Lectures Flashcards
Geomatics defined
•Geomatics is a field of activities which, using a systemic approach, integrates all the means used to acquire and manage spatial data required as part of scientific, administrative, legal and technical operations involved in the process of the production and management of spatial information.
5 key parts of geomatics
measurement, analysis,
management, storage and display
spatial data
Directly or indirectly referenced to a location on the
surface of the earth
• Space / Place • Almost everything around us can be referred to as Spatial Answers: what is where? Where can something be found? Why something happens there, not elsewhere?
non spatial data
Cannot be related to a location on the surface of the earth is referred as non spatial data.
Describe differences between :
Geographic information systems
Spatial info systems
land information system
GIScience
Geographic information systems
• properly emphasizes geographic component
• minimizes computer science
Spatial information systems
•perhaps focuses too much on “information systems”
Land information systems
• deals with the cadaster
-land info for real estate
GIScience
•emphasizing computer science aspect (focusing on big data management, geo-visualization and incorporating both GIS,Remote Sensing
Data vs. Information
Data vs. Information:
. information is pulled from a pool of data
. data is the bare results
-when you play with data it becomes information
8 subject areas in geomatics
Surveying and mapping Geodesy and Gravimetry Land information management Positioning and navigation (GPS, GLONASS etc.) Cartography & digital mapping Geographic information systems Remote sensing (aerial/satellite/ground based) Photogrammetry
data from original GIS was stored on
Stored on magnetic tape (digital)
words transferred into numbers for storage
Geodesy
4 parts
A scientific discipline determining the shape,
size, rotation and gravity field of planet Earth,
including their variations in time.
Why is Geodesy important
• Accurate positions are required for a wide variety of
applications; including:
surveying, mapping and navigation, remote
sensing, mineral exploration, flood risk
determination, transportation, land use,
ecosystem management..
• Studying plate movement, subsidence of land, sea
level rise, movement of glacier and changes in
cryosphere………
Geodesy derived from greek words for _____ and the saying I devide and measure
derived from the Greek for ‘earth’ and ‘I divide and
measure’ and refers back to ancient Egyptian land
surveying techniques.
_______ believed the earth was flat in _th century bc while ______ in _th century bc realized it was spherical
_____ in ___ BCE was the one who truly got the sphere idea going
Homer-8
Pythagoras- 6
Aristotle (384 BCE)
Ancient Measurment of Earth:
• _______ made more
explicit measurements,
_______ miles.
Currently accepted
circumference is _______
miles
• Eratosthenes made more
explicit measurements,
25,000 miles.
Currently accepted
circumference is 24,901
miles
The Well Theory:
who came up with it?
What does it mean?
Eratostenes
.he realized when the sun is directly above a deep well in one city you could stand in a nearby city to the north and measure the angle of the shadows and multiply by the distance between the cities
shadow angle x distance= circumference
Geodesy was born
Two different types of remote sensing
Two different types of remote sensing:
.Active and inactive
.Active send energy towards an object allowing it to work at any time of day
. inactive uses the suns energy
Triangulation
(in surveying) the tracing and measurement of a series or network of triangles in order to determine the distances and relative positions of points spread over a territory or region, especially by measuring the length of one side of each triangle and deducing its angles and the length of the other two sides by observation from this baseline.
Equitorial Circumference=
Polar Circumference=
40,075 km
40,008 km
difference of 67 km
4 physical concepts affecting geodesy
Earths motions
Relationships in solar system
Plate tectonics
Gravity
Circle = ______
Real Shape of Earth=_____ / _____
Shape based on average water levels=
sphere
ellipsoid/spheroid
geoid
Ellipse->______/______ because of…
When the revolving oval is a perfect ellipse, the solid generated by the revolution is called the ellipsoid/ (Spheroid).
defining a spheroid
A spheroid is defined by either the semimajor axis, a, and the semiminor axis, b, or by ``a`` and the flattening. • The flattening f, is derived as follows: f = (a - b) / a • The flattening is a small value, so usually the quantity 1/f is used instead. • The flattening ranges from 0 to 1. A flattening value of 0 means the two axes are equal, resulting in a sphere.
describe the flattening
The flattening ranges from 0 to 1.
A flattening value of 0 means the
two axes are equal, resulting in
a sphere
Datum
• Datum is a reference point, surface, or axis
on an object against which measurements
are made
• A geodetic Datum is a reference from
which spatial measurements are made….
• A spheroid/ellipsoid approximates the shape
of the earth, a Datum defines the position of
the spheroid relative to the center of the
earth.
A mathematical surface (spheroid/ellipsoid) is used to approximates the shape of the earth, a Datum defines the position of the spheroid relative to the center of the earth.
define geodetic datum
A geodetic Datum is a reference from
which spatial measurements are made….
The international ellipsoid was developed by Hayford in ____ and adopted by the International Union of Geodesy and Geophysics (IUGG) which recommended it for international use.
1910
GRS80
A unified geodetic system for the whole world became
essential for several reasons:
advancement of space science and astronautics
lack of inter-continental geodetic information
need for global maps for navigation, aviation, and
geography and basis for a worldwide geo-data
• GRS80 was adopted by the International Association of Geodesy (IAG) in 1979.
• Become as origin of the WGS84 (World Geodetic
System), however, WGS84 refined afterword.
datum-coordinate system relationship?
• So, a Datum defines how a coordinate system is
seated over the ellipsoid/spheroid.
• The origin of the new NAD83 system is the centre
of mass of the Earth, and uses the ____ ellipsoid
GRS80
GPS receivers also use the centre of mass of the
Earth as their system’s origin, uses ______
system.
WGS84
NAD27
The old North American Datum 1927 (NAD27) had
a different origin, making it useful only in North
America.
T OR F
For all practical applications WGS84 ellipsoid and GRS80 ellipsoid are identical.
T
NAD83
looks to track the North American plate
Geoid
Is a Hypothetical Earth surface representing the
mean sea level in the absence of winds, currents,
and most tides;
• the arithmetic mean of hourly water elevations observed over a specific 19-year cycle, and defined as the zero elevation for a local area;
Geoid
Is a Hypothetical Earth surface representing the
mean sea level in the absence of winds, currents,
and most tides;
• the arithmetic mean of hourly water elevations observed over a specific 19-year cycle, and defined as the zero elevation for a local area;
.Geodesists once believed that the sea was in balance with the earth’s gravity and formed a perfectly regular figure;
.The Earth’s actual gravity field differs from the gravity field of a uniform, featureless Earth surface.
.Zero elevation as defined by Spain is not the same
zero elevation defined by Canada, which is why
locally defined vertical Datums differ from each
other.
The geoid surface cannot be directly observed;
• heights above or below the geoid surface can’t be
directly measured;
• How it is measured the?
inferred by making gravity measurements and
modeling the surface mathematically.
• Geoid is the equipotential surface of the Earth’s
gravity field which best fits, in a least squares
sense, global mean sea level- NASA
GOCE Satellite
GRAVITY FIELD AND STEADY STATE OCEAN CIRCULATION EXPLORER (GOCE)
Gravity field and steady-state Ocean Circulation
Explorer – GOCE– has mapped variations in Earth’s
gravity with unrivalled precision. The result is the
most accurate shape of the ‘geoid’ – a hypothetical
global ocean at rest – ever produced, which is being
used to understand ocean circulation, sea level, ice
dynamics and Earth’s interior.
Geoid + Ellipsoid relationship: deflection of the vertical
The angle between a plumb line (perpendicular to the
geoid) and the Normal line (the perpendicular to the
ellipsoid) is called as the “deflection of the vertical”
Geoid, Ellipsoid, and physical earth
Which one is a reliable reference for making extremely precise calculation of physical heights?
This drawing illustrates the differences between the elevation of the physical Earth surface and the ellipsoid, an equal geometric measurement from the Earth’s axis, and the geoid, which is based on equal gravity. Only the geoid is a reliable reference for making extremely precise calculations of physical heights.
Horizontal and Vertical Datums
Horizontal Datums are used for describing a point
on the earth’s surface, in latitude and longitude or
another coordinate system.
A vertical Datum are used to measure elevations
or depths.
• These are either based on sea levels or geoid and use the same ellipsoid models of the earth used for
computing horizontal Datum.
CGVD2013
replaces CGVD__
• The Canadian Geodetic Vertical Datum of 2013
(CGVD2013) was officially released in November 2013
representing by convention the coastal mean sea level
for North America.
• It replaces the Canadian Geodetic Vertical Datum of
1928 (CGVD28).
CGVD28 is a tidal Datum defined by the mean water
level at five tide gauges: Yarmouth and Halifax on the
Atlantic Ocean, Pointe-au-Père on the St-Lawrence
River, and Vancouver and Prince-Rupert on the Pacific
Ocean.
T OR F
The change in Datum will not cause a shift in every position on the map
F
T OR F
It is best to use the WGS 84 Datum, especially for GPS, unless it is required to use a local system.
T
What is a coordinate system? and the 3 types
a system which uses one or more numbers to uniquely determine the position of a point or other element within a space. • The properties that define a coordinate system are Definition of axis –number, name, order/sequence Definition of measurements – unit, direction (positive/negative),
- Observer based – azimuth and altitude
- Earth based – latitude and longitude
- Celestial – declination and right ascension
(or sidereal hour angle)
Over Eat Cereal
Zenith
Zenith Point directly above the observer
=90 degrees
Nadir
Nadir point directly below the observer; can’t be seen -90
Horizon
Horizon Plan
0
Azimuth
Azimuth Angle from true north (clockwise) to the perpendicular arc from star to horizon 0 to 360
Altitude angle
Altitude Angle above the horizon to an object (star, sun, etc) 0 to 90
Earths Rotation
Counter clockwise direction (if you see it from north pole) • One rotation take a solar day (24 hours) • Provides an axis connecting north and south poles • Provides the basis for a system to determine location • Geographic coordinate system or geographic grid
Geographic Grid
• Network of lines – east – west (parallels) – north – south (meridians) • Surface of the earth is curved – Grid is not rectangular or square • Circles and half circles – Parallels and meridians
Parallels define degrees latitude
relative to the equator
Meridians define degrees longitude
relative to the prime meridian
Construction of paralells
• Starting point is the axis of rotation • Equatorial plane – Imaginary plane through center of the earth – Perpendicular to the axis of rotation • Latitude – The angular distance towards north or south of the equator from the equatorial plane – 00 at the equator and +900 at the North pole and -900 at the South pole
small circles
Circles produced by a plane passing through a
sphere anywhere except its center are referred to
as small circles. All parallels except the equator are
small circles
Geometric Datum
Geometric Datum: records both of above and the UTC(COORDINATED UNIVERSAL TIME)
-time is changing with location and orientation
The two properties that define a coordinate system are
. The properties that define a coordinate system are
- definition of axis: number, name, order/sequence
- definition of measurements: unit, direction (positive/negative)
Great circle
Great Circle:
. if a sphere is divided exactly in half by a plane passing through its centre, the intersection of the plane with the sphere represents the largest circle that can be drawn on a sphere
- Great circles are the largest circles that can be drawn
on a spherical surface - An infinite number of great circles can be drawn on a
sphere - Only one great circle can be drawn to pass through
two points on the surface of a sphere – unless
–the two points are the ends of the same
diameter - An arc of a great circle is the shortest distance of two
points on the surface of a spheroid
Equation to find distance of travel along a parallel
(COS(LATITUDE IN DEGREE) x 111)/ DEGREE OF LONGITUDE
• Example: Vancouver and Winnipeg are separated
by 260 longitude. If both city are on at 490N, what is
the linier distance between them?
[cos (49) = 0.656 ]
construction of meridians
Construction of meridians • Meridians are halves of great circles • Extend from north pole to south pole • No convenient place to start • Arbitrary starting point Meridian passing through Greenwich, England is the 0 meridian or prime meridian • Longitude Angle between prime meridian plane and the meridian plane from the point of interest.
Longitude also express in degrees, minutes and seconds Indicate east-west position West of prime meridian: W East of prime meridian: E Prime meridian 0 degrees Meridians are between 0 degrees -180 degrees Western hemisphere Eastern hemisphere
Along a meridian is approximately ____ km
• Along the meridian (north-south)
= Earth’s Circumference/360
= 111 Km (approx.)
T OR F
along a parallel is approximately 111 km
F
• Along the parallel (east-west)
= depends of the latitude
= cos(latitude in degree) * (111)
• Example: Vancouver and Winnipeg are separated
by 260 longitude. If both city are on at 490N, what is
the linier distance between them?
[cos (49) = 0.656 ]
projection
is a method of transferring features of the spherical Earth to a flat surface
• Map Projections define the spatial relationship between locations on earth and their relative locations on a flat map
A method of projection provides an orderly system of parallels and meridian that is used to model the relative location of earth surface features on a two dimensional media
three steps in makeing a map projection
- a transparent globe with geographical grid
and may be continents are drawn on it - a light source placed inner side (center…) of
the globe - a paper placed on the surface of the globe in
flat or conical or cylindrical shape
Three main types of projections:
Planar= North and south pole
Conical:
Cylindrical: mercator
explain conic secant vs tangent
A cone is placed over a globe. The cone and globe meet along a latitude line. This is the standard parallel. The cone is cut along the line of longitude that is opposite the central meridian and flattened into a plane.
A cone is placed over a globe but cuts through the surface. The cone and globe meet along two latitude lines. These are the standard parallels. The cone is cut along the line of longitude that is opposite the central meridian and flattened into a plane.
what is the standard parrallel?
where measurements most accurate on projection
ARCGIS supports __ different map projections
66
T OR F
Mercator is the best map projection
F
No best projection
no projection can preserve all 5 of these features
angle, direction, distance, shape, area
On a map, the direction is correct means the
bearing between two points is correct on anywhere
on the map
If a projection preserves shape and area on the
map, an area is uniformly proportional to the real
world that they represent.
5 different types of projections: Not the shape, just different kinds
• Conformal Projection – preserves the correct shapes of small areas.
• Equal Area Projection - quadrilaterals formed by
meridians and parallels have an area on the map
proportional to their area on the globe.
• Equidistant Projection - distance from a single location
to all other locations are preserved.
• Azimuthal Projection– directions from a single location
to all other locations are preserved
• Compromise Projection - attempt to balance between
the above characteristics, and is often used in thematic
mapping.
Chelsea eats everything at christines
Gerardus map is a ______ projection shape
Lambert map is a ______ projection shaoe
Transvers mercator mao is a ______ projection shape
- Mercator (Cylindrical)
- Lambert conical conformal (Conical)
- Transvers Mercator (transvers Cylindrical)
______ is an example of a map projection that cannot be classified by shape because it is a mathematical description
Goodes
Gerardus map described
• a cylindrical projection with rectangular
grid
• Distance between parallel increase with latitude
• Polar cut-of at 800 N and 800 S
• High distortion of shape and area toward pole,
e.g.: Greenland shows same size as Africa
• Scale on 600 latitude is 2 times (on 800, it 6X)
of that on the equator
• Impotent properties preserves direction (bearing), which makes it Indispensable for navigation
• Other uses to show linier features like wind flow line, ocean currents, global temperature and pressure patterns.
Polar Projection
Can be centred on either the North or South Pole
• Meridians are straight lines radiating outward from the pole
• Parallels are nested circles centred on the pole
• Parallels with the meridians intersect at right angles
• The space between the parallels increases outward from the
centre
• shows the true shapes of small areas,
such as islands
• Scale increases away from the centre
• shapes look disproportionately larger
toward the edge of the map
Goodes Projection
uses two sets of mathematical curves to form its meridians
. between 40th parallels, it uses sine curves
.beyond the 40th parallel, toward the poles it uses ellipses
.ellipses converge to meet at the pole so the entire globe can be shown
.commonly used to show regional distributions of geographical features, such as soils and vegetation
.shows area in correct proportion
.distorts the shapes of areas particularly in high latitudes
For map of canada the best is generally _____ conical conformation projection
Lambert
WGS84
• WGS84 (World Geodetic System of 1984) - geodetic
coordinate reference system (datum) developed and used by GPS. no physical monuments.
NAD83
• NAD83 (North American Datum of 1983) - developed
based on GRS 1980
the ellipsoid defined through the use of satellites.
tied to the North American tectonic plate, meaning that
over time it diverges from WGS84
currently by ~1 m depends on where you are
4
NAD27
NAD27 (North American Datum of 1927) - developed
based on the Clarke Ellipsoid of 1866.
- discontinued from use but there are still quite a few GIS
datasets with it.
- its coordinate difference from NAD83 depends on the location
- ~20 m around Thunder Bay.
Three most common datum types used in canada
NAD27, NAD83, WGS84
tRANSVERSE MERCATOR
Whole Earth Can be shown, but all distances, directions, shapes, and areas are reasonably accurate within 15°of the central meridian.
• Distances are true only along the central
meridian selected by the mapmaker or
else along two lines parallel to it;
Whole Earth Can be shown, but all
distances, directions, shapes, and areas are reasonably accurate within 15°of the central meridian.
Distances are true only along the central
meridian selected by the mapmaker or else along two lines parallel to it;
This is an ellipsoidal cylindrical projection that divides the world into numbered zones in longitude.
60 longitudinal projection zones numbered 1 to 60 starting at 180°W.
Each zone is 60 wide (with a few exceptions). Each zone has a central
meridian
UTM
Whole Earth Can be shown, but all distances, directions, shapes, and areas are reasonably accurate within 15°of the central meridian.
Distances are true only along the central meridian selected by the mapmaker or else along two lines parallel to it;
This is an ellipsoidal cylindrical projection that divides the world into numbered zones in longitude.
60 longitudinal projection zones numbered 1 to 60 starting at 180°W.
Each zone is 60 wide (with a few exceptions). Each zone has a central
meridian
20 latitudinal zones from 80°S to 84°N denoted by letters C to X, omitting the letters I & O.
Each zone is 80 south-north (except the
zone “X” is 12°).
Areas are referenced by quoting the longitudinal zone number, followed by the latitudinal zone letter
• UTM projection use easting and northing in
metres for coordinates.
• The central meridian’s coordinate is always
500,000;
• The Equator’s coordinate is designated 0 for
quadrangles in the northern hemisphere;
• UofS Campus Bowl is at 388,515 Easting
5,777,209 Northing
The central meridian’s coordinate is always 500,000;
• The Equator’s coordinate is designated 10,000,000
for quadrangles in the southern hemisphere; Since the distance from poles to Equator is approximately
10,000 km, such offset origins ensure coordinates (the false eastings and false northings) are always positive.
Each zone is separately projected using the ellipsoidal form of the transverse Mercator projection with a secant case: scale of the central meridian is reduced by 0.04%, so two lines about 1°37” east and west of it have true scale. The UTM grid was designed for largescale
topographic mapping in separate sheets, not for world or regional maps. In particular, sheets from different zones don’t juxtapose exactly.
