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Conditional statements Raster Calculator

Question asked by tronderenergi on Sep 16, 2020
Latest reply on Sep 16, 2020 by jjohnson_washoe



I am working on a weighted analysis with four rasters. Two of the rasters have areas of NoData, which means I do not want to use the Weighted Overlay tool because this tool does not ignore NoData in calculations. If I were to use the Weighted Overlay tool I would have to assign a value to areas of NoData - and my conclusion is that this would not make the weight calculations completely correct. Someone please correct me if I am wrong!


To get around this problem I started looking into using conditional statements using Con in Raster Calculator. I found a post where someone came up with this syntax:


Con(IsNull(Raster3), Float(w1*Raster1 + w2*Raster2)/(w1+w2) , Float(Raster1 + Raster2 + Raster3)/3)

Where wx is the weighting applied to each raster.


So this works fine with three rasters, where one of the rasters contains areas of NoData.

But what is the syntax if you have two rasters that contains areas of NoData?


Additional questions:
- Is the division necessary in the calculations because not all three rasters are included? And why is the second Float divided by the number 3 and not 1 (as in 100%)?

- In the syntax above, in the second Float the rasters are not multiplied with weightings - is this correct? And if so, please explain why.



Hoping for help!!