Resection
Resection is the method of locating one's position on a map by determining the grid azimuth to at least two well-defined locations that can be pinpointed on the map. For greater accuracy, the desired method of resection would be to use three or more well-defined locations.
a. When using the map and compass method (Figure 6-18)—
(1) Orient the map using the compass.
(2) Identify two or three known distant locations on the ground and mark them on the map.
(3) Measure the magnetic azimuth to one of the known positions from your location using a compass.
(4) Convert the magnetic azimuth to a grid azimuth.
(5) Convert the grid azimuth to a back azimuth. Using a protractor, draw a line for the back azimuth on the map from the known position back toward your unknown position.
(6) Repeat 3, 4, and 5 for a second position and a third position, if desired.
(7) The intersection of the lines is your location. Determine the grid coordinates to the desired accuracy.
Figure 6-18. Resection with map and compass.
a. When using the straightedge method (Figure 6-19)—
(1) Orient the map on a flat surface by the terrain association method.
(2) Locate at least two known distant locations or prominent features on the ground and mark them on the map.
(3) Lay a straightedge on the map using a known position as a pivot point. Rotate the straightedge until the known position on the map is aligned with the known position on the ground.
(4) Draw a line along the straightedge away from the known position on the ground toward your position.
(5) Repeat 3 and 4 using a second known position.
(6) The intersection of the lines on the map is your location. Determine the grid coordinates to the desired accuracy.
Figure 6-19. Resection with straightedge.
Modified resection is the method of locating one's position on the map when the person is located on a linear feature on the ground, such as a road, canal, or stream (Figure 6-20). Proceed as follows:
a. Orient the map using a compass or by terrain association.
b. Find a distant point that can be identified on the ground and on the map.
c. Determine the magnetic azimuth from your location to the distant known point.
d. Convert the magnetic azimuth to a grid azimuth.
e. Convert the grid azimuth to a back azimuth. Using a protractor, draw a line for the back azimuth on the map from the known position back toward your unknown position.
f. The location of the user is where the line crosses the linear feature. Determine the grid coordinates to the desired accuracy.
Figure 6-20. Modified resection.
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