Overview
The lecture explains how to use intersection and resection techniques with a map and compass to locate unknown points or your own position during land navigation.
Intersection Technique
- Intersection is used to determine the location of an unknown point visible from two or more known locations.
- At the first known point, obtain the magnetic azimuth to the unknown point with a compass.
- Convert the magnetic azimuth to a grid azimuth using the declination diagram.
- Draw a line on your map from your position along the grid azimuth.
- Move to a second known point and repeat the azimuth measurement and conversion.
- Draw another line from the second position; the unknown point is where the lines intersect.
Resection Technique
- Resection is used to find your own position when you can see at least two identifiable features on the map.
- Take a magnetic azimuth to the first known feature and convert it to a grid azimuth.
- Convert the grid azimuth to a back azimuth.
- Use a protractor to draw a line from the feature’s map location along the back azimuth.
- Repeat the process for additional visible features.
- Your location is where the lines cross.
Modified Resection
- Modified resection is used when you are on a linear feature (road, canal, or stream) and can see one identifiable object.
- Obtain the magnetic azimuth to the object, convert to grid azimuth, and then to back azimuth.
- Draw a line from the object’s map location; your position is where the line crosses the linear feature.
Best Practices
- Move carefully, focus, and take your time with each step to ensure accuracy.
- Slowing down and being precise will result in better navigation and timely completion.
Key Terms & Definitions
- Intersection — Method for finding the location of an unknown point using lines of sight from two or more known positions.
- Resection — Method for determining your own location by using lines of sight to at least two known map features.
- Azimuth — A compass bearing or angle measured in degrees from North.
- Grid Azimuth — An azimuth corrected for map grid north.
- Back Azimuth — The direction exactly opposite of the initial azimuth (add/subtract 180°).
Action Items / Next Steps
- Practice converting magnetic azimuths to grid azimuths using a map’s declination diagram.
- Use a protractor to draw azimuth lines on a map.
- Prepare for practical land navigation exercises using these techniques.