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GIS I > Lecture 6 (GIS Data Collection) > Flashcards

Lecture 6 (GIS Data Collection) Flashcards

1
Q

Data Collection

A

Adding geographic data into a GIS database.
- One of most expensive and time consuming GIS activities
-Many diverse sources
- Two broad types of collection
-> Data capture
– Two broad capture techniques (direct entry)
• Primary (direct measurement)
• Secondary (indirect derivation)
-> Data transfer
– importing the existing data from other sources into a GIS database
DATA MAINTENANCE IS MORE IMPORTANT AND COMPLEX THAN DATA COLLECTION

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2
Q

Data Collection Techniques

A
  • Primary data sources are captured specifically by direct measurement.
  • Secondary sources are reused or obtained from other systems.
    SEE SLIDE
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3
Q

Primary Data Sources

A

Digital and analog format
Raster - Digital remote sensing images/ digital aerial photographs
Vector - GPS measurements/ Survey measurements

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4
Q

Secondary

A

Digital and analog format
Raster - scanned maps/ photographs/ DEMs from maps
Vector - USGS Topographic maps/ Toponymy (place-name) data sets from atlases

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5
Q

Primary way

A

Measure terrain directly/ Digital imagery collected with LiDar

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6
Q

Data Collection - Digitalizing

A
  • Analog data must be digitized before adding to a GIS database.
  • Analog-to-digital transformation
  • > Scanning paper maps or photographs
  • > Optical character recognition (OCR)
  • > Text describing geographic object properties
  • > Vectorization of selected features

SEE SLIDE

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7
Q

Data Collection Project Workflow

A

1) Planning (establish users’ requirements, gathering all resources), 2) Preparation (obtain existing data, hardware/ software), 3) Digitizing/ Transfer (Require most efforts, Survey data entry, scanning, photogrammetry), 4) Editing/ Improvement (Validate data, Correct errors, improve quality), 5) Evaluation (Identify if the project succeeded, or failed)

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8
Q

Primary Data Collection

A 
Raster
- Remote Sensing (Aerial Photography, Satellite Imagery)
Vector 
- Ground Survey
- GPS (Global Positioning System)
- LiDAR (Light Detection and Ranging)
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9
Q

Raster Primary Data Capture

A
  • Remote sensing – the most popular form
    -> The measurement of physical, chemical, and
    biological properties of the objects without direct
    contact.
    -> Information derived from the measurement of the amount of electromagnetic radiation reflected,
    emitted, or scattered from objects.
    -> Passive sensors (limitation: cloud effect)
    • Rely on reflected solar radiation or emitted terrestrial radiation (by sun light)
    -> Active sensors – synthetic aperture radar (SAR)
    • Generate their own source of electromagnetic radiation
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10
Q

Raster Primary Data Capture

A 
Remote Sensing 
- Satellite imagery
-> Earth-orbiting satellites 
– collect information from parts of Earth surface at regular time intervals.
- Aerial photography
-> Fixed-wing aircraft
-> Smaller area in great detail
-> Suitable for detailed surveying and mapping projects
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11
Q

Raster Primary Data Capture - Remote Sensing (Four Key Aspects of Resolution)

A
  • Spatial resolution – pixel size: The size of object to be resolved
  • Spectral resolution
  • > The parts of electromagnetic spectrum to be measured
  • > Different objects emit and reflect different types and amounts of radiation (e.g., Landsat 8, 0.435 nm ~ 2.297 nm; 11 bands)
  • > Single band (value range: 8 bit [0-255]) or multiband/multispectral
  • Radiometric resolution- How finely the radiometric resolution a system can represent or distinguish differences of intensity, and is usually expressed as a number of bits (8 bit [0-255]).
  • Temporal resolution – repeat cycle
  • > Describe the frequency of images to be collected for the same area

ALL SENSORS NEED TO TRADE OFF BETWEEN THESE RESOLUTIONS, B/C OF STORAGE PROCESSING AND BANDWIDTH CONSIDERATION

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12
Q

GeoEye 1 (2008) and 2 (not currently scheduled to launch)

A

Geoeye2 : .34m spatial, spectral, radiometric, temporal
4 multispectral bands
SEE SLIDE

The resolution of the satellite image is 0.41 meter in panchromatic image and 1.65 m in multispectral imagery (Repeat cycle is between 2.1-8.3 days).

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13
Q

Worldview 2 - Satellite

A

8 multispectral bands 2.0m
Panchromatic (B&W): .5m
The resolution of the satellite image is .5 m

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14
Q

Vector Primary Data Capture

A
  • Ground Survey - Shifting from measurement-based to coordinate-based
  • GPS (Global Positioning System) - Receiving the orbit satellite signals to calculate the location through trilateral
  • LiDAR - Light Detection and Ranging - Using scanned laser range-finder to produce accurate topographic surveys with great detail.
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15
Q

Vector Primary Data Capture

A

Surveying

  • > Principle: 3D locations of objects determined by angle and distance measurements from known locations (benchmark point)
  • > All points obtained from survey measurements, and their locations are relative to other points.
  • > Time-consuming and expensive activity
  • > Uses expensive field equipments and crews
  • > Most accurate method for large scale, small areas
  • > Provide the georeference points for other fine-scale images

Ex. Leica Total Station

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16
Q

Vector Primary Data Capture

A

GPS – Global Positioning System

  • > Consist of a system of 24 satellites, orbiting the Earth every 12 hrs, at the elevation of 20,200km
  • -> Transmitting radio pulses at precisely timed-interval
  • > Four satellites to locate a three dimension (x,y,z)
  • > Differential GPS (DGPS) used to improve accuracy
  • —–> Combines GPS signals from satellite with correction signals via radio/telephone from base station
Pen Portable PC and GPS - Originally funded by the US Dept. of Defense
• Navigation
• Mapping
• Surveying
• Other applications 
needed precise positions
EX. Kinematic GPS Surveying
17
Q

Vector Primary Data Capture

A

LiDAR (Light Detection And Ranging)
-> Active sensor
-> Using lasers to measure distances to reflective surfaces
-> Point cloud: a massive collection of independent points (x, y, z)
-> Collect extremely large quantities of very detailed information
• 200,000 points per second
• Accuracy around 10 cm

Ex. Multiple Pulses in Air (MPiA) doubles pulse rate
Alliance for Integrated Spatial Technologies (SLIDES)

18
Q

Secondary Geographic Data Capture

A 
- Data collected from other purposes can 
be converted for use in GIS projects
- Raster conversion
-> Scanning
- Vector conversion
-> Digitizing/Vectorization
-> Photogrammetry
-> COGO – coordinate geometry
19
Q

Raster Conversion

A

-> Scanning – convert hard-copy analog media into digital images by scanners
• Scanner – scan the line across the map to record the amount of light reflected from data sources
-> Sources:
• Maps, Aerial photographs, Documents, etc

20
Q

Digitizing/ Vectorization

A

-> Process of converting raster data into vector data
-> Collection of vector objects from maps, photographs, image, etc.
• Primary sources
• Secondary raster data

21
Q

Georeference/ Georegistration

A

-> Convert image coordinates into database coordinates by geometric transformation process/algorithms
• Photo image
• Coordinate database
• Three reference/control points

22
Q

Image Rectification Using Ground Control Points (GCPs)

A
  1. Identify GCPs on image and reference
  2. Develop transformation equations
  3. Resample to determine digital number (DNs) for
    corrected image pixels
    1st Order Polynomial
    2nd Order Polynomial

See SLIDE

23
Q

Resampling

A
  • Used to determine the pixel DN values to fill in the output matrix by sampling from original (distorted) image
  • Nearest Neighbor
    -> Uses closest pixel value
    -> Discreet data
    • Classes, land use
  • Bilinear Interpolation
    -> Uses 4 closest neighbors
    -> Continuous data, localized
    • Elevation data
  • Cubic Convolution
    -> Uses 16 closest neighbors
    -> Continuous data, smoothest (IMAGES)

SEE SLIDEs (EXAMPLES)

24
Q

Vector Secondary Data Capture - Digitizing/ Vectorization

A

Manual digitizing – vertices defining point, line, polygon

  • > Point – screen cursor to record the location by clicking button
  • > Stream-mode – partially automated collecting vertices ( .25 sec, .02in)

EX. Heads-Up Digitizing and Vectorization

25
Q

Photogrammetry

A

-> the science and technology of capturing measurements from images
-> 2D measurement – point, line, area
-> 2.5D or 3D measurement – height, elevation
• Stereopair of photographs
– 60% overlap along each flight line
– 30% overlap between flight lines
-> View stereo/3D model
• Split screen with stereoscope
• Special glasses to observe
red/green display or polarized light

SEE SLide (Ex. Stereo Pair, 2.5D v 3D)

26
Q

Coordinate Geography (COGO)

A
  • Capturing and representing geographic data
  • Same principles as the survey
  • > Bearings, distances, and angles to define each part of an object
  • The only legally acceptable definition of land records and property parcels in U.S.
  • > Very precise measurements
  • > Highly qualified individual objects

COGO stands for coordinate geometry, it is
a vector data structure and method of data entry.

SEE SLIDEs

27
Q

Data Transfer

A
  • Buy vs. build is an important question
  • Many widely distributed sources of GI
  • Finding existing map data
    -> Map library – network search, or media such as CD-ROM and disk
    -> Internet search – World Wide Web
    -> Federal, state, and local agencies (Geospatial one-stop, NSDI - Data clearinghouse, USGS - National Map, EROS, NOAA, Census Bureau, EPA, USDA)
    -> GIS vendors package data with commercial
    products (geocommunity, geoplace)

Portland Metro’s Regional Land Information System (RLIS)

GIS I (7 decks)

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