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WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
WFM 6202: Remote Sensing and GIS in Water
Management
[Part-B: Geographic Information System (GIS)]
Lecture-3: Input of Geospatial Data
Akm Saiful Islam
Institute of Water and Flood Management (IWFM)
Bangladesh University of Engineering and Technology (BUET)
December, 2006
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Data Acquisition
As data acquisition or data input of geospatial data in
digital format is most expensive (about 80% of the total
GIS project cost) and procedures are time consuming in
GIS, the data sources for data acquisitions should be
carefully selected for specific purposes.
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Required Data Sources for GIS
•
Analog maps
Topographic maps with contours and other terrain features and
thematic maps with respect to defined object classes are digitized by
digitizers manually or by scanners semi-automatically.
•
Aerial photographs
Analytical or digital photogrammetry is rather expensive but the best
method for updating
•
Satellite image
Satellite images or data are available for land use classification, digital
elevation model (DEM), updating highway network etc.
•
Ground survey with GPS
Total station together with GPS (Global Positioning System) will
modernize the ground survey.
•
Reports and publications
Social economic data are usually listed in the reports of statistics and
census with respect to administration units.
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Compare data acquisition methods
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Digitizers for Vector Data Input
The digitizing operation
 Step 1 : affixed a map to a digitizing table.
 Step 2 : add control points or tics at four corners.
 Step 3 : digitize map contents according to the map layers
 Step 4 : editing errors and clean the dataset Step 5 : convert from
digitizer coordinates to map coordinates to store in a spatial database.
Tablet digitizers with a free
cursor connected with a
personal computer are the
most common device for
digitizing spatial features with
the planimetric coordinates
from analog maps.
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Major problems of map
digitization
• The map will stretch
or shrink day by day
which makes the
newly digitized points
slightly off from the
previous points.
• The map itself has
errors.
• Discrepancies across
neighboring map
sheets will produce
disconnectivity.
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Selecting a digitizing technique
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Scanners for Raster Data Input
• Scanner are used to convert from analog maps or photographs
to digital image data in raster format.
• Mechanical Scanner
It is called drum scanner since a map or an image placed on a
drum is digitized mechanically with rotation of the drum and shift
of the sensor. It is accurate but slow.
• Video Camera
Video camera with CRT (cathode ray tube) is often used to
digitize a small part of map of firm. This is not very accurate but
cheap.
• CCD Camera
Area CCD camera (called digital still camera) instead of video
camera will be also convenient to acquire digital image data. It is
more stable and accurate than video camera.
• CCD Scanner
Flat bed type or roll feed type scanner with linear CCD (charge
coupled device) is now commonly used to digitize analog maps
in raster format, either in mono-tone or color mode. It is accurate
but expensive.
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Major Types of Scanner
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Performance of major scanners
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
I/O of scanning process
(a) original document
in black (with scanner
resolution in green)
(b) scanned document in
gray scale pixel (0=black,
255= white)
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Digital Mapping by Aerial
Photogrammetry
• Analytical Photogrammetry
Though computer systems are used for aerial
triangulation, measuring map data, editing and output
with pen plotter, a stereo pair of analog films are set up
in a stereo plotter and the operator will manually read
terrain features through stereo photogrammetric plotter
called analytical plotter.
• Digital Photogrammetry
In digital photogrammetry, aerial films are converted into
digital image data with high resolution (5-25mm). Digital
elevation model (DEM) is automatically generated with
stereo matching using digital photogrammetric
workstation.
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Procedures
of
Aerial
Phtogrammetry
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Remote Sensing with Satellite
Imagery
• Satellite remote sensing is a modern technology to
obtain digital image data of the terrain surface in the
electro-magnetic region of visible, infrared and
microwave.
• Multi-spectral bands including visible, near-infrared
and/or thermal infrared are most commonly used for
production of land use map, soil map, geological map,
agricultureal map, forest map etc. at the scale of
1:50,000 ~ 250,000.
• A lot of earth observation satellites for example landsat,
SPOT, ERS-1, JERS-1, IRS, Radarsat etc. are available.
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Earth Observation Satellites
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
High Resolution Satellites
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Advanced Technologies for Primary
Data Acquisition
Following advanced technologies will be useful for future GIS.
•
Electronic Plane Surveying System
An integrated system of total station with automated tracking function,
kinematics global positioning system (GPS) and a pen computer will replace
the conventional plane surveying.
•
Mobile Mapping System
Different sensors such as GPS, INS (inertia navigation system), more than
two digital cameras, voice recorder etc. are fixed on a vehicle in order to map
objects in close range.
•
Laser Scanner
Airborne laser scanner together with GPS and INS will measure directly the
terrain releif or DEM with the height accuracy of 10 cm up to the altitude of
1,000 m.
•
SAR Interferometer
SAR (synthetic apperture radar) inter-ferometry is a new technology to
produce DEM automatically by special interferometric processing of a pair of
SAR images.
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Advanced Technologies
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Advanced Technologies (contd..)
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Rasterization
• Conversion between raster and vector data is very
useful in practical applications of GIS.
• Rasterization refers to conversion from vector to
raster data.
• Raster format is more convennient to produce color
coded polygon maps such as color coded land use
map, while map digitizing in vector format is more
easier to trace only the boundary.
• Rasterization is also useful to integrate GIS with
remote sensing becaues remote sensing images are
in raster format.
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Conversion Vector to Raster
• trapezoid area can be applied to convert vectorized
polygon to rasterized polygon with grid cells
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Vectorization
• Vectorization refers to conversion from
raster to vector data, which is often called
raster vector conversion.
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Raster Vector Conversion
• Schematic of the raster vector conversion by
which left and right polygons are identified