FINAL Project Information

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FINAL Project Information

• Two Design Review presentations (10-15 minutes
  long)
• A Final Document of your Project (LaTeX)
• HTML Page Describing your Project
• Choice of Topic Due after break
• Teaming is Encouraged

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Final Project

• E-mail me your Final Project Topic after break
• E-mail should contain
• a half page abstract of your intended GUI
  design, and the problem domain that it addresses.

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Quiz 2 Topics

• RCS commands (ci and co)
• mv
• cp
• grep
• jobs

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Working with Data
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Representation of Information in a Computer

• All information in a computer is stored as a
  collection of bits
• A bit, also known as a binary digit, is a number
  represented in base 2. It can only be either a 1
  (one) or 0 (zero)
• Think of information as data with structure
• All the ones and zeros represented by the
  computer is data. How they are interpretted
  generates information (or garbage)

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Representation of Information in a Computer

• Information stored in a computer can represent
• Instructions
• Executable Programs
• Data
• Numbers - integers and real values
• Characters - ASCII, multinational characters
• Others - imagery, sound, etc.

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Representation of Information in a Computer

• Bits in a computer are usually grouped into the
  following units
• 4 bits 1 nibble
• 8 bits 1 byte or 1 ( char ) - a single
  character
• 16 bits 2 bytes or 1 ( short int, int ) -
  integer value
• 32 bits 4 bytes or 1 ( long int, int ) -
  integer value or 1( float) - real value
• 64 bits 8 bytes or 1 (double) - real value

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Representation of Information in a Computer

• Numbers can be represented as either integers or
  real values
• integers -5, 0, 125, -32767
• real 3.14159, -2.71828, -1.0e-20, 10.000
• Text is typically represented using the ASCII
  character set where each character is represented
  as a byte value.

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Representation of Information in a Computer
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Representation of Information in a Computer
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Line Delimiters on Different Systems

• UNIX System, lines delimited by linefeed
• designated as nl
• ASCII value of 012 or 10
• In MACS and PCs, lines delimited by carriage
  returns
• designated as cr
• ASCII value of 015 or 13
• Still other systems use a combination of carriage
  return-line feeds to delimit lines

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Common Cross PlatformFile Problem

• Some one gave you a text file created on a PC
  which you transferred to the UNIX system.
• You try to edit the file using vi, but vi
  complains that the line is too long
• Solution (A Stupid Unix Trick)
• cat old_file tr \015 \012 gt new_file
• This command translates all carriage returns to
  line feeds.

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Numbering Systems
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Converting Number Bases
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Converting Number Bases
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Negative Number Representation
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Converting a Negative Number into Binary using
2s Complement
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How Does This All Relate to Computers and
Programming
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1-bit Address Line and 1-bit Data Line Computer
Architecture
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2-bit Address Line and 1-bit Data Line Computer
Architecture
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1-bit Address Line and 2-bit Data Line Computer
Architecture
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2-bit Address Line and 2-bit Data Line Computer
Architecture
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8-bit Address Line and 8-bit Data Line Computer
Architecture
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In General
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Caveat on Multi-Byte Data

• When dealing with data that encompasses more than
  a single byte (e.g. integer value greater than
  255), you must know the endian of the data
• Endian represents how a machine interprets the
  significance of a set of bytes.
• There are big-endian machines and little-endian
  machines

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Caveat on Multi-Byte Data (Big Endian)

• Big Endian Machines (Suns, Motorolas) would
  represent the integer value 512 internally as two
  bytes in the following order.
• MSB LSB
• 00000010 00000000

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Caveat on Multi-Byte Data (Little Endian)

• Little Endian Machines (DECS, Intels) would
  represent the integer value 512 internally as two
  bytes in the following order.
• LSB MSB
• 00000000 00000010

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Caveat on Multi-Byte Data

• This is typically not a problem as long as you
  stay on the same machine.
• If you, however, start transferring data (e.g.
  images) in raw form from one machine to another,
  you will need to be aware of this situation.
• You can often transpose multibyte data using the
  dd utility (does not work for data spanning more
  than two bytes)

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Working with IDL Variables

• Variable names must start with a letter but can
  include, letters, digits, underscore or dollar
  characters.
• Variables are not case sensitive, i.e.,
• Celsius is equivalent to celsius

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Working with IDL Variables

• Variables in IDL have two important attributes
• Data type
• Attributes

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IDL Variable Data Types

• Undefined
• Integer Values
• Byte, Integer, Long Integer
• Floating Point Values
• Floating Point, Double Precision
• Single Precision Complex, Double Precision
  Complex
• String

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IDL Variable Data Structures

• Scalar
• Vector (one-dimensional array)
• Array (up to eight dimensions)
• Structure (combination of any mixture of data -
  Very Important in understanding Object-Oriented
  Programming Concepts)

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Initializing Scalar Variables

• byte_variable 0B
• integer_variable 0
• long_integer 0L
• float_variable 0.0
• double_variable 0.0D
• complex_variable Complex(0.0, 0.0)
• dcomplex_variable DComplex(0.0, 0.0)
• string_variable

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Initializing Array Variables

• byte_array bytarr( 256, 256, 3 )
• integer_array intarr( 256, 256 )
• long_array lonarr( 256, 256 )
• float_array fltarr( 256, 256 )
• double_array dblarr( 256, 256 )
• complex_array complexarr( 256, 256 )
• dcomplex_array dcomplexarr( 256, 256)
• string_array strarr(80)

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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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Initializing Array Variables

• Initializing Array with each element set to its
  subscript
• bindgen, indgen, lindgen, findgen, dindgen,
  cindgen, dcindgen, sindgen
• Only real parts of complex numbers are set to the
  subscripts
• An array of strings containing the numbers is
  created by sindgen

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Initializing Array Variables (make_array and
replicate)

• Make_array function is a general way of creating
  and initializing arrays
• arraymake_array(10,12,Value1,/Int)
• Replicate functions allows initialization of all
  elements of an array with a given variable
  (useful in structures)
• initial_value 1
• arrayreplicate(initial_value, 10,12)

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Structures in IDL

• Allows more abstract data types to be created
  from other basic data types
• Example
• Date data structure
• IDLgt adate, month0B, day0B, year0B
• IDLgt print,a
• 0 0 0

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Structures in IDL(Names Structure)

• Date Example (using a Named Structure)
• IDLgt a.month12
• IDLgt a.day25
• IDLgt a.year96
• IDLgt print,a
• 12 25 96
• IDLgt print,a.month
• 12
• IDLgt print,a.day
• 25
• IDLgt print,a.year
• 96

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Using Named Structures

• Date Named Structure Example
• IDLgt cdate
• IDLgt print,c
• 0 0 0
• IDLgt help,c
• C STRUCT -gt DATE Array(1)

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Anonymous Structures in IDL

• Anonymous Structures
• IDLgt dmonth1,day1,year97
• IDLgt print,d
• 1 1 97
• IDLgt ed
• IDLgt print,e
• 1 1 97

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Anonymous Structure Example

• Anonymous Structures
• IDLgt emonth'January',dayd.day,yeard.year
• IDLgt print,e
• January 1 97
• IDLgt e.month'December'
• IDLgt print,e
• December 1 97

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Querying Structures in IDL

• Determining Variable Structure
• IDLgt help,e,/structure
• Structure lt761058gt, 3 tags, length12, refs1
• MONTH STRING 'December'
• DAY INT 1
• YEAR INT 97

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Structures in IDL

• Determining Structure Characteristics
• IDLgt print,n_tags(e)
• 3
• IDLgt print,tag_names(e)
• MONTH DAY YEAR

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Array Manipulation in IDL

• Lets create an array representing a multiband
  image
• IDLgt imagebindgen(2,3,4)
• IDLgt print,image
• 0 1
• 2 3
• 4 5

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Array Manipulation in IDL

• image continued
• 6 7
• 8 9
• 10 11
• 12 13
• 14 15
• 16 17

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Array Manipulation in IDL

• image continued
• 18 19
• 20 21
• 22 23

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Array Manipulation in IDL

• Extract the first and last band of the image
• IDLgt print,image(,,0)
• 0 1
• 2 3
• 4 5
• IDLgt print,image(,,3)
• 18 19
• 20 21
• 22 23

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Array Manipulation in IDL

• Extracting the color or spectral vector of
  the first pixel
• IDLgt print,image(0,0,)
• 0
• 6
• 12
• 18

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Array Manipulation in IDL

• Assign band 1 to band 4
• IDLgt band1image(,,0)
• IDLgt image(,,3) band1
• Shortcut
• IDLgt image(,,3)image(,,0)

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Array Manipulation in IDL

• Subsectioning parts of an image
• IDLgt print,image(01,01,)
• 0 1
• 2 3
• 6 7
• 8 9
• 12 13
• 14 15
• 0 1
• 2 3

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Array Manipulation

• where function to find indices of elements that
  meet certain criteria
• IDLgtprint, where(image gt 5 and image lt 12)
• Use of other arrays to index other arrays
• IDLgtindiceswhere(image gt 5 and image lt 12)
• IDLgtimage(indices)-1
• Try the above as an exercise.

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