/qgis-rasterarray

Raster data example in QGIS using numpy arrays

Primary LanguagePythonMIT LicenseMIT

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.

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