Creating a quality raster map in QGIS?

Question

I've got 2 raster maps (both with the same values: 0-100). After calculating the average I need to know how precise the map is. Is there any tool in QGis?

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I try to explain my problem in another way:

I have 2 or maybe 3 percentaged raster maps. After putting together ((a+b+c)/3) I need to get a map that shows if the result map is statistically firm.

For instance: If all 3 maps have the same value in an area the result must be reliable/firm. If 2 maps have the same values and 1 map is totally different the result is a little bit unreliable. If 3 maps are totally different the result is unreliable.

I want to create a colored map (green, orange, red). I already have processed the average map!

Answer 1

You can do this using QGIS' Raster calculator. Using 1.8.0:

• Add your two layers.
• Zoom to their extent.
• Navigate to: Raster -> Raster Calculator
• Enter your expression. So it will be something like: round((LayerA@1 + Layerb@1) / 2)
• Go to the layer properties for the new layer. Set colour map to "Pseudocolor" or play around to set actual desired colours.

Note: The "round" isn't strictly necessary. It just means your output will be integers rather than floats.