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Land Nav Task 12 - Locate an Unknown Point on a Map and on the Ground by Intersection

Created by: Team Quinstreet
Posted : Monday January 01, 1900

Standards: Determined the 100,000-meter square identification letters and six-digit coordinates of the object or terrain feature to within 100 meters.

Conditions:
Given a standard 1:50,000-scale military map
of the area, the location of two known
points, a compass, a straight edge, a
coordinate scale, a protractor (GTA
05-02-012), a pencil, and an object or
terrain feature for which the soldier must
determine the grid location.

Standards:
Determined the 100,000-meter square
identification letters and six-digit
coordinates of the object or terrain feature
to within 100 meters.

 

Performance Steps

1.  
Use the map and compass method
(figure C-35).



Figure C-35.
Location of an unknown point




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

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

b.
Locate and mark your position
on the map.

c. 
Convert the magnetic azimuth to
the unknown point (22 degrees); change
it to a grid azimuth. In the example,
the G-M angle used was 10 degrees
easterly, giving a grid azimuth of 32
degrees.

d.
Place the protractor on the
map, ensuring that the zero-degree
indication on the protractor is
pointing to the top of the map (north)
and the index point is placed center
of mass on your location (figure
C-36). Place a tick mark at the number
of degrees you want to plot. Draw a
line on the map from your position on
this grid azimuth (32 degrees).

e.
Move to or call a second known
position from which the unknown point
can be seen. Locate this position on
the map.

f.  
Repeat steps 1c and 1d.

g.
Where the lines cross is the
location of the unknown point.

2.  
Use the straightedge method
(when no compass is available) (figure
C-36).



Figure C-36.
Intersection without compass




a.
See task number, 071-329-1012,
Orient a Map to the Ground by Map
Terrain Association.

b.
Locate and mark your position
on the map.

c. 
Lay a straightedge on the map
with one end at user’s position (A) as
a pivot point, and rotate the
straightedge until the unknown point
is sighted along the edge.

d.
Draw a line along the
straightedge.

e.
Repeat steps 2b, 2c, and 2d at
position (B) and, to check for
accuracy, at a third position.

f.  
The intersection of the lines
is the location of the unknown point
(C).

Evaluation
Preparation: 

Setup:
In a field location, give the soldier a
standard 1:50,000-scale military map of the
area, a compass, a straightedge, a
coordinate scale, a protractor, a pencil, an
unknown point, and two points (at least 400
meters apart) from which to determine
azimuths to the unknown point.

Brief
Soldier: Tell the soldier to determine
the six-digit grid coordinates of the
unknown point.

Performance Measures

GO

NO
GO

1.  
Determined the six-digit grid
coordinates, to include the 100,000
meter square identifier of the unknown
point to within 100 meters.

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

 

 

STP
21-1-SMCT