And GPS COMPASS AND PACING. THE COMPASS I WANT TO GO NW First rotate the dial until it points the way you want to go Then rotate your body until the.

And GPSCOMPASS AND

PACING

THE COMPASS

I WANT TO GO NW

First rotate the dial until it points the way you want to go

Then rotate your body until the north arrow points north

Walk in the direction of the arrow

AZIMUTHS AND BEARINGS

COMPASSES AND MAPS

COMPASS APP

MAGNETIC DECLINATION

The declination is given as e.g. "15 degrees east". When you look at the figure, you can pretend that plus is to the right, or east, and minus is to the left and west. So when something is more than zero you'll subtract to get it back to zero. And if it is less, you'll add. So in this case you'll subtract 15 degrees to the azimuth, by turning the compass housing, according to the numbers on the housing.

ADDITIONAL CONSIDERATIONS

Compasses work underground unlike GPS

Local magnetic sources can cause errors

Can take a ‘backsight’ on where you came from to confirm that it is 180 degrees off the traveled azimuth.

Compass and Pacing is a conclave competition.

PACING

1 pace equals the natural stride of both legs starting and ending with the same foot.

Can and should practice often – get consistent.

Recognize that is varies by slope, must compensate.

In 1620, the clergyman Edmund Gunter developed a method of surveying land accurately with low technology equipment, this was 66 feet long and from the practice of using his chain, the word transferred to the actual measured unit. His chain had 100 links, and the link is used as a subdivision of the chain as a unit of length.

In countries infl uenced by English practice, land plans prepared before about 1960 associated with the sale of land usually have lengths marked in chains and links, and the areas of land parcels are indicated in acres. A rectangle of land one furlong (10 chains) in length and one chain in width has an area of one acre.

It is sometimes suggested that this was a medieval parcel of land capable of being worked by one man and supporting one family.

GUNTER’S CHAIN

GUNTER’S CHAIN

CHAINS

Conversions:1 chain (1 ch) = 66 ft (100 links)4 poles or rods = 1 chain1 tally = 5 chains = 330 ft20 chains = ¼ mile80 chains = 1 mile1 acre = 43560 square feet640 acres = 1 section (square mile)36 sections = 1 township1 acre = 10 square chains40 acres = 20 chains x 20 chains1 section = 80 chains x 80 chains

‘THROWING’ THE CHAIN

HIPCHAIN

Metes = distance to ‘turn’ of boundaryBounds = directionHistorically the original 13 colonies and their

derivative states (from the British surveying)

Problems: Described boundary points often change Doesn’t work well in homogenous landscapes Corrected for declination? Year surveyed?

METES AND BOUNDS DEED SURVEYS

PUBLIC LAND SURVEY SYSTEM

dimensions

(miles)(mile2

)

area(acres) (m2) (km2)

notes

Quadrangle 24 by 24 576 368,640 1,492  Usually 16 townships

Township 6 by 6 36 23,040 93   Usually 36 sections

Section 1 by 1 1 640 2.6

Half-section 1 by 1⁄2 1⁄2 320 1,294,994 1.3

Quarter-section 1⁄2 by 1⁄2 1⁄4 160 647,497

Half of quarter-section

1⁄2 by 1⁄4 1⁄8 80 323,749

Quarter of quarter-section

1⁄4 by 1⁄4 1⁄16 40 161,874

PLSS TERMS

AntennaReceiver

Base mapRecord tracks,

waypoints, distance

GPS

WHAT IS GPS?

Global Positioning System

HISTORY OF GPS

Department of Defense developed for navigation Standard positioning service (public uses) Precise positioning service

Launches began in 1970s Full operational capability in mid 1990s ‘Selective Availability’ turned off 2000

Degraded accuracy to ~100m

GPS SYSTEM SEGMENTS

Space segment – (satellite life = 10 years) Several generations of satellites in use now

Control segment User segment

SPACE SEGMENT 24 satellites with

spares in 6 orbital planes (4 in each)

~12,500 miles elevation

55 degree inclination

Each one circles Earth every 12 hours (7000 mph)

At least 4 visible at every point on the earth at all times

CONTROL SEGMENT Master Control

Station (MCS) in Colorado

5 Monitoring stations

Ground control stations (Ground Antennas) Unmanned Enable MCS to

control the satellites

USER SEGMENT

Antenna Receiver

Base map Record tracks,

waypoints, distance

HOW DOES IT WORK?

Triangulation

Need D+1 satellites to determine position = 2D needs 3 satellites, etc

SOURCES OF ERROR IONOSPHERE

Dual frequency mode of more advanced receivers corrects

SOURCES OF ERROR - SATELLITE GEOMETRY

Geometric Dilution of Precision (GDOP) – the higher the value, the poorer the measurement (very good = <4, bad = >6)

SOURCES OF ERROR MULTIPATH

HOW ACCURATE?

Recreation grade = ~8m Mapping grade = <1m Survey grade = several cm

Accuracy versus Precision Accurate measurement versus true

location Precise measurements close to each other

IMPROVING ACCURACY – 2 TO 5 M

CELL PHONE GPS

Most GPS in cell phones do not use satellites.

They triangulate via cell towers whose locations are precisely known.

The signal is not line-of-sight so they can work indoors.

Does not work where limited cell service exists (like many forests).

Accuracy varies (< 10 m to ~100 m).

Compass and PacingMap with dot gridCut and weigh methodGPSArcGIS or similar mapping software

AREA DETERMINATION