Final Exam Theory Material Flashcards

1
Q

What is geomatics?

A

the discipline of gathering, storing, processing, and delivering spatially referenced info

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2
Q

List and define the 4 mathematical surfaces used to approximate Earths surface

A

1) Ellipsoid:
Semi major axis runs from centre to equator and semi-minor axes runs from center to the poles. This is due to the flattening at the poles caused by earths rotation

2) Sphere: simplification of earths shape

3) Geoid: a best-fit approximation of global mean sea level based on earth’s gravitational field (not continuous across earth)

4) Plane: 2D projection of earths surface

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3
Q

List a define the three types of north

A

1) Geodetic or ‘true’ north: Direction of a meridian of longitude that converges on the earth’s axis of rotation (z-axis of our datum)

2) Magnetic North: Direction indicated by magnetic compass, variable.

3) Grid north: north direction of a grid line on a map. May or may not match geodetic north depending on the map projection.

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4
Q

what does a parallel of latitude represent?

A

angular distance in dms of a point north or south of the plane of the semi-major axis

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5
Q

What does a meridian of longitude represent?

A

angular distance in dms of a point east or west of a chosen “0” location -> prime / Greenwich meridian

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6
Q

1 degree equals how many arc minutes? arc seconds?

A

60, 3600

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7
Q

What’s the relationship between radians and degrees?

A

1 rad = 180deg/pi

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8
Q

Whats the difference between a simple plane and a mapping plane

A

simple plane- small areas < 200 sq km, where neglecting curvature has negligible effects on measurements and results, are treated as “flat”. Often used for cadastral surveys and localized engineering and construction projects

mapping plane- mathematically rigorous projection of the ellipsoid earth to the desired “flat” surface. used for all Canadian federal and provincial surveying and mapping, and in most municipal/urban areas.

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9
Q

What is a datum?

A

a reference from which spatial measurements are made. A reference datum is a known and constant surface which is used to describe the location of unknown points on the earth.

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10
Q

What are some horizontal / geodetic datums?

A

NAD 1927. 1983, CSRS 1983, WGS84

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11
Q

What is the most commonly used vertical datum for land-based geomatics surveys?

A

Mean-Sea level / Geoid

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12
Q

What is Orthometirc height?

A

The vertical distance from the vertical datum (msl / geoid) surface to a point on Earths terrain (physical surface)

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13
Q

What are the three surfaces used for map projections ?

A

Cylinder
Cone
Plane

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14
Q

List the aspect surface used and the properties preserved and distorted for the following map projections;
a) UTM
b) Lambert Conformal
c) Albers Equal Area

A

a) Cylinder;
Shape: Preserved
Area: distortions increase away from CM
Distance: distortions increase away from CM

b) Cone;
Shape: Preserved
Area: some distortions
Distance: some distortions

c) Cone;
Shape: some distortion
Area: preserved
Distance: some distortion

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15
Q

When is the grid distance greater than the ellipsoid distance?

A

At the very edge of the UTM zone, just past the secant point, where the scale factor is > 1

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16
Q

The minimum number of satellites needed for accurate ground positioning.

A

4 Satellites

17
Q

Name the 4 error sources in GPS.

A
  1. Station Errors - Station coordinate errors or mulit-path
  2. Satelite Errors - orbit uncertainty and satellite clock error
  3. Reciever Errors - reciever clock error and reciever noise
  4. Observation Errors - ionospheric and tropospheric delay
18
Q

What are the 3 system components of GPS?

A
  1. User Segment
  2. Space Segment
  3. Control Segment
19
Q

How many hours does it take each satellite to orbit the earth?

A

12 hours per orbit (2 orbits per day in a 24h day).

20
Q

What are the benefits of using GPS?

A
  • Weather Independent
  • Does not require line of sight
    between ground points
  • Gives high Geodetic Accuracy
    – cm to mm accuracy
  • Can be operated day and night
  • In general, it is quicker and requires
    less manpower
    – Economical advantages
  • Common Coordinate System
    – WGS84
  • Wide Range of Applications
21
Q

Why are downsides of using conventional surveys?

A
  • Weather can limit operations (fog, rain,
    snow, etc.)
  • Rely on the line of sight between the
    survey instrument and a target
  • Usually limited to daylight field operations
  • Often requires specialized instrumentation
    and techniques
  • Generally requires two or more personnel
    for efficient field operations (often
    manpower intensive)
  • Achieving high accuracy and precision
    requires substantially more effort
  • Common coordinate system over large
    areas (City, Province/State, Country,
    Continent), but typical station separation is
    limited to 5 km or less.
22
Q

Russian version of GPS.

A

GLONASS

23
Q

What does GNSS stand for?

A

Global Navigation Satellite System

24
Q

Chinese and European GPS Systems?

A

COMPASS (Chinese) and GALLILEO (European Union).

25
Q

What are the 4 GNSS constellations and their country

A
  1. GPS - USA
  2. GLONASS - Russia
  3. COMPASS - China
  4. GALLILEO - EU
26
Q

What is the orbital path and period of GPS satellites?

A

Mid-earth near-circular orbit
12 hour period / orbits earth twice per day

27
Q

What does DOP stand for?

A

Dilution of precision

28
Q

what are several factors that introduce error to the accuracy of GPS positioning

A
  • Station Errors- Station Coordinates: failure to use appropriate receiver operating procedures such as using incorrect coordinates for base station.
  • Satellite Errors: These are errors introduced by orbit uncertainty and inaccuracies/drifting of time reported by the satellite clock.
  • Receiver Errors: These are errors introduced by inaccuracies/drifting of time reported by the receiver clock and by receiver noise.
  • Observation Errors: Occur as a result of ionospheric and tropospheric delay
29
Q

What reference ellipsoid is used for GPS? Which correction is applied to GPS height and why is it used?

A

WGS 84. The geoid height (N-value) is applied to GPS height (ellipsoid) to correct it to the elevation (H) of the topographic surface.

30
Q

To determine a reasonably accurate 3 dimensional (x,y,z) coordinate point location, how many GPS satellites are required and why?

A

Four- one for x-position, one for y-position, one for z-position, and one to adjust for the error in the receiver clock.

31
Q

List the main survey equipment components used for GPS positioning and their purpose.

A
  1. Antenna: to collect satellite signals
  2. Receiver: to process satellite signals
  3. Pole: to position precisely over poi and raise antenna to reduce signal obstruction
  4. Controller: to display, upload and download data
  5. Modem or radio: to allow for real-time communication link with reference or base stn.
32
Q

List several advantages of using GPS for spatial data acquisition compared to terrestrial survey methods. Give two examples where terrestrial survey methods
would be better suited?

A
  • weather and time of day independent
  • quicker
    -requires fewer human resources => more economic
  • enable common coordinate systems globally

Terrestrial surveys are better suited for local projects that require very high precision and accuracy, such are legal/cadastral surveys and surveys for engineering developments.

33
Q

What error sources does differential GPS reduce?

A
  • satellite and receiver clock errors
  • atmospheric delays