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) (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

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.

China has BeiDou – second edition called COMPASS by 2020 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