1 Flashcards
what is gps?
“Global Positioning Service”, specific version of a global navigational satellite system (GNSS), satellites orbiting the earth transmit electromagnetic signals to receivers
what are the components of gps?
user segment (receiver picks up signal and use info to calculate location)
control segment (network of on ground stations which check on position and speed of satellites, master control in Colorado)
space segment (31 satellites orbiting earth, 6-12 generally visible at any unobstructed location, they send out radio signals every minute with date and positioning info)
what is selective availability?
A process by which the accuracy of GPS systems was purposefully degraded to ~100m (~15m accuracy initially reserved for military use), removed in May 2000
what is the difference between latitude and longitude?
Latitude goes around, distance from equator. Longitude goes up and down, distance from prime meridian.
Latitudes are always parallel, meridians converge at the poles
what is a map projection?
A systematic arrangement of the geographic coordinates of a 3-D spherical earth onto a 2-D plane
what is a geoid?
Model of global mean sea level based on measurements of earth’s gravitational field
Irregular shape due to variations in the density/thickness of earth’s crust which cause differences in gravitational force
Geoid is an interpolated surface based on gravity
what is an ellipsoid
Squashed circle, mathematical model that smooths the irregular shape of the geoid. The squished shape is due to the earth’s gravitation and rotation.
how do you convert into and out of degrees, mins, secs
ddd° mmm’ sss” to ddd.dddd°
e.g. A° B’ C” = A + (B/60 + C/3600)°
ddd.dddd° to ddd° mmm’ sss”
e.g. A.aaa° = A° (aaa*60)’ etc
divide to go from deg min sec to decimal deg
multiply to go from decimal deg to deg min sec
what are developable surfaces? name three types
Planar, cylinder, conic, can have tangent case or secant case
Developable surface flattens to form a plane, original surface does not compress or stretch
different types of datums, what they are and why we use them?
Use information about the earth from ellipsoid (horizontal) and geoid (vertical).
Provides a starting point (origin) for mapping
Use a mathematical model to fit the coordinate system (Lat Long) to
the surface of the earth.
Common types are WGS84, NAD83, and NAD27
some datums are highly localised, so are designed on a global scale
difference between geographic coordinates (systems) and projected coordinate (systems)
for projected coord systems like UTM each zone uses its own secant Mercator projection (large area, low distortion) used in 2D, geographic cords are based on 3D
what are 4 issues with gps accuracy and degradation
number of error types that can affect accuracy:
blocked signals (dense buildings, trees, degraded position accuracy or inability of receiver to determine position, may not be able to get 4 signals)
reflected signals
ionospheric interference (signal refracted, accounts for 5-15m of gps error)
satellite geometry (satellites too close together, more satellites = lower gdop = better accuracy, geometric dilution of precision)
what are standard points/lines?
A line(s) or point on a map that has the same scale (dimensions) as the reference globe
* Why are they important?
* No scale distortion
* The farther from the standard line/point the more distortion
projection properties and aims
Projections aim to preserve specific geographic properties:
* Areas (equal area)
* Angles / Shape (conformal)
* Distances (equidistant) - *from one to all other points, or between selected points
* Directions (azimuthal) - ** from a point, never global, not exclusive
All maps are distorted somehow, impossible to turn a sphere into a flat map without distortion
trilateration
You need at least three known distances from known locations to find your location.
Given this information you can pinpoint your location: where the distances intersect
3 satellites will give 2d location, 4 satellites will give 3d location (elevation)
differences between accuracy and precision
Accuracy: a measure of nearness to correct value, measurement close to true value
Precision: a measure of exactness; more decimal places = more precise, measurements close together
describe evolution of how accurate GPS receivers are
only accurate to ~100m until selective availability removed in 2000, then ~15m accuracy, now typically around ~10-15m accuracy, better accuracy on phone due to info from cell towers etc
what is NAD83? what is WGS84?
NAD83 is a 1983 local north American datum i.e., ellipsoid is “tied” to earth’s surface around north America.
WGS84 or “world geodesic system” is a global datum based on the WGS84 ellipsoid, the most accurate global ellipsoid, ellipsoid tied to centre of earth
geocaching producers consumers, differences
Consumers: find geocaches, post their experiences online
Producers: players generate the content of the activity rather than relying on third-party content developers.
It is the users’ responsibility to maintain geocaches
components and sub-components of geocaching
physical infrastructure
online infrastructure (central website providing: location for listing of geocache coordinates and supplementary info about each cache, online forum for people to record their experience, provides feedback to cache owner, helps maintain quality/accuracy issues, and Volunteer ‘reviewers’ do an initial check on the general
appropriateness of the cache location before approving the listing, Online logs from users help to maintain quality/accuracy)
users
what geocaching offers, positives and potential negatives, why its popular
positives
Unique way to share local knowledge (in the form of a physical location)
Gets people outside/active
Allows people to explore/discover their own area
Spatial awareness
As with other location-based experiences, geocaching helps create a sense of place from a particular space
Fun
Economic opportunities (e.g., geocache tourism)
negatives
Safety – if hidden in dangerous locations
Privacy: Geocaches on private property
Environmental issues – impact of repeated searching, poorly chosen hide locations
How to manage the activity? Should it be managed?
common geocaching acronyms
DNF - did not find
BYOP - bring your own pen
CITO - cache in trash out
FTF – First To Find
TFTC – Thanks for the Cache
TFTH – Thanks for the Hide/Hunt
TNLN – Took Nothing, Left Nothing
TNLNSL - Took Nothing, Left Nothing, Signed Logbook
types of geocache
Traditional cache - watertight container containing Logbook, Pen and Trade items
Micro caches – tiny containers (film canister or smaller)
Multi-caches – series of clues or containers that lead to final cache
Mystery/Puzzle caches – users must complete certain tasks or solve puzzles in order to find the coordinates for the cache
Virtual caches – no physical container exists; instead, users find a specific piece of information at a given location
Earthcaches – instead of a physical cache, users visit a geological formation at a given location.
place vs space
Identity
* Relational and contextual
Place in/dependence
* What separates the place from the space
Affect
* A state of mind and body; emotions and feelings are just one part
* Difficult to describe as a physical and cognitive embodiment
space vs place akin to house vs home
history of satellite systems (TRANSIT, NAVSTAR)
1940’s, LORAN (Long Range Navigation)
- Terrestrial-based radio navigation system for ships and aircrafts (now obsolete)
- Accuracy in the range of ~100-500 metres
1964, TRANSIT, first locational system
- User had to be stationary
- Limited satellite coverage (often had to wait 35-100 min for a satellite to pass)
- No elevation or speed data available
- Accuracy limited to 200-500 m
1970’s, NAVSTAR (Navigation System with Timing and Ranging)
- Idea was to create a continuous positioning system that could be used anywhere in the world, under any conditions.
- Designed for military applications; eventually made available for civilian use.
Applied GPS, what are some ways we use this?
GPS on our cell phones, in our cars
Facebook check-ins
Geotagged photos on Flickr & GoogleEarth
Snapchat Map
Twitter
geo ethics?
Geosurveillance: tracking and watching where you go
Geoslavery: use of geosurveillance to control people
Citizen science?
Citizen science: GPS data collected by amateurs for science
* Bird monitoring
* Phenology
* Forest fires (fuel loads)
* BikeMaps.org
VGI: user-generated maps and geographic information
* Geotagged photos on Flickr and GoogleEarth
* GPS hiking and biking trails
* OpenStreetMap
* WikiMapia
Dobson and Herbert (2021), geoprivacy concerns?
without broad specific regulations limiting
location data collection and use—including a universal protected right for individuals to pursue anonymity—governments, commercial enterprises, employers, and individuals increasingly will exploit tracking technologies at the expense of geoprivacy.
The benefits of smartphones, GPS, social media, and other technologies are accepted for their conveniences with adverse acceptance of their risks and without a rigorous examination of potential means to balance benefits with risks.
people are happy to use their smartphones without too much concern about their geoprivacy
Ucar et al (2014) – Standard GPS units accuracy and use for science
The average area of agreement was ~93 per cent during the winter season, and ~84 per cent during the summer season.
Ranking of receivers by average area during
each season did not reveal significant problems within the set of receivers tested. In conclusion, data collected during each season were not significantly different.
