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LSGI 521: Principles of GIS Lecture 3: Data AcquisitionLSGI 521: Principles of GIS Lecture 3: Data Acquisition
LSGI 521: Principles of GIS
Lecture 3: Spatial Data Acquisition in GIS
Dr. Bo Wu [email protected]
Department of Land Surveying & Geo-InformaticsThe Hong Kong Polytechnic University
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
1. Learning outcomes2. Data acquisition: Manual digitization 3. Data acquisition: Field survey4. Data acquisition: Remote sensing and
photogrammetry
Contents
photogrammetry5. Data acquisition: LiDAR6. Data acquisition: GPS and other
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• By the end of this lecture you should be able to:– Describe how paper maps are digitized– Know the basic ideas about remotely sensing– Know the basic image process methods– Explain what is and how to process LiDAR data into
Learning Outcomes
GIS– Know what is GPS and its integration with GIS
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Data Input Stream in GIS
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Digitizer – the equipment for digitizing• Operational procedure of digitization• Coordinate transformation• Error in digitization
Data Capture by Manual Digitization
g• Editing operation in digitization • Factors affecting digitization accuracy
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Digitizing Table • Mouse • Paper map
Elements of a Digitizer
A small size digitizer
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A large size digitizer
Mouse with buttons and cross-hair
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
1. Mount the map sheet on the digitizing table surface flat and secure
2. Identify points with known coordinates.– Tic marks or control points– Minimum two points depending on the software
P i t h ld b ll di t ib t d d d th ti t
Operational Procedure of Manual Digitization
– Points should be well distributed and covered the entire area to be digitized (usually, four corners of the map sheet)
3. Digitize control points and enter the true coordinatesinto the system
4. Software will compute coordinate transformationparameters and the residual– If residual is larger than the specified tolerance, you are
required to redo the entire procedure.
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
5. Digitize Check Point– Check point is necessary to ensure that the map sheet
mounted on the surface has not been changed or drafted.
Operational Procedure of Manual Digitization (cont’d)
6. Digitizationo Two modes : point and
stream (time or distance)
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o Points digitized will be transformed from the digitizer local coordinates system to the known coordinates system using the computed transformation parameters
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Map Digitization
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Digital map captured from digitizationMap before digitization
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Coordinate Transformation Models
• Affine Transformation– Parallelity is still maintained, however the azimuth can be changed
y
x
• Similarity Transformation– Parallelity & azimuth of lines are maintained– 4 parameters
X' = a1x + a2y + a3
Y' = -a2x + a1y + a4
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• Projective Transformation– Parallelity and azimuth are not maintained– 8 parameters
X' =
Y' = 1 +y a + xaa +y a + xa
54
876
1 +y a + xaa +y a + xa
54
321
y
x
y
x
– 6 parameterX' = a1x + a2y + a3
Y' = a4x + a5y + a6
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Overshoots• Undershoots• Omitted edges or nodes• Duplicated edges or nodes• Mislocated edges or nodes
Errors in Manual Digitization
Duplicate edges
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+
+
+
+
Omitted edge
Duplicate Label
Overshooting
Duplicate edges
Undershooting
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Possible Errors in Digital Map
Geometric Errors– A node is missing or
misplaced.– An edge is missing or
misplaced.
Topological Errors– Unconnected edges exist.– A polygon has a gap
between two edges, that is it is not closed.
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p– An edge has a bad shape
or too many (too few) points.
– A node has more than one position.
– Duplicate arcs are present.– A polygon has more than
one or no reference point associated with it (label point).
– A polygon may be missing.
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Factors Affect the Accuracy of Manual Digitization
1. Quality of original documente.g. drafting method, drafting media,
draftsman skill
2. Proper procedure of digitization and softwaree.g. digitization of control points,
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accuracy of control points,
digitization modes
3. Quality and resolution of the digitizere.g. resolution, repeatability, selectivity,
consistency
4. Operator's skill and concentration
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Field Survey
• SurveyingHorizontal
– Traverse– Triangulation– Trilateration
Vertical
β
North
α
– Leveling
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A
B
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Survey Instruments
Level and Staff
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Reflector Total StationElectronic Theodolite
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• The collection of data without being in contact with the object.• There are usually two kinds of data we want to collect: thematic and
positional.• Thematic data tells us what the object is while positional data tells
us where the object is located.
Remote Sensing
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Energy Source & Spectral Bands
• Visible Bands– Blue (0.45-0.52 μm)– Green (0.52-0.60 μm)– Red (0.63-0.69 μm) – Panchromatic (0.50-0.90 μm)
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Spatial Resolution
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Ground sample distance (GSD) : The ground distance represented by the width of a pixel
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Landsat TM (1982): 30 m• SPOT-5 (2002) : 5 m• IKONOS (1999):
– Panchromatic : 1 m– Multispectral : 4 m
• QuickBird (2001):
Spatial Resolution of Typical Sensors
China’s first survey satellite willQuickBird (2001):– Panchromatic : 0.61 m– Multispectral : 2.4 m
• GeoEye (2008): – Panchromatic : 0.41 m– Multispectral : 1.65 m
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China s first survey satellite will be launched in 2011 with the resolution of 2.5 m and 4 mChina’s Chang’E-1 CCD Camera (2007): 120 mNASA’s Lunar Reconnaissance Orbiter Camera (2009): 0.5 mNASA’s Mars Reconnaissance Orbiter Camera (2006): 0.3 m
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Spectral Resolution
The narrower the wavelength bands the sensor can detect, the higher the sensor’s spectral resolution
• Panchromatic sensors– To record the overall brightness of a scene– A camera with black and white film
• Multispectral sensorsp– Simultaneously record multiple wavelength bands– Landsat Thematic Mapper: seven multispectral bands– IKONOS and QuickBird: four multispectral bands
• Hyperspectral– Simultaneously record data in hundreds of contiguous, very narrow
spectral bands in UV, visible, NIR, mid-IR bands– EO-1: 254 bands, 10 nm resolution
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Panchromatic Image
Tampa Bay, FL
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Multispectral Images
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Multispectral Image Analysis
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Hyperspectral Imagery
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Band 1, 399 nm Band 100, 1310 nm Band 206, 2466 nm
… … … …
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Airborne
– Aerial photographs
– SAR, InSAR
• Satellite
Remote Sensing Platform
• Satellite
– Landsat, SPOT, IKONOS, QuickBird
• Ship/boat
– Sonar
– Underwater Video
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Airborne Remote Sensing
The first form of remote sensingEquipment :
• Cameras, • Photographic films, and • Camera filters.
Nevertheless recently high electronic system, the aerial photograph will ti t b i f f t i
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continue to be primary form of remote sensing.
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Use Fixed-wing aircraft• Flying over the area in the zigzag pattern• Flight attitude : 3,000~4,000m• Scale : 1:20,000~1:24,000• Sidelap : 30%• Overlap : 60%
Airborne Remote Sensing
Overlap : 60%
All ground feature will appear on at least two photo.
31Pushbroom CCD Camera
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Stereo Image Processing & 3D Reconstruction
S1
a2
a1
A
B
b2
b1
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S2
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Aerial Photogrammetry
g61 g62
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Interior Orientation• Exterior Orientation• Aerial Triangulation• Collinearity Equations
)()()( ZZRYYRXXR −+−+−
Aerial Photograph Geometry
)()()()()()()()()()()()(
333231
2322210
333231
1312110
sss
sss
sss
sss
ZZRYYRXXRZZRYYRXXRfyyy
ZZRYYRXXRZZRYYRXXRfxxx
−+−+−−+−+−
−=Δ−−
−+−+−−+−+−
−=Δ−−
⎥⎥⎥
⎦
⎤
⎢⎢⎢
⎣
⎡
−++−−+−+
=ϕωϕωϕ
κωκϕωκωκϕωκϕκωκϕωκωκϕωκϕ
coscoscossinsincossinsinsincoscoscossinsinsinsincossinsincossincossincoscossinsincoscos
R
))((2))(2())((
))((2))(2())((
0012
02
24
22
10
0022
02
14
22
10
yyxxpyyrprkrkyyy
yyxxpxxrprkrkxxx
−−+−+++−=Δ
−−+−+++−=Δ
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Most satellite sensors detect electromagnetic radiation (EMR) electronically as a continuous stream of digital data. The data are transmitted to ground reception stations, processed to create defined data products, and made available for sale to users on a variety of digital data media.
Satellite Remote Sensing
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Application of Satellite Images
Deforestation in Bolivia
1975 1992 2000
1973
Mississippi Delta sediment deposition
1989 20039/14/2011 36
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
High-Resolution Satellite Imagery
IKONOS Image 1 m Resolution
QuickBird Image0.6 m Resolution
Mars HiRISE Image
0.3 m Resolution
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Satellite Image Geometry
Rational Function Model
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Image interpretation – The detection, identification, and measurement of specific
features
• Digital image classification– Classification of the total scene content into a limited
number of major classes
Deriving Information from Remote Sensing Images
number of major classes
• Data transformations– Mathematical operations on satellite image spectral data
that enhance the interpretation or discrimination of selected terrain features
• Change detection– Detection of numerical differences in corresponding pixel
values between dates 9/14/2011 39
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• LiDAR• RADAR• SAR• SONAR
Other Remote Sensing Technologies
Questions:Do you know about any of these technologies?
What are these abbreviations stand for? Difference among them?
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Data Capture by Laser Scanning
• Terrestrial scanning
• Airborne scanning
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
LiDAR
• LiDAR = Light Detection and Ranging• Pulse of LASER light emitted• Return time and intensity measured• Converted into 3D coordinates
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
LiDAR Data Format (LAS)
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ALS Points Projected on the Orthophoto
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Cyber City Modelling from LiDAR Data
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Scanned Urban Area
3D Cyber City Model
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Object Detection from LiDAR Data
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3D visualisation of the LiDAR points Photo taken from the site
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
RADAR and SAR
RADAR = Radio Detection and Ranging A RADAR system has a transmitter that emits either microwaves or radio waves that are reflected by the target and detected by a receiver. Although the signal returned is usually very weak, the signal can be amplified. This enables RADAR to detect objects at
h h i i h
SAR = Synthetic Aperture Radar SAR is a form of radar in which the large, highly-directional rotating antenna used by conventional radar is replaced with many low-directivity small stationary antennas scattered over some area near or around the target area. The many echo
f i d h diff
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ranges where other emissions, such as sound or visible light, would be too weak to detect.
waveforms received at the different antenna positions are post-processed to resolve the target.
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• SONAR = Sound Navigation And Ranging• Sound waves travel in water at about 1,500
m/sec.• Types
– Side-scan sonar
SONAR
Side scan sonar– Single-beam sonar– Multi-beam sonar
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Global Positioning System (GPS) – American version of satellite positioning system– Initiated in 1973– 24 satellites.
• Global Navigation Satellite System (GLONASS)– The Russian version of satellite positioning system– Initiated in 1982
Global Positioning System (GPS)
– 17 satellites
• Galileo Positioning System– Europe version of satellite positioning system– Initiated in 2005– Expect 30 satellites (1 on orbit now)
• BeiDou Positioning System– Chinese version of satellite positioning system– Initiated in 2000– Expect 35 satellites (4 on orbit now)
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
GPS Instruments
About US$300 in 1999
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About US$3,000 in 1999
LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Mathematically, we need four satellite ranges to determine exact position.
How GPS Works
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Position Measurement
1 2
53
3 • The forth measurement from the forth satellite is necessary to determine the final position of the object
• But usually three ranges are enough because one of the two points is a ridiculous answer (either too far from Earth or moving at an impossible velocity) and can be rejected without a measurement
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
Use GPS for Positioning
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Remote Sensing Tutorial: http://rst.gsfc.nasa.gov/Front/tofc.html
• Aerial Photography and Remote Sensing: http://www.utexas.edu/depts/grg/gcraft/notes/remote/remote.html
Further Readings
• Digital Image Processing: http://www.cla.sc.edu/geog/rslab/rsccnew/
• Earth Science Pictures: http://pao.gsfc.nasa.gov/gsfc/earth/pictures/earthpic.htm
• GPS (highly recommended): http://www.trimble.com/gps/index.htm
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LSGI 521: Principles of GIS Lecture 3: Data Acquisition
• Summarization of the main ideas presented in this lecture:
Review
• Questions?
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