fiction of elevation plus CAS. The XO's HB registration is fired immediately after the time portion of the registration is completed. The firing of three such high airbursts is specifically what is called XO's HB registration. The height of burst is raised vertically by an amount sufficient to enable the burst to be seen by an aiming circle located within 30 meters of the registering piece. The burst is raised by increasing quadrant. Three rounds are fired with the adjusted time. The XO measures the angle of site to each burst and determines the average angle of site. Because the fuze setting was not changed (the adjusted time was freed), the elevation plus CAS determined is the true elevation plus CAS. This value is then subtracted from the adjusted QE, yielding a true angle of site. Site is then computed.
b. The procedures for conducting an XO's HB registration are outlined in Table 6-11.
c. After understanding the theory on which the determination of site by firing is based, it may be easier to use the GOT MINUS ASKED FOR rule to determine the angle of site. As shown in Figure 6-27, the angle of site to the known point equals got minus(-) asked for. The procedures for the GOT MINUS ASKED FOR rule are in Table 6-12.
6-25. Setting Up the Observed Firing Chart
At the completion of any of the four techniques demonstrated, the HCO will construct an observed firing chart by using the steps in Table 6-13.
6-26. Example of Percussion Plot, VI Unknown.
A registration was conducted with shell HE, charge 4GB. The site and firing unit altitude are unknown.
a. The following data are known:
Adjusted quadrant elevation: 272
Azimuth of the line of fire reported
by the XO or platoon leader: 5959
Adjusted deflection: 3346
Assumed altitude of the known point: 400
b. Determine the direction, altitude, and range from the known point to the firing unit.
(1) Determine the polar plot direction. The azimuth of the line of fire ±3200 equals polar plot direction.
(2) Determine the firing unit altitude. The firing unit altitude equals the known point altitude.
(3) Determine the polar plot range. The polar plot range equals the range that corresponds to the adjusted QE.
6-27. Example of Percussion Plot, VI Estimated
The observer passes the firing unit position on his way to his location and estimates the VI to be +60 meters. Use the known data from paragraph 6-26.
a. Determine the first apparent site. RG ~ ADJ QE = 4560 METERS. Using the GST, set +60 underneath the MHL on the D scale. Move the site-range scale for charge 4GB TAG until range 4560 is underneath the MHL. Read site underneath the M gauge point on the D scale.
FIRST APPARENT SITE = +14 MILS
b. Determine the first apparent elevation.
ADJUSTED QE 272
- FIRST APPARENT SITE+14
FIRST APPARENT ELEVATION 258
RG ~ FIRST APPARENT EL = 4,370 METERS
c. Determine the second apparent site. RG ~ FIRST APPARENT EL = 4,370 METERS. Using the GST, set +60 underneath the MHL on the D scale. Move the site-range scale for charge 4GB TAG until range 4370 is underneath the MHL. Read site underneath the M gauge point on the D scale.
Because the first and second apparent sites are within 1 mil, the last site determined, +15 mils, is the true site.
d. Determine the true adjusted elevation.
- TRUE SITE +15
TRUE ADJUSTED ELEVATION 257
RG ~ TRUE ADJ EL = 4360, which is the polar plot range.
e. Using the GST, determine the VI.
x TRUE SITE +15
VI +60
f. Determine the firing unit altitude.
- VI +60
FIRING UNIT ALT 340
The introduction of an estimated VI of +60 meters changes the polar plot range from the firing unit to the known point by 200 meters (4560 to 4360). The polar plot direction is determined as shown in paragraph 6-20.
6-28. Example of Time Plot, VI Unknown
How To Plot 8 Digit Grid Coordinates
| NOTE: Use the known data from paragraph 6-26. |
a. At the completion of the registration, the adjusted data areas follows:
Adjusted time (M582): 15.6
Adjusted deflection: 3346
Adjusted quadrant: 272
| NOTE: The adjusted data come from the example shown in Figure 6-24. |
b. Determine the angle of site.
NOTE: EL+ CAS ~ TO ADJ FS = 257. |
- EL + CAS 257
ANGLE OF SITE +15
c. Using the GST, determine the VI.
| NOTE: RG ~ ADJ FS = 4360, which is the polar plot range. |
x POLAR PLOT RANGE 4360 (C scale)
VI +64
d. Determine the firing unit altitude.
- VI +64
FIRING UNIT ALT 336
e. Determine the polar plot direction as discussed in paragraph 6-20.
6-29. Example of Time Plot, VI Known, XO's High Burst
| NOTE: Use the known data from paragraph 6-26. |
a. The site to crest from the XO's report is +32 mils for the registering piece. This example will demonstrate how to determine the HOB correction by using the 10-mil assurance factor.
b. Determine the asked for HOB correction.
+ ASSURANCE FACTOR +10
ASKED FOR HOB CORRECTION +42
c. Determine the XO's high-burst QE.
+ ASKED FOR +42
XO's HB QE 314
d. The computer announces orienting data to the XO or platoon leader.
e. Three rounds are fired, and the following angles of site are reported by the XO or platoon leader.
Round 1: SI +54
Round 2: SI +54
Round 3: SI +57
Avg SI: Determined by XO or platoon leader.
| NOTE: AVG SI = +55, which equals GOT. |
f. Determine the angle of site to the known point.
GOT +55
- ASKED FOR+42
SI TO KN +13
g. Using the GST, determine the VI.
| NOTE: RG ~ ADJ FS = 4360, which is the polar plot range. |
POLAR PLOT RANGE 4360
x ANGLE OF SITE+13
VI +56
h. Determine the firing unit altitude.
KN PT ALT 400
- VI +56
FIRING UNIT ALT 344
i. Determine the polar plot direction as discussed in paragraph 6-20.
6-30. Locate an Observer
If the observer is equipped with a laser, his location may be established by resection. The procedures are listed below.
a. The observer lases the known point and determines a direction, distance, and a vertical angle. These are reported to the FDC.
b. The HCO determines the observer location as follows:
- Polar plots the back azimuth to the known point.
- Inserts a plotting pin along the back azimuth at the announced distance.
- Constructs a tick mark and labels it with the observer's call sign.
c. Using the GST, the VCO determines the observer's VI as follows:
- Places the M gauge point opposite the VA on the D scale.
- Moves the MHL over the distance on the C scale.
- Reads the VI under the MHL from the D scale.
d. To determine the observer's altitude, subtract the VI from the known point altitude.
6-31. Battalion Observed Firing Charts
a. Battalion observed firing charts are based on the concept that if any two points can be located by reference to a third point, the two points can be located in reference to each other. All batteries register on the same known point. For example, using the techniques for battery or platoon observed firing charts discussed in Section II of this chapter, firing units can be located in relation to the known point. After all the firing unit locations are plotted on a single firing chart in relation to the known point, the firing chart provides an accurate graphical representation of the location of the firing units in relation to each other. (See Figure 6-28.) This accurate portrayal of the relationship among the firing unit locations allows for the accurate massing of fires within the battalion on any target located by adjustment of one of the firing units, or by a shift from a known point (known to all firing units).
b. The techniques used in the construction of a battalion observed firing chart are very similar to those used for the construction of a single firing unit observed firing chart. The direction used for polar plotting each firing unit is determined by using the same procedures as the battery or platoon observed firing chart.
(1) Percussion Plot, VI Unknown. Range and altitude may be determined for each firing unit by using the procedures in paragraph 6-21. The accurate massing of fires is not possible when this method is used.
(2) Percussion Plot, VI Estimated. Range and altitude for each firing unit may be determined by using the same procedures listed in Table 6-10. If the relative altitude of the firing units can be estimated, the accuracy of the firing chart can be improved. One firing unit is selected as a reference unit and is assigned the same altitude as the known point. The vertical intervals of the other units are estimated and compared with the altitude of the reference firing unit to obtain their altitudes.
(3) Time Plot. Range and altitude for each firing unit may be determined by using the same procedures listed in paragraphs 6-23 and 6-24. This provides a more accurate means of determining relative location. One firing unit is selected as a reference unit. The vertical intervals of the other firing units are estimated and compared with the altitude of the reference firing unit to obtain their altitudes.
6-32. Observed Firing Chart With Incomplete Survey
a. A position area survey maybe used in conjunction with the observed firing chart until the surveyed firing chart is available. The part of the chart established by firing must be plotted to the same scale as the part obtained by survey.
b. The procedure for constructing a battalion observed firing chart that is based on the registration of one unit and that has position area survey is listed in Table 6-14.
Section V
Using Map Spot Data to Construct Firing Charts
The surveyed location and azimuth of lay should be established as soon as possible. Surveyed locations can be determined by map spot survey or by normal survey procedures. Map spot is less accurate than actual survey. If survey teams cannot immediately provide the needed data, the firing unit conducts a map spot survey to establish the unit center and azimuth of lay. For a map spot survey, fire direction personnel use hasty survey methods to associate terrain features with the locations of those features on a map and to locate the unit's center in relation to the terrain features.
6-33. Map Spot Survey
Plot A 8 Digit Grid
a. Map spot survey is the application of basic map and terrain association. It should be as accurate as possible. Three-point resection is the preferred technique for establishing the unit center by map spot survey. The map spotted location of the unit center will include an eight-digit grid coordinate and an altitude in meters.
b. Directional control (an orienting station and the direction to the end of the orienting line [EOL]) also must be provided. Common directional control should be established as soon as possible, preferably by simultaneous observation or directional traverse during daylight or by Polaris-Kochab method at night. If none of these procedures can be done quickly, the firing unit must be laid magnetically.
| NOTE:FM 6-50 includes a detailed discussion of hasty survey techniques. |
6-34. Constructing a Firing Chart From Map Spot Survey
Plot 8 Digit Grid Military Map
a. To construct a firing chart based on map spot survey, the FDC must have three items of information:
- Assumed grid coordinates of the firing unit center.
- Assumed altitude of the firing unit.
- Assumed azimuth of lay.
b. When met + VE techniques cannot be used, the firing unit will register as the situation permits.
c. A firing chart based on map spot survey is only as accurate as the following:
- The map spotted location of the unit center and the known point.
- The azimuth of lay.
- The construction of the chart.
d. When a firing chart based on map spot survey is used, the orienting angle must be recorded when the firing unit is laid. This orienting angle is used to determine the actual azimuth of lay when directional control is provided.
e. The FDC replots all fired targets.
6-35. Transferring to a Surveyed Firing Chart
a. When the position and target area surveys are completed, the FDC is provided the following information:
How To Plot 8 Digit Grid
- Firing unit center grid coordinates and altitude to the nearest 0.1 meter and azimuth to the EOL to the nearest 0.1 mil.
- Known point coordinates and altitude to the nearest 0.1 meter.
b. The surveyed firing chart is constructed to show the accurate locations of the firing unit center, the known point, and the actual azimuth of lay.
c. The firing unit was initially laid, and the orienting angle was recorded. When the surveyed azimuth to the EOL is determined, the actual azimuth of lay is computed by using the following formula:
SURVEYED AZ TO EOL - ORIENTING ANGLE = AZ OF THE LINE OF FIRE.
d. The initial (map spot) azimuth of lay may be inaccurate. The actual azimuth of the line of fire may differ from the surveyed azimuth of lay. When survey data are provided, the FDC must--
- Construct a surveyed firing chart.
- Compute GFT settings.
8 Digit Grid Coordinate
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