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I have two set of rasters, with data that should correlate...one are measured data, one are modelled data. The correlation is weak, however, when looked at with a normal regression analysis. I suspect that different parts of the base terrain need different modelling input, or that in some parts there is a shift between the correlating cells.

So now I try to visualize where these residuals are highest between my two rasters, and where the real outliers are and whether they are in similar terrain.

Is there any tool that would allow me to directly compare the rasters in GIS?

I run ArcGIS Desktop 9.3 with Spatial Analyst and Statistics, and also have QGIS and GRASS on my Linux-based machine.

What would be easiest?

I am not trying to do a full-on analysis, I am just trying to see where the odd data are and if there is a systematic spatial pattern behind them.

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Maybe a simple raster difference (raster1 minus raster2) will give you a starting point.

I would use ArcGIS Desktop for that, but simply because I know how to do it in ArcGIS Desktop and don't know how in QGIS.

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