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).
