##Accuracy Assessment
####Accuracy Assessment plugin for QGIS 2.0
by Jared Kibele
Graduate Student at Leigh Marine Lab, University of Auckland
This plugin calculates an error matrix from two raster datasets and outputs a CSV file that can be loaded into a spreadsheet (LibreOffice Calc, or MicroSloth Excel). To use it, open your raster layers in QGis, launch the plugin, select the layer you want to use as the reference layer, select your comparison layer, and select an output file with a .csv extension. Click 'OK' then open your .csv file with a spreadsheet. You should see something like this:
LayerName1 (ref) vs. LayerName2
1 2 3 4 Totals Accuracy
1 618 0 0 3 621 100
2 0 570 2 0 572 100
3 0 0 313 2 315 99
4 0 0 1 383 384 100
Totals 618 570 316 388 1892
Accuracy 100 100 99 99 100
Quantity Disagreement 5
Allocation Disagreement 3
The classes in this example are integers 1, 2, 3, 4. The reference layer is laid out in columns (so the reference class labels are headers in a row) and the comparison map data is laid out in rows (so the comparison class labels are in the first column). User's accuracy is in the 'Accuracy' column and producer's accuracy is in the 'Accuracy' row (see Congalton 1991 in references.txt). For a description of Quantity Disagreement and Allocation Disagreement, see Pointius and Millones 2011 (references.txt)
Current Limitations: This plugin assumes that raster values of 0 are unclassified so you can't use 0 as a class value. The plugin also assumes that you're providing it with two rasters that have the same pixel size and dimensions. I haven't tested it yet with different sized rasters. If it doesn't crash with different sized rasters, it will at least give you useless results. I intend to address that in future versions.
error_matrix.py can do other calculations that are currently not implemented in the GUI. error_matrix.py also has a bunch of explanitory comments that I won't include here. At some point I'd like to get the Sphinx documentation working with those comments but that will have to wait for a future version. error_matrix.py also has a bunch of doc tests. If you want to check that the code is working on your machine, go to the directory that contains error_matrix.py with the command line and type: "python error_matrix.py" and hit return. If you get output, please email it to me. If you just get another command prompt, that means the tests all passed.
This plugin was built with the "Plugin Builder" plugin by GeoApt LLC - geoapt.com. Thanks GeoApt.
-Jared