Introduction%20to%20IDL

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Introduction to IDL

• Lecture 2

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ITT solutions for data visualization and image
analysis

• http//www.ittvis.com/
• IDL, programming language
• ENVI, image processing based on IDL

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IDL

• Data visualization and image analysis
• IDL has both numeric and nonnumeric data types
• IDL is an array-oriented language
• Build-in functions
• Command Line and Development Environment

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Array-oriented language

• One dimension array (or vector)
• array1.0, 2.0, 4.0, 8.0 or array (4)
• Two dimension array (or matrices, one band
  image)
• Array1,2,3, 5,7,8 or (Array (3,2))
• Three dimension array (multiple bands image)
• Arrayfindgen(500,300,6) or an image of 500
  columns, 300 rows, and 6 bands
• Any operation on an array is performed on all
  elements of the array, without the need for the
  user to write an explicit loop. The resulting
  code is easier to read and understand, and
  executes more efficiently.
• For example, you have a landsat image of (500,
  300, 6) (i.e. column, row, bands) and you wish
  to divide each pixel (or element) by 2 or do
  other calculations
• Imageimage/2
• Print, total(image) / n_elements(image)
• Print, mean(image) the same as above

(c, r, b) BSQ (b, c, r) BIP (c,
b, r) BIL
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• Compact syntax without using loops. This makes
  simpler coding and the processing much faster
  than loops
• npts1000000L
• datarandomu(0L, npts)
• sumtotal(data)
• sum0.0
• for i0L, (npts-1L) do sumsumdatai

Randomu Return a array of uniformly distributed
random numbers (0,1) of the specified dimensions
Needs 0.11 second
Needs 2.64s
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Functions for array creation

• Zeroed array ( arr() )
• bytarr(), intarr(), uintarr(), ulonarr(),
  ulong64arr(), fltarr(), dblarr(), complexarr(),
  strarr()
• Index array
• bindgen() byte index array
• indgen() integer index array
• ul64indgen() unsigned integer array
• ulindgen() unsigned long integer array
• lindgen() long integer index array
• l64indgen() 64-bit integer array
• findgen() Floating-point index array
• dcindgen() double precision floating-point index
  array
• cindgen() complex index array
• dcindgen() complex, double-precision index array
• sindgen() spring array

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Array indexing

• array dimension myarr(),
• array indexing myarrindex
• Two dimension can be
• 1-d linear indexing
• Arr1456
• 2-d indexing
• Arr2,356

Arr indgen(4,4)4 Print, arr 0 4
8 12 16 20 24 28 32 36 40 44
48 52 56 60 Print, arr3,2
44 Print, arr11 44 Print, arr(,2),
arr(2,) ?
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Array properties-build in functions

• n_elements(), size(), min(), max(), mean(),
  variance(), stddev(), moment(), total()

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Other operations for an array

• Locating values within an array
• Array reordering
• reform(), reverse(), rotate(), transpose(),
  shift(), sort(), uniq()
• Array resizing
• rebin(), congrid(), interpolate(),

Arr indgen(9)10 Index where(arr gt
35) Print, arrindex ?
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Other build-in functions and procedures

• FFT(image, -1), forward fast Fourier transfer
• FFT(image, 1), inverse FFT
• ROT(image, angle, scale, /sampling methods)
• interpolate, bilinear, cubic,
• map_image
• read_binary
• correlate
• .
• plot
• tv, tvscl
• contour
• .

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Command Line and Development Environment
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iTools

• Allow you to more quickly and easily open,
  analyze and visualize your data than even before.
• http//www.ittvis.com/idl/itools_tutorials.asp
• iPlot (plot)
• iSurface (surface)
• iContour (contour)
• iImage (tv, tvscl)
• iVolume (volume)
• iMap
• iVector

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IDL Virtual Machine

• Simple, no-cost method of distribution
• Run IDL6.0 .sav file programs without license
  requirements
• Commercial and non-commercial applications

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IDL/ENVI programming

• Combine the ENVI/IDL together, extending the ENVI
  interface in IDL in order to implement new
  methods and algorithms of arbitrary
  sophistication is both easy and fun (M. Canty,
  2007)
• See an example and will give more examples as the
  class moving forward

DEMO!