Introduction to IDL

1
Introduction to IDL

• Lecture 2
• January 28, 2005

2
Research System Inc.

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

3
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

4
Array in IDL

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

Needs 0.11 second
Needs 2.64s
5
Functions for array creation

• Zeroed array ( arr() ) and
• Index array ( indgen() )

6
Array indexing

• array dimension myarr(),
• array indexing myarrindex or (myarr10)index

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,) ?
7
Array properties

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

8
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 ?