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 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

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 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

6. 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)  ( E, N)
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)  ( E, N)
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 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)

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: , , , , , 0.0, , Hu-Tzu-Shan, TWD67
TWD97: , , , , , 0.0, , 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