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Making friends with IDL

Making friends with IDL. IDL = interactive data language. interactive environment. immediate access to all variables. excellent for visualizing, analyzing, editing, and displaying numerical data sets. optimized array operations. versatile built-in plotting and graphics routines.

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Making friends with IDL

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  1. Making friends with IDL IDL = interactive data language interactive environment immediate access to all variables excellent for visualizing, analyzing, editing, and displaying numerical data sets optimized array operations versatile built-in plotting and graphics routines data structures possible interface with C and Fortran routines on line help (?) IDL LIMITATIONS: IDL is an interpreted rather than a compiled language. This means that large IDL programs can execute less rapidly than equivalent compiled programs written in FORTRAN or C. IDL is a proprietary system (need licence)

  2. Making friends with IDL create variables > name = ‘Maxwell’ creates a string > z = 1.0e-8 creates a scalar > testdata = fltarr(512,512) creates a 512x512 2-D array with zero entries > a = [1,2,3] createsa vector > a = [a,4] expands a vector Warning: If you redefine a variables during your work, you lose the previous values Avoid operation with different variables types. For example using float and integer these could be different > print, 3.456 * 1 > print, 3.456 * 1.

  3. Variables Variable names can have letters, numbers and underscores in them. They are NOT case-sensitive: aaa, Aaa and AAA are all the same variable. One dimension array of 6 elements = Array[6] IDL> a=[3, 5, 6, 2.5, 100, 27.7] Array index START FROM 0!!!! IDL> a= [[ 2,3,4],[10,20,30]] Array of 2 rows and 3 columns = Array[3,2] IDL> a=float(b) IDL> a=fltarr(n_elements(b),4,2)‏

  4. Array manipulations (a b c)# (g h) = (ag+dh bg+ch cg+fh) (d e f) (i j) (ai+dj bi+ej ci+fj) (k l) (cg+fh ci+fj ck+fl) > a = [1,2,3] > b = [4,5] > print, a#b > print, b#a > print, a##b > print,a*b > print,a+1 > print,b*2 > print,a+b (a b c)## (g h) = (ag+bi+ck ah+bj+cl) (d e f) (i j) (dg+ei+fk dh+ej+fl) (k l) Warning!!! INVERT - Computes the inverse of a square array. MAX - Returns the value of the largest element of Array. MEDIAN - Returns the median value of Array or applies a median filter. MEAN – Return the mean value (also first element of MOMENT). MIN - Returns the value of the smallest element of an array. MOMENT – compute the first 4 moments (mean, variance…) REFORM - Changes array dimensions without changing the total number of elements. REVERSE- Reverses the order of one dimension of an array. SIZE- Returns array size and type information. TOTAL - Sums of the elements of an array. TRANSPOSE - Transposes an array. WHERE- Returns subscripts of nonzero array elements. t=0 for i=0,n_elements(a)-1 do t=t+a(i) Try to avoid loops t=total(a)

  5. looking for help ? name Open a help on line windows and search for ‘name’ print,max(a); print,min(a); print,max(a); print,mean(a); print,variance(a); print,median(a); print,moment(a): print various statistical properties of image array. (moment prints first four moments.) print • help,variable : print variable informations. • help,A,/str : print structure info • help,/rou : prints list for all compiled procedures. Lists procedure and functions separately. • help,/sy : prints current values of all "system variables", which are special variables known to all routines. Names of these begin with a "!", e.g. !dir, !path, etc. • help,/rec : prints contents of command recall buffer in reverse order • help,/dev : prints parameter settings for current graphics device • help,/mem : lists current memory usage help

  6. Saving data (and time!) Safety idea: save your data!!! Be prepared: 99% of time you will have to redo plots. Usual sequence: 1) Make plot 2) Save data (and exit from idl) 3) Meeting 4) Restore data 5) Redo plot It will help also have your code saved in a routines. make a routine! save > save,variable1,variable2,variable3,filename=‘~elisa/idl/data.sav’ Keyword: ALL => save all common block, system variable and local variable from the current IDL session. > save,/all,filename=‘datatemp.sav’’ restore • restore, filename=‘~elisa/idl/data.sav’ • > restore,filename=‘datatmp.sav’

  7. IDL routines (.pro) As you type, each line is interpreted and immediately executed OR How to call it .pro file requirement main routine for (loop), if, case... ... end > .r filename without .pro procedures or subroutines pro NAME, VARIABLES ... end > name, variables parameters and keywords NAME,input1,input2...output1,output2...keyword1=value1,$ keyword2=value2, /Keyword3.... optional and can be in any order function NAME,VARIABLES ... return,VALUE end > a = name (variables) functions One of the best ways to learn how to write and use IDL programs is to look the existing IDL programs

  8. Program execution (and other) Values of keywords are usually determined by assignment statements: PROCEDURE_NAME,parm1,parm2.....KEYWORD1=100.,KEYWORD2='dumbo',... in the case of switches, keywords can be set to a value of 1 by using the following syntax: NAME,parm1,parm2...../KEYWORD1,..... all IDL procedures/functions are assumed to be in files with the explicit extension '.pro'. Run from IDL prompt compiles the IDL procedure(s) or function(s) in the file [name].pro. If this is a main program, also executes it. >.r or .run [name] WARNING!!!! IDL will locate the first file with this name in the IDL path or current directory Inside a file.pro Compile the file_name.pro Useful if the file mane is different from the procedure name @file_name stop for debugging!! ... print... plot... to continue > .c or .con ; comment Don’t forget the comments!!! Comments begin with ‘;’ if you wont to come back to the first level > retall

  9. Structures A structure can be thought of as a user-defined data type or groups of different data IDL allows you to put lots of variables into a single ‘structure’ For example satellite data can be load as a structure containing: Instrument name, data and time, pixels radiances, coordinates and observing angles of the pixels A structure (e.g. dsat) is an ensamble of other, previously defined, variables (and structures) Define a structure: dsat={aod550:aot,$ ; mean AOD stdaod550:sigma,$ ; standard deviation n:num,$ ; number of points latc:latitude,$ ; central lat of the boxes lonc:longitude} ; central longitude of the boxes > help, dsat,/str AOD550 DOUBLE Array[720, 360] STDAOD550 DOUBLE Array[720, 360] N LONG Array[720, 360] LATC DOUBLE Array[360] LONC DOUBLE Array[720] To access the variables of a structure Use: mone_str.nome_var > print,dsat.aod550(good) Routine that read satellite data usually load a structure for any image/orbit keep related variables together pass/return a lot of variables with only one name

  10. Basic plots window,0,xsize=300,ysize=200 x=findgen(10)‏ seed=1l n=32 x=randomu(seed,n)‏ y=randomu(seed,n)‏ y2=randomu(seed,n)‏ plot,x,y,psym=1,title='Random XY Points' oplot,x,y2,psym=2,colour=2 IDL> print,x 0.000 1.000 2.000 3.000 4.000 5.000 6.000 7.000 8.000 9.000 x2=2*!PI/100*findgen(100)‏ IDL> plot,sin(x2)

  11. Others useful things cut of datawhere Logical operator good = where (time eq 1000.,count) if (count eq 1 ) then begin... If (count gt 1) then begin plot, x(good), y(good) endif and             ; and ...or              ; orgt              ; greater than (similarly lt)ge              ; gt or equal to (similarly le)eq              ; equal tone              ; not equal to set_plot, 'ps' device, filename='filename.ps‘ … close, /device set_plot, 'x' print on postscript .ps file plotting commands Smaller file, good to make presentations and movies, NOT good for reports and papers !!! save a window like .jpg a = tvrd(true=3) write_jpeg, 'namefile.jpg',a,true=3 png? ‘comp_map_'+sat1+'_vsall.jpg’

  12. routines at AOPP ASK!!! /home/crun/eodg/idl/ Linear fit when both x and y have errors (y = A + B x) fitexy,px,py,A,B,X_SIG=X_SIG,Y_SIG=Y_SIG Plots data points, with defined latitudes and longitudes mappoints,data,lat,lon,centre=[0,0],/nogrey,nlevels=100 Interpolate data (with the associated lat,lon) onto a regular lat lon grid, and plot the image imagepoints,data,lat,lon Using the same some fast regridding code (RAL) ncol=4 nrow=4 !P.MULTI= [0,ncol,nrow,0,0] avgrid,lat,lon,aod Load txt file in columns mappoints,dayav.AOD550,lat,lon,centre=[0,0],/nogrey,$ Nlevels=100,range=range,symsize=0.6,$ title='AOD all daset average '+strcompress(i+1)+' March 2006' loadxy loadxyz colour_ps Set colour bar tvdata + several routine to load different type of data

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