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

Digital image format Sequential and interleave Raster vs. vector 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

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

Header file ENVI header file Generation of 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

Exercise 2 Generic import: defining an ENVI header Managing files 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

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)

Map information Why and what is mapping Two named structure 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)

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

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)

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

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

Map information (cont.) TWD 67

Map information (cont.) TWD 97

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

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

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

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

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

Self test Repeat exercise 6 to generate the figure