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Select By Location
Vector Analysis
Select features from one layer based on their spatial association with another layer
Examples: Adjacency, Containment, Distance, Intersect
Adjacency
Features from one layer share a boundary with another
Containment
Features located within another feature
Distance
One feature is within a certain distance of another
Intersect
Features that fully or partially overlap another feature
Contained objects also do this
Select by attribute/location do NOT
Create a new layer
Geoprocessing
When one layer has some sort of action performed to it and a new layer is created
Layer
One file of geographic data in GIS. Can refer to either vector or raster.
Two categories of geoprocessing
One layer analysis
Two+ layer analysis
One Layer Analysis
Buffer
Dissolve
Buffer
Area of proximity that can be created around one or more objects
Can be created around points, lines, polygons
Can be used for spatial selection
features within a buffer or that intersect a buffer, etc.
Dissolve
When adjacent polygons that have the same properties have their boundaries removed
Merges polygons into a single, larger shape
Ex:
counties in a state, congressional districts, land cover types
Two+ Layer Analysis
Overlay geoprocessing operations
When two or more things that share the same spatial boundaries are combined
Union, intersect, identity, and symmetrical difference
Union
All features from both layers are combined together into a new layer. Acts as OR
Intersect
Only features that layers have in common are retained in the new layer. Acts as AND
Identity
All features of the first layer are retained
All features of the second layer where it intersects the first are also retained
Order MATTERS
Symmetrical Difference
Features of both layers are contained, except for what they have in common
Opposite of intersect
Acts as XOR
holes where they intersect
Raster Resolution
Based on cell length (one side ONLY)
Cell size = length of one side of a cell in the real world
Coarse vs fine resolution
small cell size = finer resolution
larger cell size = coarser resolution
Local Operations (Cell-By-Cell)
1 raster file
All cells have the same operation done to them using the same value
Addition, subtraction, multiplication, division, sqaure root, squaring
Zonal Operations
2 raster file
1 input, 1 zonal
Minimum, maximum, average, sum
Map Algebra
Similar to local operation
At least two rasters stacked on top of each other
Addition, subtraction, multiplication, division
GNSS
Global Navigation Satellite System
AKA GPS
Has at least 24 satellites for global coverage
NAVSTAR GPS
United States GNSS
stands for Navigation Satellite Timing and Ranging
GLONASS
Russian GNSS
Galileo
European Union GNSS
BeiDou
Chinese GNSS
Three Main Segments of GNSS
Satellite/space segment
Control segment
User segment
Satellite/Space segment of GNSS
Consists of a constellation of satellites orbiting the earth
Constellations: groups of 4 satellites in 6 orbital planes
L1
Coarse Acquisition (C/A): Code for civilian use
Precise (P): Code for military and civilian use
L2
P Code
P (Y) Code: Encrypted version of P code
Control Segment
monitoring and control stations
consist of master control stations and ground antennas
User Segment
all GPS units that receive satellite signals
What information satellites transmitt
time and location
Satellite Almanac
Contains orbit and location data for all satellites in a constellation
How to calculate distance
Distance = time x speed
Psuedorange
Distance between a satellite transmitting a signal and the receiver
3D Trilateration
Process used by satellites to find location on earth using distances
Sources of innacuracy
selective availibility
ephemeris error
position dilution of precision (PDOP)
atmospheric errors
multipath errors
Selective Availability (SA)
Intentionally introducing errors to make C/A less accurate for civilian use
Two Types
Delta Error
incorrect timing info
Epsilon Error
incorrect satellite location info (ephemeris)
Removed by US Govt in 2000
Ephemeris Error
Occurs when satellite broadcasts incorrect location information
Data is corrected and updated by a control station
Position Dilution of Precision Error (PDOP)
Error due to positional location of satellites in the sky
When satellites are too close to each other, it reduces their accuracy
Atmospheric Error
Ionosphere
Charged particles alter speed of signal, causing inaccuracies in timing
Troposphere
Water vapor delays signals
Multipath Error
Occurs when the receiver has a poor view of the sky
Objects blocking the signal (tree canopy)
Objects reflecting the signal (buildings, water)
Can’t be compensated for
Ways to improve accuracy
Differential GPS (DGPS)
Satellite-Based Augmentation Systems (SBAS)
Differential GPS
Base station at known coordinates
Base station broadcasts correction signal
GPS receivers pick up signals from 4 signals plus the correction
Example: NDGPS and CORS
Nationwide Differential GPS
NDGPS
Used by coast guard for ship navigation
Example of DGPS
Continually Operating Reference Station
CORS
Operated by National Geodetic Survey
Example of DGPS
Satellite-Based Augmentation Systems
Base stations broadcast correction to SBAS satellite
SBAS satellite broadcasts connection to GPS receiver
Example: WAAS
Wide Area Augmentation System
WAAS
Developed by Federal Aviation Administration for aircraft positional info
SBAS example
3 Categories of International Systems
Full GNSS
Regional Systems
Augmenting Systems
SBAS
Full GNSSs
NAVSTAR GPS
GLONASS
Galileo
BeiDou-2
Indian Regional Navigation Satellite System
Only regional system we’ve learned about
IRNSS
Augmented Systems
BeiDou-1
SBAS for BeiDou2
GAGAN
SBAS for IRNSS
QZSS
SBAS for Japan/Oceania
Applications of GPS
military
transportation
wildlife/livestock management
pet tracking
precision agriculture
entertainment