COMPASS AND PACING
And GPS
ORIENTEERING AND SURVEYING
Determine area of land
Locate boundaries on map
Plot trails
Follow directions to a point
How accurate is needed?
COMPASS
Today’s
liquid-filled
field
compass,
when held
level and
read
properly is
accurate to
the nearest
2 degrees
STAFF COMPASS
More stable
Bubble level to insure horizontal orientation
Larger circle with finer scale
Accurate to nearest .5 degree
THEODOLITE
Tripod mounted for maximum
stability
Dual axis bubble levels
Large scale with magnified optics
Also measures vertical rise/drop
by sighting the same height on a
range pole held at the target
Most accurate non-electronic
method
Barely used today
LASER THEODOLITE
Sights at reflector at target
Does the horizontal distance
correction for you
GPS SURVEYING
Does not require line of sight between
antennas
Communicate wirelessly
Gets X,Y,Z coordinates of stations just
subtract the height of the unit
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.
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 had 100
links, and the link is used as a subdivision of the 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. A square that is 1 acre in area is roughly 200 feet on a
side (208.7’)
 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 mile = 5280 feet
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)
Quadrangle
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
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
A word about GLONASS
GLONASS (GLObal NAvigation Satellite System) is the Russian military equivalent
of the US GPS system. After launching in 1982 full capacity was reached in 1995
but allowed to decline until 2001, Under Putin, restoring this system was made a
priority. In 2010 Russian coverage was restored and by 2011 global coverage was
achieved. In 2015 smartphone chipsets have been enabled to receive GLONASS
signals.
GLONASS satellites orbit make them especially suited for usage in high latitudes
(north or south). US GPS coverage is better at lower latitudes, thus supplementing
GPS signals with GLONASS signals in Alaska and Canada is advantageous. In fact,
as of 2015 the GARMIN GPS that the USFS uses now is required to support both.
By utilizing both systems, accuracy in mountainous regions in high latitudes is
greatly improved and position fixes are quicker with more satellites available.
WHILE ON THE TOPIC…
 Other
countries have or plan to have
their own navigation system in place
 France has DORIS
 China has BeiDou – second edition
called COMPASS by 2020
 India has IRNSS (regional)
 The EU plans to have Galileo by 2020
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