Final Exam Theory Material Flashcards
What is geomatics?
the discipline of gathering, storing, processing, and delivering spatially referenced info
List and define the 4 mathematical surfaces used to approximate Earths surface
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
List a define the three types of north
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.
what does a parallel of latitude represent?
angular distance in dms of a point north or south of the plane of the semi-major axis
What does a meridian of longitude represent?
angular distance in dms of a point east or west of a chosen “0” location -> prime / Greenwich meridian
1 degree equals how many arc minutes? arc seconds?
60, 3600
What’s the relationship between radians and degrees?
1 rad = 180deg/pi
Whats the difference between a simple plane and a mapping plane
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.
What is a datum?
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.
What are some horizontal / geodetic datums?
NAD 1927. 1983, CSRS 1983, WGS84
What is the most commonly used vertical datum for land-based geomatics surveys?
Mean-Sea level / Geoid
What is Orthometirc height?
The vertical distance from the vertical datum (msl / geoid) surface to a point on Earths terrain (physical surface)
What are the three surfaces used for map projections ?
Cylinder
Cone
Plane
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) 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
When is the grid distance greater than the ellipsoid distance?
At the very edge of the UTM zone, just past the secant point, where the scale factor is > 1
The minimum number of satellites needed for accurate ground positioning.
4 Satellites
Name the 4 error sources in GPS.
- Station Errors - Station coordinate errors or mulit-path
- Satelite Errors - orbit uncertainty and satellite clock error
- Reciever Errors - reciever clock error and reciever noise
- Observation Errors - ionospheric and tropospheric delay
What are the 3 system components of GPS?
- User Segment
- Space Segment
- Control Segment
How many hours does it take each satellite to orbit the earth?
12 hours per orbit (2 orbits per day in a 24h day).
What are the benefits of using GPS?
- 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
Why are downsides of using conventional surveys?
- 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.
Russian version of GPS.
GLONASS
What does GNSS stand for?
Global Navigation Satellite System
Chinese and European GPS Systems?
COMPASS (Chinese) and GALLILEO (European Union).
What are the 4 GNSS constellations and their country
- GPS - USA
- GLONASS - Russia
- COMPASS - China
- GALLILEO - EU
What is the orbital path and period of GPS satellites?
Mid-earth near-circular orbit
12 hour period / orbits earth twice per day
What does DOP stand for?
Dilution of precision
what are several factors that introduce error to the accuracy of GPS positioning
- 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
What reference ellipsoid is used for GPS? Which correction is applied to GPS height and why is it used?
WGS 84. The geoid height (N-value) is applied to GPS height (ellipsoid) to correct it to the elevation (H) of the topographic surface.
To determine a reasonably accurate 3 dimensional (x,y,z) coordinate point location, how many GPS satellites are required and why?
Four- one for x-position, one for y-position, one for z-position, and one to adjust for the error in the receiver clock.
List the main survey equipment components used for GPS positioning and their purpose.
- Antenna: to collect satellite signals
- Receiver: to process satellite signals
- Pole: to position precisely over poi and raise antenna to reduce signal obstruction
- Controller: to display, upload and download data
- Modem or radio: to allow for real-time communication link with reference or base stn.
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?
- 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.
What error sources does differential GPS reduce?
- satellite and receiver clock errors
- atmospheric delays
