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