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GIS 360: C2 (week 3-6) (Developable Surfaces & Aspect (Planar…
GIS 360: C2 (week 3-6)
Types of Coordinate systems
Geographic Coordinate System (GCS)
Based on 3D globe
Includes angular unit, prime meridian, datum
points are latitude/longitude
WGS is an example
Projected Coordinate system
assign a grid of x,y coords
built on a map projection
2D with constant lengths and angles
Types of Projections
Conformal
Preserve shape pretty well, good for topo maps. Example: Lambert conformal conic projection?
Planar (azimuthal)
Degree of angle from the North pole, large amount of distortion on the edges of these maps
To map a polar region
To map areas that have equal extent in all directions
Preserves direction
Cylindrical
Description??? Tend to be used in equatorial regions
To map tropical regions.
To map areas that extend north-south
Conic
To map mid latitudes
To map areas that extend east-west
Perspective
Position of light source relative to the globe
Gnomonic: light source at center
View the surface of Earth from the center of Earth
Stereoscopic: light source at the antipode
View one pole on Earth from the opposite pole
Orthoscopic: light source is infinitely far away
View surface of Earth from an infinite point in space
Commonly Encountered Datums
NAD 27: Uses Clarke 1866 Elipsoid,
surface based
datum (origin is in Meade Ranch, KS)
NAD 83: Earth-centered datum, most accurate in representing North America vs. the rest of the globe
WGS (World Geodetic system of 1984): Attempts to minimize global distortion. Datum that is used for GPS. Global standard for the time being. Similar to NAD83, but the Earth's mass center differs slightly between the datums.
Datum parameters
parameters of a mathematical model include: origin ellipsoid, difference between model and earth.
Developable Surfaces & Aspect
Planar Normal
Map poles
Point of tangency at one of the poles
Planar Oblique
Earth from space effect. A modified orthographic perspective
Google Earth
Planar Transverse
Tangent or secant runs along/parallel to equator.
Used for some world maps
Equatorial steriographic map
The point of contact between the globe and the planar developable surface is at the equator.
Cylindrical Normal
Used by many world maps
Aka pseudocylindirical projection
Cylindrical Oblique
useful with geographic features that are diagonally oriented
U.S. State Plane Coordinate System uses the Hotine Oblique Mercator projection
Cylindrical Transverse
seldom see a transverse mercator projection at a global extent.
local scale.
Universal Transverse Mercator (UTM) projection
Conic Normal
Lambert Conformal Conic projection
only an aspect with a tangent or secant parallel to the equator is used regularly. It is identified as the "normal" aspect
Different data used for georeferencing
Place Names: Earliest form of georeferencing, works mostly on local and city-wide scales
Postal addresses/Postal Codes: Combination of street names with postal addresses makes this an effective national georeferencing system. Hierarchically structured.
PLSS (public land survey system): Unique to the Western U.S. 36 mile square townships further subdivided into 1x1 plots. Used to map westward expansion.
Latitude and Longitude: Truly global georeferencing system. Most comprehensive and powerful form of georeferencing
To be the most effective, a georeferencing system must be: Nailed to the Earth's Surface, Globally Unique, Consistent throughout time
Cartography Requirements
Knowledge of intended audience
Identification of information to communicate
Identify area of interest
Identify physical and resource limitaitons
Digital data output
Digital data
Electronic form
Recording or converting data into a digital file format
Common format: GML = geographic markup language
Metadata
Information about spatial data
Describe the content, source, lineage, methods, developer, coordinate system, extent, structure, spatial accuracy, attributes, and responsible organization for the spatial data.
FGDC: federal geographic data committee uses CSDGM
CSDGM: content standard for digital geospatial metadata.
Identification, describing the dataset
data quality
spatial data organization
spatial reference coordinate system
entry and attribute
disturbution and option for obtaining the dataset
currency of metadata and responsible party
citation
time period information, used with other sections to provide temporal information
contact organization or person
Map Projection Cases
Simple case
1 line of tangency
Secant case
2 lines of tangency
Line of tangency
Where line cuts take place/where surface touches lines
Along these lines there is zero distortion
Also called 'standard lines'
Standard meridians
parallel to longitude lines
Standard parallels
parallel to latitude lines
Scale factors
Under tangent line (<1)
Over tangent line (>1)
On tangent line (=1)
Methods of Spatial Data Acquisition
Captured from analog maps via digitizing & scanning
Heads-up digitizing: Data captured with a mouse on the screen from an existing map. Data is produced as a vector. Positional accuracy depends on the resolution of your source.
Scanning: Uses a scanner to measure reflected light intensity. Data produced as a raster. Depending on the resolution of the scan data can "drop out".
"drop out" = encompassed within a single raster cell
Collected in the field with GPS
Collected with remote sensing
Found from existing sources
Universal Transverse Mercator (UTM)
Cylindrical projection
60 zones in the north & 60 zones in the south. Total of 120 zones
Used in US states that have a North/South orientation
Max distortion = 0.04%
Zones
Central meridian: 500,000m from false origin
false origin for each zone
secant lines are the boarder of each zone
GNSS Global Navigation Satellite System
Satellite Component
30 Active Satellites for US constellation
L1 Carrier Code
Course Acquisition Code
Need at least 4
Trilateration
Ground Control Component
Use of range pole , handheld or backpack mounted pole is easy and effective way to improve collection efficiency.
Additional information from wifi or known locations on the earth's surface improve accuracy.
Factors impacting Accuracy
Arrangement of Satellites
Atmospheric conditions
Interference from earth objects (multipath)
User Component
Handheld GNSS tablet used for field digitizing by operator in the field.
GNSS sources of error
Range calculations use the speed of light. But it is only constant in a vacuum (space). When it enters Earth it changes.
Atmospheric delays
positional error
The atmosphere is below the ionosphere. The density is significantly different from a vacuum. The variation is mostly from changing temperatures, pressure, and water vapor.
Signal velocity is slightly altered as it goes through atmosphere.
Ionospheric delays
positional error
The ionosphere surrounds the earth in a blanket of charged particles. Formed by solar radiation that strips the electrons from their elements. This changes the charges of particles and their density. This changes the electromagnetic field around the Earth.
Signal velocity is slightly altered as it goes through ionosphere.
Reducing ionospheric erros
Readjust speed value for speed of light when calculating range distance.
Use models that incorporate the charge density
Dual-free-requency receivers
Collects info on multiple GNSS signals simultaneous & uses science to remove ionospheric errors.
GPS v. GNSS
GPS (Global Positioning System) is specific to the US NAVSTAR system
GNSS is a broad term, it stands for Global Navigation Satellite System. It can be used to refer to all for systems (NAVSTAR, GLONASS, Galileo, and Chinese Compass Satellite Navigation System)
Types of GNSS
NAVSTAR GPS- United States GPS
GLONASS- Russia
Galileo- Various European governments
Chinese Compass Satellite Navigation System
Things that increase GNSS accuracy
carrier phase instead of code phase
differential correction
a range pole
range averaging of multiple position fixes
real-time correction
Remote Sensing Systems
Passive
Active
Incident Energy
spectral signiture
Remote Sensing
Passive
Collects and reflects electromagnetic radiation
Incident Energy (I) = Absorbed energy(A)+ transmitted energy(T)+Reflected energy(R)
Spectral Signatures--how you differentiate between features based on signature
Active
sends out energy signals then measures the reflected signal.
LiDAR
Advantages:
large area covered
can go beyond visible range
accurate mapping after the distortion is removed
permanent record
Resolutions
Spectral
number of wavelength regions or bands in the EM-spectrum that the sensor can measure
Temporal
How often the data are obtained of the same area of the Earths Surface
Spatial
Smallest Unit Area on ground that can be measured by the sensor, usually denoted in meters.
Dictates the amount of detail that can be determined from the data.
dependent on the field of view, altitude, and viewing angle
Raidometric
measure of the sensitivity of a sensor to differences in the intensity of the radiation measured.
finer resolution = more sensitive it is to detecting differences in the EMR intesity
8-bit sensor quantizes intensity on a scale from 0-255,
11-bit sensor quantizes intensity on a scale from 0-2047.
Spatial Data Accuracy
Positional accuracy
How close the locations of object represented in a digital data correspond to their true locations
Attribute accuracy
How different the attributes are from the true values
Logical consistency
Reflects the presence, absence, or frequency of inconsistent data
Completeness
How well the data set captures all the features it's intended to represent
Scopes of data analysis
local operations
uses data from both an input location plus nearby locations to determine the output value.
The extent and relative importance of values in the nearby region may vary.
The value at an output location is influenced by more than just the value of data found at the corresponding input location.
neighborhood operations
Uses data values from the entire input layer to determine each output value.
The value at each location depends in part on the values at all input locations.
global operations
use data at one input location to determine the value at a corresponding output location.
Attributes or values at adjacent locations are not used.
Types of Adjacency
Shared line required
Shared node required
Adjacency vs. Containment
Common Vector tools and their uses
Buffer: Creates new polygons from existing features based on proximity to other features.
Dissolve: Aggregates features that have the same value for a specified attribute
Eliminate: removes features that meet a user-defined query or expression
Overlay: Combines geometry and attributes of two different data layers to create an output.
Raster Analysis
Spatial Scope (scale of analysis
Local: Cell by cell basis
Focal: neighborhood basis
Zonal: User defined region
Global: across the whole dataset
Logical Operations (Boolean Operations)
AND
When you want two or more things to be true in a cell. select for water AND shrubs
OR
When one option or another option is good. Select for rocky beaches OR sandy beaches
NOT
Used for excluding certain values
Raster: raster extraction
Vector: clip tool
