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I have a workspace with NDVI rasters and another workspace with greyscale rasters. The rasters have the same name.

I want to reclassify the NDVI raster while also using the greyscale values in a function. Depending on the greyscale value, another reclass function should be used. So for every pixel, the correct function has to be found.

I need to use an if statement: if the greyscale raster cell value is high, another statement should be used but the code results in an error:

Invalid use of raster with Boolean operator or function. Check the use of parentheses where applicable.

arcpy.env.workspace = ndviws
ndvirasterlist = arcpy.ListRasters()

for rimage in ndvirasterlist:
    ndvi_raster = arcpy.sa.Raster(rimage)
    grey_raster = arcpy.sa.Raster(os.path.join(greyvalues,rimage))
    if grey_raster <= 28523:
        output_raster = Con(ndvi_raster < -0.0000006 * grey_raster +  0.3448,2,1)
    if grey_raster >28523 and grey_raster < 50000:
        output_raster = Con(ndvi_raster < -0.000009 * grey_raster + 0.437673,2,1)
    if grey_raster >=50000:
        output_raster = Con(ndvi_raster < -0.000007 * grey_raster + 0.5233,2,1)
    output_raster.save(os.path.join(outputws,rimage))

edit: **edited so that there are now 3 if statements. Is this still working with con method?

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    You have "values" misspelled in arcpy.sa.Raster(os.path.join(greyvaluews,rimage)). That could be a source of an error unless the variable name is similarly misspelled earlier in the program.
    – P.T. Curran
    Commented Sep 9, 2019 at 11:38
  • thank you PT. that was just a typing mistake since I couldnt copy paste the code here. Would you know how I can do that with 3 IF statements (not 2)?
    – GIS7
    Commented Sep 9, 2019 at 12:08
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    I'm afraid I don't; my experience with rasters is a bit scattershot. I know I've encountered errors because I've misspelled variables before, so I thought that might help.
    – P.T. Curran
    Commented Sep 10, 2019 at 13:06

1 Answer 1

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if grey_raster <= 28523 does not make sense to arcpy. 28523 is the value you want to check against each pixel of grey_raster, which is where Con function comes handy.

In your case, you should use nested conditions like:

arcpy.env.workspace = ndviws
ndvirasterlist = arcpy.ListRasters()

for rimage in ndvirasterlist:
    ndvi_raster = arcpy.sa.Raster(rimage)
    grey_raster = arcpy.sa.Raster(os.path.join(greyvaluews,rimage))
    output_raster = Con(grey_raster <= 28523, Con(ndvi_raster < -0.0000006 * grey_raster +  0.3448,2,1), Con(ndvi_raster < -0.000009 * grey_raster + 0.437673,2,1))
    output_raster.save(os.path.join(outputws,rimage))

EDIT

If you have more than two conditions to check against, you can simply produce intermediate rasters, and work on them as you go (not tested):

arcpy.env.workspace = ndviws
ndvirasterlist = arcpy.ListRasters()

for rimage in ndvirasterlist:
    ndvi_raster = arcpy.sa.Raster(rimage)
    grey_raster = arcpy.sa.Raster(os.path.join(greyvaluews,rimage))
    # first condition (grey_raster <= 28523)
    output_raster = Con(grey_raster <= 28523, Con(ndvi_raster < -0.0000006 * grey_raster +  0.3448,2,1), 1)
    # second condition (grey_raster >28523 and grey_raster < 50000)
    output_raster = Con((grey_raster > 28523) & (grey_raster < 50000), Con(ndvi_raster < -0.000009 * grey_raster + 0.437673,2,1), output_raster)
    # third condition (grey_raster >=50000)
    output_raster = Con(grey_raster >= 50000, Con(ndvi_raster < -0.000007 * grey_raster + 0.5233,2,1), output_raster)
    output_raster.save(os.path.join(outputws,rimage))
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  • thank you @umbe1987. In my real case I have 3 if statements, not just 2 (above was just an example). I guess I can't use the con method then? Which alternative would you suggest?
    – GIS7
    Commented Sep 9, 2019 at 9:23
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    Not sure if it will work, but I provided another possible solution. Feel free to test it and report back your results if you want.
    – umbe1987
    Commented Sep 9, 2019 at 14:08
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    your edit worked when i changed "output_raster>28523" to "grey_raster>28523" in the second and "output_raster >=50000" to "grey_raster >=50000" in the third condition. Also at the very end of condition 2 and 3 I had to change the value 1 to the variable "output_raster", since the values were overwritten before. Thank you very much.
    – GIS7
    Commented Sep 10, 2019 at 11:53
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    Glad it helped. I changed the code according to your comments so that it will be correct.
    – umbe1987
    Commented Sep 10, 2019 at 12:21

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