land navigation and gps usage

Land Navigation and GPS Usage

Professional Military EducationInitial Entry Training

FM 3-25.26 Map Reading and Land Navigation

References

• Introduction• Map Coordinates• Determining Distance• Finding Correct Direction• Finding Your Position• Relief And Elevation• GPS Usage

Overview

To avoid getting lost, use:

· Map.

· Compass

· GPS

· Other ways to find directions

· Common sense

Land Navigation & GPS

Three things keep you from getting lost: · Finding your map coordinates· Determining distance· Finding the correct direction

Land Navigation & GPS

Finding Map Coordinates

A map is a drawing of earth's surface. Maps show natural and man-made objects by symbolsSymbols are explained in the lower left hand corner: "legend."

• Black lines running up and down (north and south) and crosswise (east and west).

• Lines form small numbered “grid squares”

• Using these numbers, you can identify each grid square.


• Read Grid Square numbers from left to right along the bottom

• Locate the line that borders the grid square on the left.

• Read up and find the east-west line that borders the grid square along the bottom


•82

•81

• Halfway between line 11 and line 12: first added number is 5 and the first half of your location is 115

• Three tenths of the way between line 81 and line 82; second half is 813.• Your location would be

115813.


The coordinate scale and protractor is a square piece of

clear, thin plastic which helps to measure small

distances inside grid squares.


• Maps drawn to scale, printed at bottom and top of the map.

• Scale 1:50,000 means 1 inch on the map equals 50,000 inches

• Use paper to mark the points between two points.

• Put paper beneath bar scales and read the ground distance in miles, meters, or yards.

Determining Distance

• Distance around a curve, use paper to make tick mark at start

• Pivot the paper around each curve and continue along the road's edge

• Repeat until you get to point B, following along the road's edge with your paper.

• Compare to scale


•9

•9

• Measure distance by counting paces. • Average person uses 116 paces for 100 meters. • Determine your paces on a 100-meter distance. • Rough terrain uses more paces, usually about

148 instead of 116.• Pace yourself over at least 600 meters of cross-

country terrain in order to determine paces• Know how many paces it takes you to walk 100

meters on both level and cross-country terrain


•9

•9

• Maintain a straight line by using a compass and steering points. At night, use compass and stars

• Figure only the straight-line distance when you have to walk around an obstacle.

• Keep count of the paces taken by using pebbles or knots (or beads) on a string: Put 10 pebbles in your right pocket.

• When you go 100 meters, move one pebble to your left pocket and start your count over.


• Azimuth is direction from one point to another, on map or on ground.

• Azimuths are given in degrees in a clockwise direction.

• 360 degrees in circle, so your azimuth can be any number up to 360o.

Finding Correct Direction

• Due east is 90o, due south is 180o, due west is 270o, due north is 360o

• Draw a line from your position to a location indicated ion the map.

• Line up the protractor with the 0o point on your position and the cross-center lines parallel with the grid lines.

• The line indicates the azimuth in degrees.


• To return to previous position, take a back azimuth by subtracting 180o from the first azimuth.

• If you cannot subtract 180o from your first azimuth because the number is less than 180o, then add 180o.


•9

•9

• Compasses indicate Magnetic North and maps indicate Grid North (based on flattening of round surface to flat map.)

• Grid North and Magnetic North are usually a few degrees off from True North.


•9

•9

• Difference in degrees between Grid North and Magnetic North is shown at the bottom of the map as the “G-M angle.”

• Newer maps shows how to change grid azimuths to magnetic azimuths and magnetic azimuths to grid azimuths.


• Use your compass to find or follow an azimuth.

• The compass arrow points towards magnetic north. Avoid any mass of metal such as a jeep, a truck, or electrical power lines.

•190o


• To shoot an azimuth, use the center-hold technique.

• Turn your entire body toward the object, point the compass cover directly at the object.

• Look down and read the azimuth from beneath the fixed black index line.

•190o


For more information, see FM 3-25.26 Map Reading and Land Navigation


Shadow-Tip Field-Expedient Method Step 1. Place a stick in the ground at a level spot where a distinctive shadow will be cast. Mark the shadow tip with a stone or twig. This is west.


Step 2. Wait 10 min. until the shadow tip moves a few inches. Mark the new position in the same way. This second shadow mark is always east. Step 3. Draw a straight line through the two marks to obtain an west-east line.


·Step 4. Stand with the first mark (west) to your left. The other directions are north to the front, east to the right, and south behind you. ·Step 5. Draw a north-south line perpendicular to the west-east line.


Watch Method

· In North temperate zone, point hour hand toward the sun. Your south line is midway between the hour hand and 1200 hours, standard time.

· If on daylight saving time, the north-south line is found between the hour hand and 1300 hours.


Watch Method

· In the South temperate, point the 1200 hour toward the sun, and midway between the 1200 hour and the hour hand will be your north line.

· If on daylight saving time, the north line lies midway between the hour hand and 1300 hours.


•17

Star Method • At night, locate north by finding

Polaris, the North Star• First, find the Big Dipper. • Last two stars of cup point at

Polaris, about 5 times out as the distance between those two stars.

• Facing Polaris, you are looking north, with east on your right and west on your left.

•Polaris

•North Pole


Resection• Orient map as closely as possible to

true north.• Find feature such as the water tower

(A) that you can find on map. • Put ruler on the map, place edge

right next to the water tower symbol (B).

• Align the ruler so that it points at the real water tower.

Finding Your Position

Resection• Draw a line along the ruler. • Find another feature such as the

road junction (C), and do the same thing.

• Lay ruler on your map and point it at the real junction (D)

• Draw another line along the ruler until it intersects the first line.

• The intersection is your location.


Modified Resection • If you know that you are located somewhere

along a certain linear feature on the map such as a road or riverbank, then you can use an easier method to pinpoint your location—a method called “modified resection.”

• First, orient your map. • Locate a feature that you can also find on the

map, such as water tower in previous example.


Modified Resection • Just as before, put a straightedge through the

water tower symbol on the map and align the straightedge so that it points exactly at the real water tower.

• Draw a line along the ruler. • The point where the line crosses the linear

feature you are on is your location.


Resection / Modified Resection• Use your compass, shoot

azimuths to your reference points, such as the water tower and the road junction.

• Convert magnetic azimuths to grid azimuths, determine grid back azimuths and plot them.

• Your position is where these grid back azimuths intersect.


Intersection• Intersection method used to find location of an

object that you can see in the distance, such as an observation post (OP), but is not on your map.

• Shoot an azimuth to the OP using your compass.• Convert the magnetic azimuth to a grid azimuth.


Intersection• Draw a line on the map from your location along

the grid azimuth. • Move to another location and shoot an azimuth.• Convert azimuth from magnetic to grid and draw it. • OP lies at the intersection,


• Some maps indicate elevation and relief: slopes, hills, and valleys.

• Check for hills and valleys along the direction you intend to travel before you start.

• Elevation of a point on the earth's surface is the vertical distance it is above or below sea level.

• Relief is the representation of shapes of hills, valleys, streams, or terrain features.

• Contour lines are the most common method used to depict relief and elevation of the terrain

Relief and Elevation

Contour Lines• Contour lines are brown lines.• Lines depicts height above sea level. • Contour interval is difference in

height (elevation) between lines• “A” is 80 feet lower than “B” • Every fifth line is heavier than the rest

and has a number for elevation.• Rate of rise or fall of terrain feature is

known as its slope.


• When the contour lines are close together at the top of a hill, the hilltop is pointed.

• The hilltop is flat when contour lines are widely spaced at the top.


• Contour lines across a stream come together in a V-shape.

• Map shows water as blue. • Contour lines determine the

direction that water flows• V-shape points upstream or

toward high ground. • Looking for a stream is a good

way to find valleys.


• Lower terrain between two hilltops is called a saddle.

• Saddle is represented as an hourglass shape.

• Going through a saddle is the easiest route to use to get beyond the two hills.


• A ridge is a fairly long, narrow section of terrain.

• Ground goes uphill in one direction, downhill in others

• Contour lines that form a ridge either U- or V-shaped.

• Closed end of contour line points away from high ground.


• Use contour lines to determine the line of sight.• Draw a line from point A to point B• Note that it crosses some contour lines with

higher elevation than both points. • You know you will not be able to see point B.


Earthmate GPS LT-40 (Tac-Pak)• Verify mapping application is

installed.• Plug device into a USB port on

your laptop computer• Configure the device with the

mapping application• Open the mapping application.

Using GPS Device

Earthmate GPS LT-40 (Tac-Pak)• Click the Options button on the

toolbar • Click the GPS Settings tab.• Select Earthmate or Generic from

Device drop-down list.• Select US6 in Port drop-down list.• Click Start GPS button in toolbar

Using GPS Device

Earthmate GPS LT-40 (Tac-Pak)• Light-emitting diode (LED)

indicates type of satellite info• Red: acquiring satellite

information.• Yellow: has a 2-D fix, no elevation

data available• Green: receiving sufficient satellite

information for full 3-D fix.

Using GPS Device

Questions?

Professional Military EducationInitial Entry Training

land navigation and gps usage

Documents

map reading

map equals

map coordinates maps

straight line

line u

eastwest line

grid square numbers

ground distance