### Compass and Pacing

```COMPASS AND PACING
And GPS
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.
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.
GUNTER’S CHAIN
 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
chain as a unit of length.
 In countries influenced 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
CHAINS
Conversions:
1 chain (1 ch) = 66 ft (100 links)
4 poles or rods = 1 chain
1 tally = 5 chains = 330 ft
20 chains = ¼ mile
80 chains = 1 mile
1 acre = 43560 square feet
640 acres = 1 section (square mile)
36 sections = 1 township
1 acre = 10 square chains
40 acres = 20 chains x 20 chains
1 section = 80 chains x 80 chains
‘THROWING’ THE CHAIN
HIPCHAIN
METES AND BOUNDS DEED SURVEYS
 Metes = distance to ‘turn’ of boundary
 Bounds = direction
 Historically 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?
PUBLIC LAND SURVEY SYSTEM
PLSS TERMS
dimensions
(miles) (mile2)
area
(acres)
(m2)
24 by 24
576
368,640
Township
6 by 6
36
23,040
Section
1 by 1
1
640
Half-section
1 by 1⁄2
1⁄
2
320
1,294,994
(km2)
notes
1,492 Usually 16 townships
93 Usually 36 sections
2.6
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
1.3
GPS
 Antenna
 Base map
 Record tracks, waypoints,
distance
WHAT IS GPS?
Global
 Positioning
 System

HISTORY OF GPS

Department of Defense developed for
 Standard
positioning service (public uses)
 Precise positioning service
Launches began in 1970s
 Full operational capability in mid 1990s
 ‘Selective Availability’ turned off 2000

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
 5 Monitoring
stations
 Ground control
stations (Ground
Antennas)

 Unmanned
 Enable
MCS to
control the satellites
USER SEGMENT
Antenna

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
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?
 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).

AREA DETERMINATION





Compass and Pacing
Map with dot grid
Cut and weigh method
GPS
ArcGIS or similar mapping software
```