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To calculate the STI one applies the following formula in the raster calculator: Power(“FlowAccumulationArea_Raster”/22.13,0.6) * Power(Sin(“Slope_Raster”/0.0896),1.3)

Now I have a problem which I don't understand. When I apply the formula in the raster calculator, the resulting raster shows randomly pixels with no data, while other pixels have been calculated correctly. My slope and flowaccumulation rasters are consistend and give values for each cell. In my opinion the raster calculator shouldn't pretend that for some of the cells the equation has no solution; which it does by stating "no data". Anybody has an idea what might be the cause?

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  • "In my opinion the raster calculator shouldn't pretend that for some of the cells the equation has no solution; which it does by stating "no data". What should it do? Have you checked the results messages?
    – If you do not know- just GIS
    Aug 20, 2016 at 2:18

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Convert your slope which is most likely in degrees into radians and repeat your calculations.

Your results show that you are trying to get Power(s,1.3) with s being negative

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