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Chapter 1

Chapter 1. Reading Data Analysis and applications of remote sensing imagery Instructor: Dr. Cheng-Chien Liu Department of Earth Sciences National Cheng Kung University Last updated: 28 February 2005. Outline . Digital image format Header file Map information Vector data.

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Chapter 1

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  1. Chapter 1 Reading Data Analysis and applications of remote sensing imagery Instructor: Dr. Cheng-Chien Liu Department of Earth Sciences National Cheng Kung University Last updated: 28 February 2005

  2. Outline • Digital image format • Header file • Map information • Vector data

  3. Digital image format • Sequential and interleave • Band sequential (BSQ) • Band interleaved by Pixel (BIP) • Band interleaved by Line (BIL) • Raster vs. vector • ENVI image format • Flat binary file • A binary stream of bytes without embedded non-image data or structural elements of any type • Header file

  4. Exercise 1 • Reading known image formats • Open external file • Read Flkeys.tif • Load standard false color bands • Explain why changing the view of main image slows down the display • Finding the cursor’s location and data value • Understand the widget of cursor location/value • Pixel locator • Determine the pixel size by watching the map coordinates update • Enter a lat/lon coordinate

  5. Header file • ENVI header file • A small ascii text file that contains the basic information that ENVI must know in order to read the image data • Extension • Generation of header file • Importing file • Reading a generic format • Reading a native format (e.g. GeoTiff) • No change  save in memory • Change  save in disk • View and edit header file in ENVI

  6. Exercise 2 • Generic import: defining an ENVI header • Open image file: envidata/boulder/bldr_tm.dat • Input: 702 samples, 863 lines, 6 bands, 0 bytes offset, floating point data type, Host byte order, ENVI standard file type, BIP interleave, Band name = Band 1, 2, 3, 4, 5, 7 • Check cursor location/value  not georeferenced • Add map information • Reference pixel: (526, 645)  (480168.67E, 4427572.69N) • Projection: UTM, zone 13, North American 1927 • Pixel size = 30m x 30m • Wavelength: import ascii file  twave6.asc (two columns) • Managing files • Open image files: envidata/cup95av/cup95at.int • Wavelength locator • Available file list

  7. Self test • Repeat exercise 2 • Open image file: envidata/boulder/bldr_tm.dat • Input: 702 samples, 863 lines, 6 bands, 0 bytes offset, floating point data type, Host byte order, ENVI standard file type, BIP interleave, Band name = Band 1, 2, 3, 4, 5, 7 • Check cursor location/value  not georeferenced • Add map information • Reference pixel: (526, 645)  (480168.67E, 4427572.69N) • Projection: UTM, zone 13, North American 1927 • Pixel size = 30m x 30m • Wavelength: import ascii file  twave6.asc (two columns)

  8. Map information • Why and what is mapping • USGS map projections • Two named structure • ENVI_PROJ_STRUCT • Define a map projection • ENVI_MAP_STRUCT • Define the georeferencing for an ENVI file • Viewing current structure of projection • proj = ENVI_PROJ_CREATE() • help, proj, /structures • Name: any name except for UTM- or utm- files • Projection type: 38 types (see User guide, appendix D) • Projection params: (see User guide, appendix D) • Projection units: (e.g. deg = 6, feet = 2, meters = 0) • Projection datum: (see C:\RSI\IDL60\products\envi40\map_proj)

  9. Map information (cont.) • Viewing current structure of map • map_proj = ENVI_MAP_INFO_CREATE() • help, map_proj , /struct • proj: the ENVI_PROJ_STRUCT variable • mc: a 4-element double array, [position in the image in file coordinates, corresponding map coordinates] • ps: a 2-element double array, the pixel size in the sample and line directions • rotation • pseudo: a flag used to indicate that the image has not been projected • ENVI files related to map projections • map_proj.txt: required parameters up to 15 values • ellipse.txt: ellipse name, semi-major a, semi-minor b • datum.txt:datum name, ellipse name, delta X, delta Y, delta Z

  10. Exercise 3 • Getting map information • ENVI_OPEN_FILE, 'C:\RSI\envidata\enviprog\avhrr\fl_avhrr.img‘ • map_infor = ENVI_GET_MAP_INFO(fid=fl_fid) • help, map_infor, /struct • help, map_infor.proj, /struct • print, ENVI_TRANSLATE_PROJECTION_NAME(map_infor.proj.type) • Ref to User’s guide, appendix D • print, map_infor.proj.params[2:3] • print, 'pixel sizes = ', map_infor.ps • print, 'Units = ', ENVI_TRANSLATE_PROJECTION_UNITS(map_infor.proj.units)

  11. Exercise 4 • Converting coordinates between map projections • lat_lon = dblarr(2,50) • fname = ENVI_PICKFILE(filter='*.txt') • OpenR, unit, fname, /Get_LUN • ReadF, unit, lat_lon • Free_LUN, unit • print, lat_lon[*, 0:4] • geo_proj = ENVI_PROJ_CREATE(/geographic) • sanfran_params = dblarr(6) • sanfran_params[0:5] = [a, b, lat0, lon0, x0, y0] • The North America 1983 datum (see map_proj.txt) • Projection origin: 37 North Latithde and 122 West Longitude • False easting and northing will both be 500,000 meters

  12. Exercise 4 (cont.) • Converting coordinates between map projections • print, ENVI_TRANSLATE_PROJECTION_NAME('Polyconic') • sanfran_proj = ENVI_PROJ_CREATE(type=10, params=sanfran_params, name='WCoast Polyconic', datum='North America 1983') • help, /struct, geo_proj • help, /struct, sanfran_proj • ENVI_CONVERT_PROJECTION_COORDINATES, lat_lon[1,*], lat_lon[0,*], geo_proj, mapX, mapY, sanfran_proj • for i=0,49 do print, lat_lon[*,i], mapX[i], mapY[i], format='(4(F20.5))‘ • ENVI_ADD_PROJECTION, sanfran_proj, /write • Check the file: map_proj.txt

  13. Map information (cont.) • TWD 67

  14. Map information (cont.) • TWD 97

  15. Exercise 5 • Write an IDL program to convert coordinates between TWD67 and TWD97 map projections • Check file: C:\RSI\IDL60\products\envi40\map_proj\map_proj.txt • Specify the required parameters for • TWD67: 6378160.0, 6356774.5, 0.000000, 121.000000, 250000.0, 0.0, 0.999900, Hu-Tzu-Shan, TWD67 • TWD97: 6378137.0, 6356752.3, 0.000000, 121.000000, 250000.0, 0.0, 0.999900, WGS-84, TWD97

  16. Vector data • Vector data • Utilize a coordinate-based system to represent and locate physical elements such as points, lines, and areas • Vertices, arcs, polygons • Compact • Format supported by ENVI • Available vectors list • Vector parameters window

  17. Exercise 6 • Vector layer overlay and editing • File: envidata/vectors/washdc_x.bil • Display: 321 RGB • Georeference image data • Open vector file: cities.shp, roads.shp, counties.shp • Geographic Lat/Lon projection with WGS-84 datum • It doesn’t specify a projection into which the imported vector data will be converted! • Display vector • Editing vector displays • Edit layer properties: Associate attribute name • Display vector attributes • Vector parameter, option, vector information, scroll, select one to display • Vector parameter, edit, view/edit/query • Change column width • Sorting • Change highlight color

  18. Exercise 6 (cont.) • Vector layer overlay and editing (cont.) • Editing vector layers • Select road.shp • Model, edit existing vectors • Tool, pixel locator, (690, 860) • Add node • Accept change • Model, add new vector • Node handles on • Accept new polyline • Add attribute information • Vector parameter, edit, view/edit/query • Querying vector attributes • Vector parameters, Edit, query attributes, STATE_NAME == Virginia • Vector to raster conversion • Export active layer to ROIs • Overlay • Options, report area of ROIs, Miles2

  19. Exercise 7 • Generating image contour lines and overlaying vector layers • Read USGS DEM file • Mosaic and display • Contouring a DEM image • Overlay vectors on a 3-Dsurface view

  20. Self test • Repeat exercise 6 to generate the figure

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