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I am trying to manipulate bad pixel values in a raster by using the Con-Statement via ArcPy. Using the build-in Map Algebra function "Raster Calculator", the results are good. To transfer the work flow to a script, the outcome is different. The pixel values should be between [-1;1].

arcpy.env.workspace = out_folder #path to my folder containing the raster files
list = arcpy.ListFiles('*.tif')
for ras in list:
     outras1 = Con(ras > 1, 1, ras)
     outras2 = Con(outras1 < -1, -1, outras1)
     outras2.save(ras + '_mod.tif')

Can you tell, what I am doing wrong?

The results show only pixel values of 1. Additional information: I have large areas of NoData values in my raster.

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  • Otherwise, the combination of the Con statement: outras1 = Con(ras > 1, 1, Con(ras < -1.0,-1.0, ras)) produces the same result.
    – Andi90
    Commented Nov 9, 2017 at 13:26
  • 1
    Try r=arcpy.Raster(ras), because this will create raster from string.
    – FelixIP
    Commented Nov 9, 2017 at 19:06
  • Thankyou for the "object" reference to this process. I am converting pixels with multiple elevation values to the maximum elevation found for hundreds of polygon segments that cross over culverts. Sample code. rasterlist = arcpy.ListRasters(raspref+"*") print "rasterlist= ",rasterlist for i in rasterlist: inputraster = i print "inputraster = ",inputraster print "Getting MAXIMUM elevation value in DEM" raster = arcpy.GetRasterProperties_management (inputraster, "MAXIMUM") elevMax = float(raster.getOutput(0)) print "MAXIMUM elevation for", inputraster, "= ", elevMax rast = arcpy.Raster(inputrast
    – MRichey
    Commented Nov 21, 2017 at 18:28
  • This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review
    – Dan C
    Commented Dec 12, 2017 at 17:24

1 Answer 1

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@FelixIP comment is correct, you need to convert your raster file to a raster object using arcpy.Raster() before using Con().

Here is the code that worked for me:

import arcpy
from arcpy.sa import *
from arcpy import env

env.workspace = r"F:\Test\Test\FolderName"

ext_out = arcpy.CheckOutExtension("SPATIAL")

raslist = arcpy.ListRasters('*.tif')

for ras in raslist:
    raster = arcpy.Raster(ras)

    ras_con = Con(raster < -1, -1, Con(raster > 1, 1,raster))
    ras_con.save(ras[:-4]+"_Final.tif")
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  • 1
    This post is way more informative than any of the official Esri documentation I've read on using the raster calculator in Python. Thank you!
    – Stephen Lead
    Commented Oct 18, 2022 at 22:44

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