1. Interactive Data Language (IDL) This PPT includes some materials downloaded from Internet, please don’t circulate it out of the LAB

2. What is IDL? Interactive Data Language (IDL) is a programming language that is a popular data analysis language among scientists. IDL is the trusted scientific programming language used across disciplines to create meaningful visualizations out of complex numerical data (ITT). • 1970 – IDL’s predecessor, Laboratory for Atmospheric and Space Physics, CO • Used by • NASA • Lockheed-Martin • Medical Imaging Fields • Remote sensing

3. What is IDL??? A More Powerful MATLAB, also more expensive. A great tool for hyperspectral imaging! A fast tool for processing large images!! A great GREAT tool for ENVI programming!!!

4. Overview of IDL • A high-level interpreted programming language with vector and array primitives • Modern programming language • Flow control • Data structures • Objects • All operators and most functions work on scalar, vector or array data of any data type. • Data visualization tool, advanced built-in graphics • 2-D plots • Contour plots • Surface plots • Shaded surfaces • Gray scale/color images • Volume rendering, … • Multi-platform support • Unix: Sun, Hewlett Packard, Silicon Graphics, IBM • Linux, Microsoft Windows, Mac

5. How to Learn • Online Help • Google • http://www.idlcoyote.com/ • Practice & Practice

6. Basic Variable Types • Integers - 1 byte – byte data type (0..256) IDL> a=bindgen(1) - 2 bytes – integers data type (0..2562-1) IDL> b=indgen(1) & print,5/3 1 - 4 bytes – long integers (0..2564-1) IDL> c=lindgen(1) - 8 bytes – 64-bit long integers (0..2568-1) • Floating data types - 4 bytes – floats (exponent from-38 to 38) IDL>print,5./3. & y=float(3)/float(2) 1.66667 IDL> a=1.23456789 IDL> print,a,format=‘(f20.10)’ - 8 bytes – double-precision IDL> print,5d/3d 1.6666667 IDL> a=1.23456789d0 & print,a,format=‘(f20.10)’ IDL> xyouts,xloc,yloc,string(a,format=‘f(20.10)’) • Strings (Text) IDL>x=‘Hi there!!!’

7. Assignment Statements A = B + 1 • A has the same structure as B, with a data type equal to that of the most precise operand in the expression on the right hand side. In this case it could be any type except string. • If B is a vector or array then 1 is added to each element. A = 0 ; A is a 16 bit integer A = A * 0.5 ; A is now a 32 bit float B = A(*,3) ; B is equal to the 4th row of A A(*,3) = 0 ; Set all elements in 4th row of A equal to 0 • Examples: image = fltarr(512, 512) ; zero filled array b = image(0:127, 0:127) ; b is 128x128 array image(*,100) = findgen(512) ; replace row 100 plot, image(*,100) ; plot row 121 ; Display the power spectrum as an image tvscl, alog(abs(fft(image, 1)))

8. Naming Variables • Assign ‘readable’ variable names that make sense • Variable names must start with a letter - NO: 6a=“gamma” OK: a6=“gamma” • Variable names may not have spaces in them - NO: A 6=5 OK: A_6=5 • Some characters are illegal or have special meanings - NO: a@=5, a.b=5 (used for structures), A+=5, A#=5

9. Organizational structures • Scalars IDL> x=3. • Vectors IDL> a=[0,1,2,3] & print,a[1] 1 • Arrays (see IDL help for matrices) (index from zero) intarr(), fltarr(), dblarr(), strarr().indgen() IDL> q=intarr(2,2) 0 0 0 0 IDL> m=indgen(2,2) 0 1 2 3 IDL> print,m(0,1) 2 IDL> a=findgen(100,100) IDL> print,a[1,0] 1.00000 IDL> b=a[23:25,67:69] IDL> indx=where(a gt 10.) IDL> jndx=where(a[indx] le 100.) IDL> b=a[indx[ jndx]]

10. Array operations • Simple math operations (* by scalar, +, -); A 3-column by 2-row array: IDL> A = [ [0, 1, 2],[3, 4, 5] ,[5,6,7]] IDL>B=2*A 0 2 4 IDL>print, B 6 8 10 10 12 14 • More complex math • #, Multiply an array by another IDL> C=A#B • N_elements: Total number of elements in array IDL> n=n_elements(A) • Total(array): computes a sum of all elements • Min(array): outputs the min value; also Max • Minmax(array): outputs the min then max • Rebin: Resize array IDL> C=Rebin(A,6,6) • Eigenvec: finds eigenvectors

11. Basic Programming • IF-THEN BLOCK • IF (logical-statement) THEN something • IF (logical-statement) THEN BEGIN • Something • Other thing • ENDIF • IF (logical-statement) THEN BEGIN • Something • Other thing • ENDIF ELSE some-other-thing

12. Basic Programming • CASE • CASE name OF • Match_1: do-something • Match_2: do-other thing • ELSE: do-things not-matched • ENDCASE

13. Basic Programming • DO-loop • FOR n=0, number DO a[n] = fix(n) • FOR n=0, number DO BEGIN • a[n] = fix(n) • B[n] = 2.0*a[n]^2 + 4.0*a[n] + 6.0 $ • + 8.0*a[n]^(-2.5) • ENDFOR • NOTE: $ is for continuation.

14. Files and Input/Output Write data to a file, formatted OPENW, 1, ‘original.dat’ OPENW, 2, ‘noisy.dat’ PRINTF, 1, original PRINTF, 2, noisy CLOSE, 1 CLOSE, 2

15. Plot and Processing • Making a New Dataset noisy = ((RANDOMU(SEED, 200) - .5) / 2) original = SIN((FINDGEN(200)/35)^2.5) • Plot PLOT, noisy • Plot them together PLOT, original, THICK = 3, XTITLE = "Time", YTITLE ="Amplitude“ OPLOT, original+noisy

16. IDL Examples IDL> a = sin(findgen(100)/99. * 2 * !pi) IDL> help, a IDL> plot, a IDL> a = shift(alog(abs(fft(dist(256),1))),128,128) IDL> isurface, a