Basic IDL Commands

1
Basic IDL Commands

• SIMG 726

2
Objective

• Quick Tour of IDL
• Writing IDL Programs

3
Before we start

• source rvrpci/.simg726.rc
• typescript
• set history100
• AT THE END OF THE UNIX SESSION,
• DONT FORGET TO TYPE
• D

4
Before we END

• AT THE END OF THE UNIX SESSION,
• DONT FORGET TO TYPE
• D
• You now have file called typescript which
  contains a log of your UNIX session

5
Starting IDL in UNIX

• To start command line interface IDL environment
• idl
• To start graphical interface IDL environment
• idlde

6
IDL Help

• MOST IMPORTANT IDL COMMAND OF ALL
• IDLgt ?

7
IDL Help Window
8
Other IDL Help Facilities

• IDLgt doc_library,moment
• Allows specially formatted code comments to be
  viewed without having to view the source code

9
General IDL Information

• N.B. Platform specific limitation
• UNIX
• File name conflict between lower and upper case
  characters
• e.g. addnum.pro vs. AddNum.pro
• Recommend use of strictly lowercase file names

10
IDL Character Set

• IDL is not case sensitive
• Commands and arguments are delimited by comas.
• e.g. IDLgt print, a
• Comments are started by a semicolon ()
• e.g. IDLgt This is a comment
• Command options are set using a backslash (/)
• e.g. IDLgt tv, a, /order

11
Other IDL Characters

• System variables are started with an exclamation
  point (!)
• e.g. IDLgt print, !PI
• e.g. IDLgt y sin( x!DTOR )
• Command line continuation with
• e.g. IDLgt print, 180 /
• !PI

12
Other IDL Characters

• Multiple IDL commands can be separated by the
  symbol
• e.g. IDLgt a0.0 b1.0
• UNIX Command execution
• e.g. IDLgt ls -la

13
Journal Facility of IDL

• The journal command allows you to record all IDL
  activity during a particular session
• IDLgt journal, sequence.pro
• IDLgt print, 35
• IDLgt journal

14
sequence.pro
IDL Version 3.6.1a (MacOS Macintosh) Journal
File for Rolando Raqueño_at_green Working
directory Raqueño's Hard DriveApplicationsENVI
Date Tue Sep 17 005618 1996 print,35
15
15
Sample Commands

• Some sample command
• IDLgt print,35
• IDLgt print,SysTime()
• IDLgt num 512
• IDLgt help,num
• NUM INT 60
• IDLgt print,num
• 60

16
Creating an Array

• Some sample command
• IDLgt num fltarr(40)
• IDLgt help,num
• NUM FLOAT Array(40)
• IDLgt print,num
• 0.00000 0.00000 0.00000 0.00000
  0.00000 0.00000 0.00000
• 0.00000 0.00000 0.00000 0.00000
  0.00000 0.00000 0.00000
• 0.00000 0.00000 0.00000 0.00000
  0.00000 0.00000 0.00000
• 0.00000 0.00000 0.00000 0.00000
  0.00000 0.00000 0.00000
• 0.00000 0.00000 0.00000 0.00000
  0.00000 0.00000 0.00000
• 0.00000 0.00000 0.00000 0.00000
  0.00000

17
Creating an Indexed Array

• Some sample command
• IDLgt for i0,39 do num(i)i
• IDLgt help,num
• NUM FLOAT Array(40)
• IDLgt print,num
• 0.00000 1.00000 2.00000 3.00000
  4.00000 5.00000 6.00000
• 7.00000 8.00000 9.00000 10.0000
  11.0000 12.0000 13.0000
• 14.0000 15.0000 16.0000 17.0000
  18.0000 19.0000 20.0000
• 21.0000 22.0000 23.0000 24.0000
  25.0000 26.0000 27.0000
• 28.0000 29.0000 30.0000 31.0000
  32.0000 33.0000 34.0000
• 35.0000 36.0000 37.0000 38.0000
  39.0000

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Shortcut Creating Indexed Array

• Some sample command
• IDLgt num findgen(40)
• IDLgt help,num
• NUM FLOAT Array(40)
• IDLgt print,num
• 0.00000 1.00000 2.00000 3.00000
  4.00000 5.00000 6.00000
• 7.00000 8.00000 9.00000 10.0000
  11.0000 12.0000 13.0000
• 14.0000 15.0000 16.0000 17.0000
  18.0000 19.0000 20.0000
• 21.0000 22.0000 23.0000 24.0000
  25.0000 26.0000 27.0000
• 28.0000 29.0000 30.0000 31.0000
  32.0000 33.0000 34.0000
• 35.0000 36.0000 37.0000 38.0000
  39.0000

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Indexed Array Example

• Some sample command
• IDLgt num findgen(40)10
• IDLgt print,num
• 0.00000 10.0000 20.0000 30.0000
  40.0000 50.0000 60.0000
• 70.0000 80.0000 90.0000 100.000
  110.000 120.000 130.000
• 140.000 150.000 160.000 170.000
  180.000 190.000 200.000
• 210.000 220.000 230.000 240.000
  250.000 260.000 270.000
• 280.000 290.000 300.000 310.000
  320.000 330.000 340.000
• 350.000 360.000 370.000 380.000
  390.000

20
Indexed Array Example

• Some sample command
• IDLgt num findgen(40)10-195
• IDLgt print,num
• -195.000 -185.000 -175.000 -165.000
  -155.000 -145.000 -135.000
• -125.000 -115.000 -105.000 -95.0000
  -85.0000 -75.0000 -65.0000
• -55.0000 -45.0000 -35.0000 -25.0000
  -15.0000 -5.00000 5.00000
• 15.0000 25.0000 35.0000 45.0000
  55.0000 65.0000 75.0000
• 85.0000 95.0000 105.000 115.000
  125.000 135.000 145.000
• 155.000 165.000 175.000 185.000
  195.000
• In general you will be using a linear form
• ymxb

21
Extracting Array Subset

• Some sample command
• IDLgt num1 num(036)
• IDLgt print,num1
• -195.000 -185.000 -175.000 -165.000
  -155.000 -145.000 -135.000
• -125.000 -115.000 -105.000 -95.0000
  -85.0000 -75.0000 -65.0000
• -55.0000 -45.0000 -35.0000 -25.0000
  -15.0000 -5.00000 5.00000
• 15.0000 25.0000 35.0000 45.0000
  55.0000 65.0000 75.0000
• 85.0000 95.0000 105.000 115.000
  125.000 135.000 145.000
• 155.000 165.000
• IDLgt help,num1
• NUM1 FLOAT Array(37)

22
Scalar Operation on Arrays

• Some sample commands
• IDLgt num findgen(37)10
• IDLgt print,num
• 0.00000 10.0000 20.0000 30.0000
  40.0000 50.0000 60.0000
• 70.0000 80.0000 90.0000 100.000
  110.000 120.000 130.000
• 140.000 150.000 160.000 170.000
  180.000 190.000 200.000
• 210.000 220.000 230.000 240.000
  250.000 260.000 270.000
• 280.000 290.000 300.000 310.000
  320.000 330.000 340.000
• 350.000 360.000
• IDLgt help,num
• NUM FLOAT Array(37)

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Two-Dimensional Plotting

• Displaying Two-Dimensional Graphics
• IDLgt line Sin(num !DtoR)
• IDLgt plot,line

24
Two-Dimensional Plotting

• Displaying Two-Dimensional Graphics
• IDLgt plot,line IDLgt plot,num,line

25
Two-Dimensional Plotting Options

• IDLgt plot,num,line,/Psym

26
Two-Dimensional Plotting Options

• IDLgt plot,num,line,Psym1

27
Other Plotting Options

• IDLgt plot,num,line,linestyle1

28
Labeling IDL Plots

• IDLgt plot,num,line,xrange0,360,
• ytitle'Sin(x)',Title'Sine Plot'

29
Other Plot Facilities

• IDLgt plot,num,line,xrange0,360,
• ytitle'Sin(x)',Title'Sine Plot'
• IDLgt plots,0,360,0,0

30
Polygon Filling

• IDLgt loadct, 5
• IDLgt polyfill,num(018),line(018),color120
• IDLgt polyfill,num(1836),line(1836),color50

31
Data File Inputs

• Copy the following files from
• rvrpci/pub/IDL/training
• surface.dat
• ctscan.dat

32
Three-Dimensional Plotting

• Displaying Three-Dimensional Graphics
• To get the data into IDL, you will need to open a
  file and read it into an array using the
  following commands (N.B. this is specific for
  this particular data set)
• IDLgt filesurface.dat
• IDLgt openr,lun,file,/get_lun
• IDLgt peakfltarr(40,40)
• IDLgt readf,lun,peak
• IDLgt free_lun, lun

33
Surface Plots

• Displaying Three-Dimensional Graphics
• IDLgt print, max(peak), min(peak)
• IDLgt surface,peak

34
Surface Plots

• IDLgt x findgen(40)2.5 yfindgen(40)50
• IDLgt surface,peak,x,y

35
Color Look-up Tables

• The following command lets you view the current
  colors loaded into the color look-up tables
• IDLgt cindex

36
Background/Foreground Colors

• The following surface command lets you manipulate
  the background and foreground colors
• IDLgtsurface,peak,background200,color45,
• title'Surface Projection',charsize2.0

37
Shaded Surface Plotting

• IDLgt shade_surf, peak

38
Draping Data Over a Surface

• We can drape a given surface over another one by
  the following command (we read in the data snow
  the same manner as peak)
• IDLgtshade_surf,peak,
• shadesnow

39
Surface Plot Colored by Altitude

• We can generate a simple elevation color map.
• IDLgt shade_surf, peak, shadebytscl(peak)

40
Simple Contour Plots

• We can generate a simple contour map.
• IDLgt contour,peak

41
Contour Plots Spacing

• We can generate a simple contour map and adjust
  spacing.
• IDLgt contour, peak, nlevels10

42
Contour Plots Labelling

• We can generate a simple contour map and label
  them
• IDLgt contour, peak, nlevels10, /follow

43
Contour Plots Spacing Adjustment

• We can generate a simple contour map and adjust
  spacing along with line styles.
• IDLgt contour, peak, nlevels10, c_linestyle
  indgen(5)

44
Colored Contour Plots

• We can generate a simple contour map and adjust
  spacing along with line color.
• IDLgt contour, peak, nlevels10, c_colors
  indgen(5)2080

45
Images Data

• Displaying Image Data
• You can read in image data in a manner similar to
  other forms of two-dimensional data. You will
  need to ascertain whether the data is an ASCII
  file or a binary file
• IDLgt openr, lun,ctscan.dat,/get_lun
• IDLgt scanbytarr(256,256)
• IDLgt readu, lun, scan
• IDLgt free_lun, lun

46
Image Data

• Displaying Image Data
• IDLgt window, /free, xsize256, ysize256
• IDLgt tvscl, scan

47
Image Data

• Displaying Image Data
• IDLgt window, /free, xsize256, ysize256
• IDLgt tvscl, scan IDLgt tvscl,hist_equal(scan)

48
Image Processing

• Displaying Image Data
• IDLgt window, /free, xsize256, ysize256
• IDLgt tvscl, scan IDLgt tvscl, sobel(scan)

49
XLOADCT Routine

• Displaying Image Data
• IDLgt xloadct
• IDLgt tvscl, scan

50
Writing IDL Programs
51
General Form of an IDL Program

• Parts of an IDL program
• pro program_name , arg1, arg2, ..., argn
• IDL statement 1
• IDL statement 2
• .
• .
• .
• IDL statement n
• end

52
Compiling an IDL Program

• Create a program to take celsius arguments and
  print out fahrenheit values
• pro celsius_to_fahrenheit, celsius
• print, 9/5celsius32
• end
• To compile
• IDLgt .compile celsius_to_fahrenheit.pro

53
Executing an IDL Program

• To use the program in scalar mode
• IDLgt c 100.0
• IDLgt celsius_to_fahrenheit, c
• To use the program in array mode
• IDLgt c findgen(201)/2
• IDLgt celsius_to_fahrenheit, c

54
General Form of an IDL Function

• Parts of an IDL function
• function program_name , arg1, arg2, ..., argn
• IDL statement 1
• IDL statement 2
• .
• .
• .
• IDL statement n
• return, answer
• end

55
Compiling an IDL Function

• Create a function to take celsius arguments and
  print out fahrenheit values
• function celsius_to_fahrenheit, celsius
• answer9/5celsius32
• return, answer
• end
• To compile
• IDLgt .compile celsius_to_fahrenheit.pro

56
Executing an IDL Function

• To use the program
• IDLgt c findgen(201)/2
• IDLgt f celsius_to_fahrenheit(c)
• IDLgt print, f
• IDLgt plot, c, f
• Equivalently
• IDLgt print, celsius_to_fahrenheit(c)
• IDLgt plot, c, celsius_to_fahrenheit(c)

57
Program Designprogram file vs. function file

• Use functions in case of mathematical functions
  to allow composition of functions
• IDLgt kcelsius_to_kelvin(fahrenheit_to_celsius(f))
  
• Use program file in case of process not requiring
  the return of data
• IDLgt write_to_file,temperature.dat,k

58
Parameter Passing in IDL

• IDL passes parameters into functions and programs
  by reference
• This means parameters can be modified through
  side effect
• pro celsius_to_fahrenheit, celsius
• celsius 9/5celsius32
• end

59
Problems with Side Effect Parameter Passing

• IDLgt a32.0
• IDLgt celsius_to_fahrenheit,a
• Compiled module CELSIUS_TO_FAHRENHEIT.
• IDLgt print,a
• 64.0000

60
A Debugging Exercise

• The IDL function and program examples
  celsius_to_fahrenheit all compile, but generate
  incorrect answers in some cases.
• This is left as a debugging exercise

61
Hints for Statistics Problem

• Study the IDL functions
• n_elements()
• size()
• Try to reuse as many of the functions as
  possible.
• Do not be concerned with efficiency at this point.