Basic of Programming in GIS

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Basic of Programming in GIS

• Presentation by Programming Group (3)
• Jon Remo
• Mayank Srivastava
• Zhigang Wang

2
Outline

• Programming Basics
• Data types
• Variables
• Arrays and Matrices
• Loop Structures
• Decision Structures
• Functions and Subroutines
• Visual Basic Applications
• VBScript
• VBA
• Macros in Excel
• Marcos is Arc GIS

3
Outline (contd)

• Programming and GIS
• AML
• Avenue
• Arc Objects
• MapInfo
• MapBasic Window

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DATA TYPES

• Data field types Size VBType
  Comments
• Integer 2
  Integer 32768
• Long 8
  Long 2147483648
• Single 4
  Single
• Double 8
  Double Floating Points
• Currency 8
  Currency Fixed point
  calculation

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Data Types Contd..

• String V String
  Text Character
• Byte 1 Byte
  Stores 0 to 255 only
• Boolean 1 Boolean
  Stores 0 or 1 only
• Date 8 Date/Time
  Date left-decimal-time right
• Object 4 Object Holds programming
  statement.
• An element from VB program
• Variant 16 Variant Numeric 16 bytes and text
  22 bytes.

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Declaring Variables and Scope

• Variables - used to hold and manipulate values or
  data needed by an application.
• In VB a variable must be declared before it is
  used in the code.
• Variable can only hold the declared data type.
  (exception variant data type)

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Declaring Variables and Scope

• Scope
• Refers to the availability of a variable from
  within the application's code.
• Variable scope and procedure scope
• Variable scopes in keywords DIM, Public,
  Private, ReDim, Static, Type.
• Procedure scopes in keywords Private, Public,
  Friend and static

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Declaring Variables and Scope

• Variable Scope
• DIM declares the variables by assessing them a
  name and data type.
• DIM Number as Integer
• Public Keyword makes a variable global through
  out the entire application.
• Private Variable (Local) only visible in a
  procedure in which you declare it.
• ReDim- reallocate storage space for dynamic array
  variables
• Static preserve its value between procedure
  calls.
• Type declare a user type

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Declaring Variables and Scope

• Procedure Scope
• Private specify a subroutine or function is
  private to the modules or forms in which it is
  declared.
• Private Function Return()
• Dim Retval as Integer
• Retval 7
• RetvalRetval 2
• Msgbox Retval
• End Function
• Public specify a subroutine or function is
  global to all forms and modules.

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Declaring Variables and Scope

• Constants a numeric or string value that does
  not change through the execution of a program.
• Declared by command CONST
• Const MAXMARK as INTEGER 100
• Public Const ROAD1 as string Stewart
• Option Explicit
• Statement tells Visual Basic that the rest of the
  code in this module is to declare all variable
  before they are used. ( e.g. catch variable name
  error)
• To force variable declarations to be explicit
  (i.e. each variable be declared), add option
  explicit statement at the module or form level.

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Arrays and Matrices

• Array -variable containing multiple values.
• Values that all have the same data type in an
  array.
• Matrices Multidimensional arrays - one name,
  can only hold one data type declared in the
  matrices.

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Arrays and Matrices

• Examples
• Single Dimension Arrays
• Dim Vals(3) as Integer
• Vals(0)10
• Vals(1)30
• Vals(2)50
• Matrices (multidimensional arrays)
• Dim Vals(2, 2) as Integer
• Vals(0, 0) 10
• Vals(0, 1) 20
• Vals(1, 0) 30
• Vals(1, 1) 40

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Arrays and Matrices

• Option Base statement sets the lower bound for
  all arrays.
• Default value 0 (option base 0)
• Option Base 1 Set the lower bound value of the
  array as 1.
• Upper and lower bounds Give a range to array
  indexing.

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Arrays and Matrices

• Getting Data into and out of Arrays.
• Private Sub Command1_Click()
• Dim Vals(3) As Integer
• Vals(0) 10
• Vals(1) 30
• Vals(2) 50
• Vals(3) Vals(0) Vals(1) Vals(2)
• MsgBox Vals(3)
• End Sub

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Visual Basic

• Based on - BASIC
• (Beginners all purpose symbolic instruction
  codes)
• Interpreted and compiled language- allows to run
• programs as it is written.
• More suited to windowed environment
• Graphic Based

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Visual Basic Interface

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VBScript

• Based on Visual Basic
• It is a medium through which HTML documents
  locates and executes Visual Basic ActiveX
  applications.

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Loops Structures

• For Next Loop
• Do Loop
• Do while.. Loop
• Do . Loop While
• Do Until Stop
• Do . Loop Until

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Loops Structures ( example)

• I1
• S0
• For I1 to 10
• ss1
• Print S
• Next I

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Decision Structures

• If Then
• If Then Else
• Select Case
• Combining Structures

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Decision Structures (Example)

• If condition1 then
• outcome1
• Else
• If condition2 then
• Outcome 2
• End If

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Functions and Subroutines

• Function sends a value called a return value to
  another location in the program when called upon.
• Subroutines does not send a return value, but
  does perform work through its code.

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Visual Basic for Application

• Macro in Excel

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Macros ArcGIS

• Visual Basic for Applications (VBA) - embedded in
  ArcMap and ArcCatalog.
• Allows for writing, debug, and testing of the
  Marco immediately.

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Example of Marcos in ArcGIS
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AML (Arc Macro Language)

• Procedural language
• Tasks are carried out in a serial order.
• Used with ArcInfo.

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AML Example

• / --------
• / beep.aml
• / --------
• /
• / Produces an audible 'beep', useful to attract
  attention to errors, etc.
• /
• / History
• / October 1998 Original coding - Stephen Lead
• /
• / -----------------------------------------------
  ----------------------------
• / We need to know what operating system we're
  using.
• s system extract 1 show os
• / If it's Windows we use G, which is
  achieved by typing ALT-007.
• if system Windows_NT then sys echo
• / For UNIX, the following command will do it.
• else sys /usr/bin/echo "\07"

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Avenue

• Arc View GISs scripting language.
• An object oriented program language.
• Provides a higher degree of uniformity, stability
  and reusability.
• Encapsulation
• Polymorphism
• Inheritance

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Example of Avenue
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ArcObjects

• The development plate form for the ArcGIS family
  of applications.
• Provides an infrastructure for application
  customization
• Built using Microsofts Object Model technology.

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Alternatives to ArcGIS

• MapInfo
• Software package designed to associate with
  geographical or spatial locations.
• Used more wide spread in business applications.
• MapBasic
• A development environment containing a text
  editor, compiler, linker and online help.
• The language is structured after VB

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Alternatives to ArcGIS

• MapBasic Window

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References

• http//www.esri.com/, 2004.
• Environmental Systems Research Institute, Inc.,
  1997 Understanding GIS The ARC\INFO Method 4th
  eds., Redlands, California.
• Ralston, B. A., 2002, Developing GIS Solutions
  with MapObjects and Visual Basic OnWord Press,
  Albany, New York.
• Razavi, A. M., 1999, ArcView GIS/Avenue
  Developers Guide 3rd ed., OnWorld Press,
  Albany, New York.
• Wells, E., and Harshbarger, S., 1997, Microsoft
  Excel 1997 Developers Handbook Microsoft Press,
  Redmond Washington.
• Whitener, A., Ryker, B., 1997, MapBasic
  Developers Guide OnWord Press, Santa Fe, New
  Mexico.