Unit 6: Spatial data collection methods

Geocoding problems and solutions

Problems: -New or irregular street addresses -> new subdivisions and rural roads, non-grid street systems, international countries -expensive street reference data (international streets are very expensive data) Solutions -Instead of street, match by zipcode or city centroid: low accuracy -Parcel matching: parcel data required -Geocode with GPS (latitude and long. info): locations were recorded with GPS have highest accuracy

Digitizing

-Captures map by tracing lines by hand -Heads-up digitizing: done directly on a computer monitor -Tablet digitizing: uses a cursor and an electronically sensitive tablet -Results are a string of points with (x,y) values -> basically tracking, so making vector based lines -Only works for paper maps

Important GPS contacts

-Coast Guard -FAA -GPS.gov

GPS: Global Positioning System

-Constellation of at least 24 satellites that provides worldwide accuracy position coordinates -Uses satellites and coordinates to determine position on Earth -US Department of Defense is in charge of it -Free of charge

Satellite Imagery

-Corona satellite program -Space-borne imaging -Current satellite imagery has very high resolution -2-4 inches resolution -commercially available photographs -satellites can "read license plates" from space, but it is not practical and often difficult -different satellite programs offer different advantages -> spectral vs. spatial resolution -Landsat program most often incorporated

More on Remote sensing

-Feature extraction: based on mutli spectrum band values, software will create (extract) certain features (derived data) -classifications: based on multi spectrum band values, software will assign classes to the values

GPS Data Collection

-GPS records various types of info -location, elevation, speed, attributes, create virtual maps -Much is dependent on the devise used to collect info -handheld GPS (3-150m, satellite only), vehicle GPS, cellphone, station (engineering) GPS (1mm-30m, satellite and/or base station antenna), assisted GPS devices (3-150m, satellite, cellphone towers, wifi, and other Earth-based antenna) -ACCURACY COMES FROM SPEED OF RECEIVER/HOW OFTEN YOU ARE PINGED

Aerial Photography Interpretation

-Interpretation is an art of identifying and judging spatial objects by carefully examining photographs -Tone: relative brightness or color of elements on a photograph -Size: objects must be considered in the context of the scale of a photograph -Shape: the general outline of objects ->regular geometry probably means human activity -Texture: impression of smoothness or roughness by frequency of change of tone -pattern or spatial arrangement: consider difference between naturally occurring and man-made -Shadow: determines the height of objects in aerial photographs can can obscure objects -Site: topographic and geographic location -Association: some objects are always found in association with other objects. Context can provide insight

GIS data creation and conversion

-It costs a lot to create data in terms of both time and money -If data is reused, there could be just one time cost, but it does require maintenance -Eliminate cost: find existing data

Remote sensing applications

-Land cover/use mapping and detection -natural disaster and risk mapping -global warming and climate change -biodiversity -landscape measurement/prediction -environmental health related problems

Remote Sensing: photography

-different wavelengths of light reflected from the object onto the film produce the image -different chemical reactions form different colors -different chemical sensitivity or layers produce black and white, color, or near infrared -camera settings produce all kinds of outputs

RADAR Imaging

-Radio detection and ranging -uses radio waves -uses active microwaves -used to detect, range (distance), and map objects -adapted for mapping topography of land masses and bathymetry

Data input methods for spatial data

-Scanning -Digitizing -Build maps from field data collection -GPS, survey data, address data, aerial photos, satellite imagery

Remote sensing

-Science of obtaining info through analysis of data acquired by a device at a distance -> collecting data while not there in person -Usually aerial photography or satellite data -sensors collect data from a portion of the electromagnetic spectrum at a given resolution (pixel size) -> raster -electromagnetic spectrum (energy radiation) -different matter has different reflectance values in the electromagnetic spectrum, so depending on what you're using, you seen different colors

Digitizing Process

-Stable base map -fix to tablet -digitize control -determine coordinate transformation -trace features -edit -clean and build

Image Band

-each band can detect certain features better than others 1. Coastal water mapping 2. Vegetation 3. plant species 4. Soil moisture monitoring 5. Vegetation moisture 6. Surface temperature 7. Mineral and rock discrimination

Reference (look-up table) Data Sources

-Traditional geocoding services require reference (geocodable streets) data -Source options: Census TIGER/Lines, Google, TeleAtlas, Here

Satellite imagery advantages

-efficient: helpful in finding stuff not visible to human eye without conducting extensive field research -versatile-can be used in various disciplines

How does geo coding work?

-You have original address, which is parsed (city, state, zipcode, etc) -Street database (reference file) looks for best matching records 1. Rooftop geocoding -> google maps 2. Proportional geocoding: takes line segments and proportions out

Landsat 7

-can collect 7 images at once -each image shows a specific section of the electromagnetic spectrum or band

GPS Segments

-control: In Colorado, with some monitor stations and ground antennas -Space (satellites): 24 satellites that orbit earth twice a day while sending coded radio signals -orbits are arranged so that there are at least 4 satellites visible anywhere -User: GPS receivers to collect and process signals from GPS satellites that are in view

Georeferenceing

-conversion of spatial information to digital form -capturing the map and the attributes of locations -georeferencing leaves a stamp on the data -> method of georeferencing can influence structures, errors, and analysis associated with spatial info -ex. scanning (raster), digitizing (vector)

Satellite imagery disadvantages

-could be expensive, if you need good quality (no cloud) -learning curve: you need good software and deep understanding of imagery and analysis

Supervised

-create a training file by identifying sample groups/classes -create a signature file using your knowledge and image bands -evaluate the signature file -classify -Interpret -THE DIFFERENCE IS YOU GROUP THESE YOURSELF

Unsupervised

-create signature file by identifying classes (clusters) using statistics -evaluate signature file -classify -Interpret

Street Address geocoding

-formats differ around the world -GIS does not interpret street address directly -GIS needs a database "lookup table" to match address -Can be difficult cleaning data and knowing what system you're using -many different softwares and methods, and how good of a match you'll get depends on the geocoder used

Similar Location Data Collection

-location identified by cellphone towers and wifi spots -Usage: -authorities to combat crimes -Navizon: commercial application -OpenCellID: tells you where all the cell towers are -Find my mac/iphone: gets approximate location using database of wifi hotspots

Orthophorography

-normal photograph cannot be used for mapping because of camera tilting and topography causing distortion -> no uniform scale, impossible to make measurement -photo must be rectified and transformed into an orthophoto -An orthophoto is a uniform scale

Basic processing

-original images are in black and white -to be able to see the differences with human eyes, images will be typically composed (stacked up) and shown using three primary colors on the computer screen

Scanning

-pass map through beam, which measures reflected light intensity -Result is a grid of pixels ->image size and resolution are important (raster data) -Allows for heads up digitizing -Types of scanners: flat bed, drum, roll-top -Resolution affects processing efficiency of the computer -Lower the DPI, smaller the file, but also less detail that is captured -Only works for paper maps

Stereo photography

-photos are taken of the same area with about 30-50% overlap -occurs because of parallax -> allows for depth of judgment -3D photography

Geocoding variations: Reverse geocoding

-pick closest street address by clicking on a map 1. I cannot geocode a location because there are no streets nearby, but I want to know where it is 2. I know geographic coordinates but I want to know a street address for this location (or city or zipcode)

Aerial photography

-pictures taken from high up in the air -low-altitude aircraft can produce images down to sub-centimeter resolution

Common digitizing errors

-slivers -duplicate lines and nodes -unended lines -gaps

Geocoding

-the process of assigning a pair of APPROXIMATE geographic coordinates to each case (with spatial information such as address_ -2 elements: source and reference files Address matching: most common geocoding method, matching street addresses with reference street data -address matching methods vary by country

Geocoding web services

-use of predefined online geocoding services in ArcGIS -Advantage: no reference is necessary -Disadvantage: limited geocodable cases in general, and not much control over the results

Civil Engineering Survey

-uses a theodolite or survey transit -records distance and elevation from a known location with a stadia rod -trigonometry and geometry determine the size and shape of a landscape -Accuracy varies from manual equipment to laser guided automation

LIDAR imaging

-uses pulsated laser light to measure travel time from the laser transmitter to a target and back to determine ground surface elevation with high vertical accuracy, available as 2-D image

Geocoding variations

-zipcode/city matching -can match data with zipcode points or polygons -2 elements: -Source file -reference file

Geocoding Process in ArcGIS

1. Build a geocoding service (aka geocoder, locator): define a method, reference data & fields, (quality) thresholds/criteria, and output data 2. Run the service against your table data 3. Manual intervention/corrections: manually match unmatched cases that didn't satisfy the defined service thresholds/criteria 4. Try lower quality geocoding service to achieve a higher geocoding rate -> geocode based on second best spacial info, ex use zipcode instead of street address

How does GPS work?

1. Control segment constantly monitors GPS constellation and uploads info to satellite 2. GPS receiver collects radio signals from GPS satellites in view 3. GPS receiver accounts for errors 4. GPS receiver calculates distance to each satellite to determine the current location (position triangulation), and then displays info on the screen -> so need at least 3 satellites to get location and elevation -No access to direct sky means weak signal, tho some supplemental systems help improve accuracy -Some supplemental systems are WAAS (Western hemisphere) and Post-processing, which corrects GPS data by matching ground station data -Base antenna from known locations act as satellites on Earth

GPS error management (6)

1. Selective availability: US gov can turn off satellites or move them 2. Visible satellites: buildings, terrain, electronic interference, etc can cause positioning errors or not get position reading at all due to blocked signals -> can't see sky, can't get signal 3. Signal multipath: GPS signal is reflected off objects, which increases travel time of signal, causing errors 4. Receiver clock errors: built in clock is not as accurate as the atomic clock on satellites 5. Orbital errors: inaccuracy of satellite's reported location -> satellite could be moved 6. Atmospheric delays: GPS system uses built-in model that calculates average amount of delay to partially correct for this 7. Satellite geometry/shading: relative position of satellites at any given time-> ideal geometry exists when satellites are located at wide angles relative to each other (ex. want satellites to be further apart, but there might be a building in the way)

Classification Methods (2)

1. Supervised 2. Unsupervised