GIS Final Exam Review with Accurate
Solutions
geospatial data - ANSWER--has location info
-ex: symbols on a map, geotagged photo, ...
non-spatial data - ANSWER--no info about location
-ex: name, age, education level, ...
datums frequently used in the US - ANSWER-NAD27, NAD83, and WGS84
NAD27 (the North American Datum of 1927) - ANSWER--developed for measurements
of the US and North America
-US Geological Survey topographic maps originally used this
NAD83 (the North American Datum of 1983) - ANSWER--developed by the National
Geodetic Survey with Canadian agencies
-most GIS systems use this nowadays
WGS84 (the World Geodetic System of 1984) - ANSWER--developed by the US
Department of Defense
-GPS uses this for locating points worldwide in Earth's surface
the 3 projection methods that are popular - ANSWER-cylinder, cone, and plane
cylinder projection - ANSWER-cylindrical projection
cone projection - ANSWER-conic projection
RSME (root mean square error) - ANSWER--= √(SUM(x1-X1)²)/N)
-in the case of raster (image) data, maintain this as < 1/2 pixel size, so that the data
may be aligned with other data without significant displacement
-the smaller this is, the better the match is
GCPs - ANSWER--spread them
-do not use changing features such as shorelines, shadows, etc
→good ones are road intersections, dams, benchmarks, etc
-use higher accuracy datasets or higher resolution images as reference
-RSME should be < 1/2 of a pixel size in raster
, resampling - ANSWER--procedure to find pixel values from input image for output
image
-occurs during any warping of an image
-3 major methods
What are the 3 major methods of resampling? - ANSWER--w/ nominal data:
→nearest neighbor method
-w/ interval or ratio data:
→bilinear
→cubic convolution
How does GPS find your position? - ANSWER-1. pseudo-random codes are transmitted
every second
2. pseudorange is calculated
3. location is determined by trilateration
pseudo-random codes - ANSWER--C/A code (coarse acquisition code)
→broadcast on the L1 carrier frequency for civilian usage
-P code (precise code)
→broadcast on the L1 and L2 carrier frequencies for military usage
-Y code
→an encrypted version of the P code
pseudorange - ANSWER--is the calculated distance between a GPS satellite and a
GPS receiver
→as there are accuracy errors in the time measured, this term is used rather than
ranges for such distances
-= signal travel time x speed of light
-potential errors are atmospheric delays, multipath, noise, etc
how is location determined by trilateration? - ANSWER--at least 3 satellites are required
→the more, the better
What other GNSS are there beyond GPS? - ANSWER-GLONASS, Galileo, Compass,
EGNOS, and MSAS
GLONASS (Global Navigation Satellite System) - ANSWER--is the former USSR's (now
Russia's) GNSS
Galileo - ANSWER--the EU's GNSS
-currently in development
Compass - ANSWER--China's GNSS
-currently in development
Solutions
geospatial data - ANSWER--has location info
-ex: symbols on a map, geotagged photo, ...
non-spatial data - ANSWER--no info about location
-ex: name, age, education level, ...
datums frequently used in the US - ANSWER-NAD27, NAD83, and WGS84
NAD27 (the North American Datum of 1927) - ANSWER--developed for measurements
of the US and North America
-US Geological Survey topographic maps originally used this
NAD83 (the North American Datum of 1983) - ANSWER--developed by the National
Geodetic Survey with Canadian agencies
-most GIS systems use this nowadays
WGS84 (the World Geodetic System of 1984) - ANSWER--developed by the US
Department of Defense
-GPS uses this for locating points worldwide in Earth's surface
the 3 projection methods that are popular - ANSWER-cylinder, cone, and plane
cylinder projection - ANSWER-cylindrical projection
cone projection - ANSWER-conic projection
RSME (root mean square error) - ANSWER--= √(SUM(x1-X1)²)/N)
-in the case of raster (image) data, maintain this as < 1/2 pixel size, so that the data
may be aligned with other data without significant displacement
-the smaller this is, the better the match is
GCPs - ANSWER--spread them
-do not use changing features such as shorelines, shadows, etc
→good ones are road intersections, dams, benchmarks, etc
-use higher accuracy datasets or higher resolution images as reference
-RSME should be < 1/2 of a pixel size in raster
, resampling - ANSWER--procedure to find pixel values from input image for output
image
-occurs during any warping of an image
-3 major methods
What are the 3 major methods of resampling? - ANSWER--w/ nominal data:
→nearest neighbor method
-w/ interval or ratio data:
→bilinear
→cubic convolution
How does GPS find your position? - ANSWER-1. pseudo-random codes are transmitted
every second
2. pseudorange is calculated
3. location is determined by trilateration
pseudo-random codes - ANSWER--C/A code (coarse acquisition code)
→broadcast on the L1 carrier frequency for civilian usage
-P code (precise code)
→broadcast on the L1 and L2 carrier frequencies for military usage
-Y code
→an encrypted version of the P code
pseudorange - ANSWER--is the calculated distance between a GPS satellite and a
GPS receiver
→as there are accuracy errors in the time measured, this term is used rather than
ranges for such distances
-= signal travel time x speed of light
-potential errors are atmospheric delays, multipath, noise, etc
how is location determined by trilateration? - ANSWER--at least 3 satellites are required
→the more, the better
What other GNSS are there beyond GPS? - ANSWER-GLONASS, Galileo, Compass,
EGNOS, and MSAS
GLONASS (Global Navigation Satellite System) - ANSWER--is the former USSR's (now
Russia's) GNSS
Galileo - ANSWER--the EU's GNSS
-currently in development
Compass - ANSWER--China's GNSS
-currently in development
