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A brief introduction to IDL

A brief introduction to IDL. Greg Michael Planetology and Remote Sensing Institute of Geosciences Freie Universitaet Berlin. A brief introduction to IDL. Why IDL for planetary data processing? Array processing language Powerful visualisation facilities

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A brief introduction to IDL

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  1. A brief introduction to IDL Greg Michael Planetology and Remote Sensing Institute of Geosciences Freie Universitaet Berlin

  2. A brief introduction to IDL • Why IDL for planetary data processing? • Array processing language • Powerful visualisation facilities This short intro intended to give an idea about what IDL is • Some IDL basics • Arrays • File handling • Strings • Worked example: read a VICAR image and save it as a TIFF file Mars Express HRSC/OMEGA data workshop, St. Louis, 21-23 May 2008

  3. Arrays Easy to create: a=indgen(10) print,a Easy to manipulate (other languages typically require a loop to do this, with one iteration for each element): b=a*10 print,b Easy to introduce complex array operations. Here, a matrix multiplication: c=a#a print,c Easy to visualise: d=indgen(400)#indgen(400) tvscl,d Files To record an array in a file: openw,1,"D:\mydocs\tmp\a.tmp" writeu,1,a close,1 And to recover it: e=intarr(10) openr,1,"D:\mydocs\tmp\a.tmp" readu,1,e close,1 To check it’s correct: print,e Strings Variables which store text, e.g. s="this is a string" print,s Can also have string arrays: t=replicate(s,10) print,t print,transpose(t) And write them to a text file: openw,1,"D:\mydocs\tmp\t.txt" printf,1,transpose(t) close,1 IDL: some basics Mars Express HRSC/OMEGA data workshop, St. Louis, 21-23 May 2008

  4. Get the file http://hrscview.fu-berlin.de/mex4/0515/h0515_0000.ir4.50 Read the file header: filename="D:\mydocs\data\HRSC\0515\h0515_0000.ir4.04" openr,1,filename s=“” readf,1,s close,1 print,s The values are stored as a series of expressions separated by spaces key=strsplit(s,' ',/extract) print,transpose(key) print,transpose(key[0:10]) To get an individual value: val=strsplit(key[0],'=',/extract) print,val lblsize=val[1] Extract the image data Also need to obtain NL and NS in the same way im=bytarr(ns,nl) openr,1,filename point_lun,1,lblsize readu,1,im close,1 tvscl,im tvscl,congrid(im,300,700) Save the image as a TIFF file write_tiff,"D:\mydocs\tmp\im.tif",im And a small version as a jpeg: write_jpeg,"D:\mydocs\tmp\im.jpg",congrid(im,300,700) *** Help Press F1, or Help-Contents from the menu Function library E.g. strsplit, congrid, tvscl, write_tiff IDL example: extract image from VICAR file Mars Express HRSC/OMEGA data workshop, St. Louis, 21-23 May 2008

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