Quantum GIS Raster Array Module

A Python module for manipulating geographic raster image data in QGIS using numpy arrays. Includes a demonstration for Conway's Game of Life.

• View the Game of Life Blog Post
• View Example.txt for an example run.

Dependencies: QGIS 2.6.1 Brighton, Python 2.7

QGIS Python Console Setup

1. Go to the python command console in QGIS
   (Plugins > Python Console)

2. Enter in the console:
   import sys

3. Find the location path of this script
   C:\\User\\Desktop

4. Append it to the QGIS system paths with:
   sys.path.append(FILE_PATH_HERE)
sys.path.append ("C:\\User\\Desktop")

5. Import the Cells class for use in the console:
   from RasterArray import *

Cells

A. Creating the Cells Object

• Create a Cells object as a random array:

  cellsObject = Cells()

• Create a Cells object as a filled array:

  cellsObject = Cells(inRaster=n)

  • n is the value to fill the array with

• Create a Cells object as a custom array:

  cellsObject = Cells(inRaster=[(r1c1,r1c2,r1c3),(r2c1,r2c2,r2c3)])

  • r1c1..rncn refers to row 1 (r1) and column 1(c1) to row n (rn) and column n (cn)
  • The containers [] define a list and () define a tuple

• Create a Cells object with a raster file:

  cellsObject = Cells ("path_to_raster_file")

  • "path_to_raster_file" is the location of the raster with extension

B. Modifying and Obtaining Cell Values

• Modify a cell value:

  cellsObject.modify(x, y, value)

  • x and y are the coordinates of the cell to modify
  • value is the value to replace the cell value at the location
  • for non-geographic coordinates, use (x, y, value, geographic=False)

• Obtain a cell value:

  cellsObject.get(x, y)

  • x and y are coordinates of the cell to obtain
  • for non-geographic coordinates, use (x, y, value, geographic=False)

C. Output to Raster TIF

• Output a raster representing the changes:

  cellsObject.toRaster("path_to_output_raster_file")

  • "path_to_output_raster_file" is the location of the output raster file with extension

D. Additional Settings

• Set the band of the raster

  cellsObject = Cells (nband=n)

  • n is band number of the input raster, does not work for default

• Set the spatial reference system of the randomly generated raster

  cellsObject = Cells (EPSG=coorSys)

  • coorSys is the EPSG number of the spatial reference of the randomly generated raster

• Setting the dimensions and cell measurements of the randomly generated raster

  cellsObject = Cells (cols=c,rows=r,pixelWidth=w,pixelHeight)

  • c and r are inputs in whole numbers to specify the number of columns and rows
  • w and h are inputs in real numbers to specify the width and height of cells

GameofLife

A. Creating a GameofLife Object

• Create a GameofLife object:

  GoLObject = GameofLife()

B. Cycling the Game Board

• Cycle the game n times:

  GoLObject.cycle(n)

  • n is the number of times to cycle the gaming board

• Reset the game:

  x.reset()

  • reset the gaming board to the initial state

C. Additional Settings

C1. Data

• Set the initial board when creating the GameofLife object:

  GoLObject = GameofLife(raster="path_to_raster_file")

  • "path_to_raster_file" is the path to the raster file with extension to be used for the initial board

• Set whether or not to overwrite cycles:

  GoLObject.overwrite = boolean

  • boolean is set to True or False, where True overwrites each cycle, and False does not overwrite each cycle

• Set the spatial reference system of the randomly generated raster

  GoLObject = GameofLife(EPSG=coorSys)

  • coorSys is the EPSG number of the spatial reference of the randomly generated raster

C2. Aesthetics

• Set the style of the start and cycle boards with a qml file:

  GoLObject.qmlStyle = "path_to_qml_file"

  • "path_to_qml_file" is the path to the QGIS .qml style file used for changing the style of the output board

• Set the refresh speed:

  GoLObject.speed = x

  • x is the refresh speed in seconds before processing the next cycle

C3. Dimensions

• Set the width and height when creating the GameofLife object:

  GoLObject = GameofLife(width=w, height=h)

  • w and h are inputs in whole numbers to specify the width and height of the randomly generated board

• Set the raster cell sizes when creating the GameofLife object:

  GoLObject = GameofLife(cellWidth=w, cellHeight=h)

  • w and h are inputs in real numbers to specify the width and height of cells in the randomly generated board

Authors

• Richard Wen ([email protected])
• Dr. Claus Rinner ([email protected])