Maa123.490 Programming in GIS

1
Maa-123.490 Programming in GIS

• Lecture 3
• Application development and GUI programming

2
Some things from prev. lectures

• Istvans web-page ripping
• want to rip place names and numbers
• complicated HTML but all needed data seems to
  be on one line
• path to solution split the complex problem into
  two simple problems
• rip into an array all items that look like
  numbers _at_a _ /(\d\\-\.)/g
• rip into a variable the place name if
  (/cell\gt(\w)/) n 1
• combine and enjoy

3
OGR

• GDALs sister, for accessing and manipulating
  vector data
• Datasource
• 1 Layer
• 1 LayerDefn
• 1 Feature
• 1 Geometry
• 1 Point (polygons have Rings)
• 1 Field

4
OSR

• SpatialReference
• WGS84, EPSG, ...
• CoordinateTransformation
• GeometryTransform

5
Application development

• Software projects
• Files
• program build process
• version control systems
• internationalization (i18n)
• Graphics
• Gtk2ExGeo

6
Files

• basic documentation
• who made this, change log, how to install, how to
  compile, general info, ...
• for sysadmins
• for developers
• for those building extensions
• for ordinary users
• licence
• installation scripts and templates

7
More files

• source code
• header files, code files
• resource files
• user interface
• icons and images
• definitions
• Schemas, Parsers,
• documentation
• user manual

8
Program build process 1/2

• from developer to distribution
• for example generate parser code, generate
  configuration script
• configuration
• what is this system?
• what is and what isnt available on this system?
• perl Makefile.pl or ./configure
• compilation
• create machine instruction code and link it
  together as dynamically linkable libraries and/or
  executables
• make

9
Program build process 2/2

• testing
• is the code working as supposed (on this system)?
• make test
• install
• Place the library, executable, documentation, and
  development support files in their correct places
  (may have been defined in the configuration step)
• make install

10
Distribution files

• Source code package
• includes all files mentioned on two previous
  slides
• .tar.gz, .zip
• Compiled package
• Includes some of the files mentioned on the two
  previous slides
• .msi, .rpm, .deb

11
Version control

• Scenario
• Several developers working on single software
  project
• Code is written, bugs are found and corrected,
  new features are added, this happens continuously
• Project needs one authoritative source tree
• Debugging may require going back to old versions
• Branching

12
Internationalization

• Requiring people to learn english in order to use
  a computer is wrong and absurd
• Internationalization is hard
• Technical aspects
• Character set, date format, decimal point ,
  currency, sorting,
• Practical aspects
• Language,
• Cultural aspects
• Fonts, colors,

13
Graphics issues in geoinformatics

• Graphics display is (in practise) always to a
  raster display

14
GIS graphics pipeline, from geodata..
geodata - rasters - objects
overlay process - coordinates - order - opacity
rendering - colors - fonts - line widths ...
15
.. to display buffer and/or screen
display buffer
window on screen
16
Using graphics in your own programs

• ..own programs with a GUI
• GUIs
• GUI toolkits
• digging in

17
GUI

• Graphical User Interface
• a method of interacting with a computer through a
  metaphor of direct manipulation of graphical
  images and widgets in addition to text
• pros you see what you have
• cons the freedom that is easy to achieve in CLI
  is very hard in GUI
• CLI command line interface

18
Widgets

• Graphical component or control
• button, check-box, radio button, combo box, icon,
  input field, tooltip, scrollbar, status bar,
  toolbar, menu (different types), window
  (different types)
• widget toolkits
• application ? its graphical appearance

19
Architecture
Look feel, inter- operability
Desktop environment window manager
Mac OS X, GNOME, KDE
Widget toolkit(s)
functionality
MacApp, MFC, Motif, GTK
Graphics/Window system
hardware abstraction
Windows
X
OS kernel
GNU
processing
Linux
devices
20
GTK

• A multi-platform toolkit for GUIs (widget
  toolkit)
• basis of GNOME
• used by, e.g., Dia and GIMP
• based on
• Glib low-level core library
• Pango library for layout and rendering of text
• ATK accessibility library
• written in C/C but with, e.g., Perl and Python
  in mind
• Glade GUI for developing GUIs with GTK

21
Simplest possible GTK-Perl application

• use Gtk2 '-init'
• my window Gtk2Window-gtnew
• window-gtshow_all
• Gtk2-gtmain

make the window visible
go into the event loop
22
Events, signals

• 1. User interacts with the application
• 2. Go to the widget, where the event occurred
• 3. A generic event signal is sent
• if that signal handler returns TRUE, stop
• 4. A specific event, e.g., button_press_event is
  sent
• if that signal handler returns TRUE, stop
• 5. Go to the widgets parent widget and repeat
  from 3. or give up if this is the top level widget

23
Notes, callbacks

• Not all widgets can receive events
• Parent is the widget in which the child is placed
• The widget sends the signal to the function(s)
  which is connected for the given signal
• user supplied callback possibly a default
  handler

24
our first callback
the widget to which we connect this callback

• window-gt
• signal_connect (
• "destroy",
• sub exit(0)
• )

the method, common to all widgets
the signal
the callback anonymous function
25
our second callback

• my event_box Gtk2EventBox-gtnew
• event_box-gtsignal_connect(
• button_press_event gt \button_press_event)
• event_box-gtadd(image)
• sub button_press_event
• my (widget,event) _at__
• print event-gtx," ",event-gty,"\n"

image cannot receive events
26
GUI design

• Glade
• glade-2
• use Gtk2 '-init'
• use Gtk2GladeXML
• Gtk2GladeXML-gtnew("gui4.glade")
• Gtk2-gtmain

27
Gtk2ExGeo project

• Put geodata to a GTK widget
• Current design (next page)
• Gtk2ExGeoGlue
• implement simple basic functionality with other
  Gtk2ExGeo modules other Gtk2 widgets
• basic functionality comes from libral, which is a
  C library

28
Gtk2ScrolledWindow
Gtk2GdkPixbuf
Gtk2ExGeoOverlay
Gtk2ExGeoRenderer
Layer (abstract)
GeoRaster
GeoVector
Gtk2ExGeoComposite
ogr
gdal
29
libral

• code for simple in-memory vector data
• simple rendering
• import from ogr (one feature at a time)
• code for simple in-memory raster data
• integer and real rasters
• raster algebra
• import from gdal (a viewport)
• code for rendering vector and raster data onto a
  GDK style pixbuf

30
GeoRaster

• Perl interface to a libral raster
• raster algebra overlayed
• a b is a raster if a and/or b is a raster
• implements the abstract class / interface Layer
• does not inherit from gdal, may contain a gdal
  object

31
GeoVector

• implements the abstract class / interface Layer
• contains an ogr object
• has a rasterize method, which returns a
  GeoRaster

32
Gtk2ExGeoComposite

• Three GeoRasters for colored images other than
  by color palettes

33
Exercise

• to be decided on lecture
• use some widget?
• implement better open vector data dialog box?
• implement an analysis tool?