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Land Nav Task 13 - Locate an Unknown Point on a Map and on the Ground by Resection

Standards: Determined the 100,000 meter square identification letters and six-digit coordinates of your location to within 100 meters of the actual grid coordinates.

Conditions: Given an unknown location, a standard 1:50,000-scale military map of the area, a compass, a straightedge, a coordinate scale, a protractor (GTA 05-02-012), a pencil, and two terrain features visible from your location and identifiable on the map.

Standards: Determined the 100,000 meter square identification letters and six-digit coordinates of your location to within 100 meters of the actual grid coordinates.

 

Performance Steps

1.   Use the map and compass method (figure C-37).


Figure C-37. Using the map and compass


Note. The example map is not to scale-an easterly G-M angle of 10 degrees is used in the examples.

a. Determine the G-M angle of the map you are using.

b. Locate two known positions on the ground and mark them on your map (A, figure C-37).

c.  Using your compass, measure the magnetic azimuth to one of the known locations; change it to a grid azimuth (B, figure C-37.)

(1)  If it is a westerly G-M angle, subtract the number of degrees in the G-M angle from your magnetic azimuth.

(2)  If it is an easterly G-M angle, add the number of degrees in the G-M angle to your magnetic azimuth.

d. Change this grid azimuth to a back azimuth.

e. Place the protractor on the map, ensuring that the zero degree indicator on the protractor is pointing to the top of the map (north), and the index point is placed center mass on this location. Place a tick mark at the number of degrees you want to plot. Remove the protractor from the map and draw a line on the map from this position on the grid back azimuth you found, in the direction of your unknown position.

f.   Repeat steps 1c through 1e for a second (C, figure C-37), and third (D, figure C-37) known position.

g. Where these lines cross is your location.

2.   Perform resection without a compass (figure C-38).


Figure C-38. Resection without a compass


a. Orient your map as closely as you can using one of the ways you've learned about finding direction: compass, sun, watch, or stars. Then look for some feature, such a water tower (figure C-38, point A), that you can also find on the map. Put a ruler or straightedge on the map, and place its edge next to the water tower symbol (figure C-38, point B) on the map. Then align the straightedge so that it points directly at the real water tower. Draw a line along the straightedge or ruler (the line will cross the symbol for the water tower on your map).

Note. Do not move your map once it is properly oriented.

b. Find another feature, such a road junction (figure C-39, point C), and do the same things. Lay the straightedge on your map and point it at the real road junction, ensuring at the same time that its edge crosses over the road junction (figure C-39, point D) on the map. Draw another line along the ruler until it crosses (intersects) the first line. The point where the lines cross is your location. (figure C-39, point X) if you do this step with a third line, it may help location your position more accurately.


Figure C-39. Resection without a compass continued


3.   To perform modified resection you must be located on a linear feature such as a road, stream bank, railroad or ridge. First orient your map, then find some feature that you can also find on the map, such as the water tower in the previous example. Just as before, put a straightedge through the water tower on the map and align the straightedge so that it points directly at the real water tower. Draw a line along the ruler or straightedge. The point where the line crosses the linear feature is your location.

Note. Always orient your map as closely as you can. The compass is the best way to do so. If you don't have a ruler, use your rifle cleaning rod or a section of radio antenna as a straightedge.

Evaluation Preparation: 

Setup: Give the soldier a standard 1:50,000-scale military map of the local area, a compass, a coordinate scale, a protractor (GTA 05-02-012), a pencil, a straightedge, and the location of two known points.

Brief Soldier: Tell the soldier to determine the six-digit coordinates for his location.

 

Performance Measures

GO

NO GO

1.   Determined the six-digit grid coordinate and the 100,000 meter square identifier of the soldier's position (unknown point) within 100 meters.

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Evaluation Guidance:  Score the soldier GO if the performance measure is passed. Score the soldier NO GO if the performance measure is failed. If the soldier scores NO GO, show what was done wrong and how to do it correctly.

References

 

Required

Related

 

FM 3-25.26