1. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam WFM 6202: Remote Sensing and GIS in Water Management Akm Saiful Islam [Part-B: Geographic Information System (GIS)] Lecture-3: Input of Geospatial Data December, 2006 Institute of Water and Flood Management (IWFM) Bangladesh University of Engineering and Technology (BUET)

2. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. 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.

3. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. 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.

4. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam Compare data acquisition methods

5. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. 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.

6. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. 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.

7. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam Selecting a digitizing technique

8. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. 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.

9. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam Major Types of Scanner

10. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam Performance of major scanners

11. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. 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)

12. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. 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.

13. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam Procedures of Aerial Phtogrammetry

14. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. 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.

15. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam Earth Observation Satellites

16. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam High Resolution Satellites

17. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. 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.

18. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam Advanced Technologies

19. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam Advanced Technologies (contd..)

20. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam

21. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. 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.

22. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam Conversion Vector to Raster trapezoid area can be applied to convert vectorized polygon to rasterized polygon with grid cells

23. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam Vectorization Vectorization refers to conversion from raster to vector data, which is often called raster vector conversion.

24. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam Raster Vector Conversion Schematic of the raster vector conversion by which left and right polygons are identified