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.
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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
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
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