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I would need some help with the Reclassify tool. I have written a script that produces rasters which I need to reclassify. My problem is, I want the values to be reclassified by standard deviation which I don't know how to do. I would like to make two new classes:

values < mean + 2 * standard deviation

values >= mean + 2 * standard deviation

I need help with putting this into a script.

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I'll give it a go.

Begin by loading your raster.

rast = arcpy.sa.Raster(pathtorasterfile)

Find the mean, standard deviations, minimum and maximum:

meanValue = rast.mean
std = rast.standardDeviation
minR = rast.minimum - .1 #just a little buffer room
maxR = rast.maximum + .1 #just a little buffer room

Setup the bounds:

target = meanValue + (2*std)

Create a remaprange object:

remapRangeValues = arcpy.sa.RemapRange([[minR,target-.00001,0],[target,maxR,1]])

Reclassify and save the new raster:

outReclass = arcpy.sa.Reclassify(rast, "VALUE", remapRangeValues)
outReclass.save(reclassifiedname)

I didn't test this, and I wasn't sure what you wanted to reclassify the values as. You may change the 0 or 1 in the RemapRange object to get the values you want.

Hope it helps.

  • Do you mean minR = rast.minimum - .1? – nmpeterson Apr 14 '16 at 19:11
  • Thank you! The problem with this is that RemapRange does not seem to take in variables, only actual values which I cannot hard code because I have a set of rasters and they all have different values. – danielaandrea Apr 14 '16 at 19:40
  • That's strange. I use it with variables in tools where I don't know what the values will be. Could you edit your question and post your existing code for troubleshooting? – dslamb Apr 14 '16 at 19:43
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Try something like this:

import arcpy

Set the workspace to the folder where you have your data

arcpy.env.workspace="Path:\to\your\data\"  
for raster in arcpy.ListRasters():

Create an object storing the st. dev. for the raster file:

    stdev_object=arcpy.GetRasterProperties_management(raster, "STD")

Store the numeric value of st. dev. in the variable stdev :

    stdev=stdev_object.getOutput[0]

Same thing for mean value:

    mean_object=arcpy.GetRasterProperties_management(raster, "MEAN")
    mean=mean.getOutput[0]
    threshold=mean + 2* stdev

You can use Raster Calculator for this instead of Reclassify:

    Output_raster="some\path\and\name\for\output\raster"
    expression="Con(" + raster + "<=" + str(threshold) + ",1,2"  

The string resulting from the above concatenation is an expression that tells Raster Calculator: if a raster cell value is <= than threshold change that value to 1, else change it to 2 (you can of course any values you like).

Now we actually reclassify the raster:

    arcpy.gp.RasterCalculator_sa(expression, Output_raster)

Done!

This works if you have your rasters in a ArcGIS native format, otherwise you need to convert them first. More info here: Get Raster Properties tool

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