topic Re: raster extraction in Python Questions

raster extraction

InceptionWoznicki — Thu, 25 Feb 2016 22:21:47 GMT

I have a original tif file which has values from 2 to 28. From that original tif file, I am extracting cells having value >=10 using the following code. The code is working. However, when I open the new extracted tif file in GIS, I found that the cell values range from 10 30 instead of 10 to 28. I would really appreciate any help/ suggestion!

The code is provided below:

import arcpy, os

from arcpy import env

from arcpy.sa import *

#To overwrite output

arcpy.env.overwriteOutput = True

#Set environment settings

env.workspace = "C:/Subhasis/Highland/Project/Python_data"

outws="C:/Subhasis/Highland/Project/Python_data/HSA_10"

#checkout ArcGIS spatial analyst extension license

arcpy.CheckOutExtension("Spatial")

inraster = arcpy.ListRasters("*", "TIF")

for i in inraster:

flds = ("VALUE", "COUNT")

dct = {row[0]:row[1] for row in arcpy.da.SearchCursor(i, flds)}

sumcnt = sum(dct.values())

dct1 = {k:v for (k,v) in dct.items() if k >= 10}

sumcnt1 = sum(dct1.values())

percentage=(float(sumcnt1)/float(sumcnt))

print i,percentage

newraster = ExtractByAttributes(str(i), "VALUE>=10")

outname=os.path.join(outws,str(i))

newraster.save(outname)

Re: raster extraction

DarrenWiens2 — Thu, 25 Feb 2016 22:26:40 GMT

Is the 30 actually in the data, or just listed as the upper limit in the symbology?

Re: raster extraction

InceptionWoznicki — Fri, 26 Feb 2016 15:18:38 GMT

No, 30 is not in the data. The upper limit is 28.

Re: raster extraction

SteveLynch — Fri, 26 Feb 2016 15:59:39 GMT

for testing purposes I'd include (see highlighted 3 lines)

for i in inraster:

flds = ("VALUE", "COUNT")

dct = {row[0]:row[1] for row in arcpy.da.SearchCursor(i, flds)}

sumcnt = sum(dct.values())

dct1 = {k:v for (k,v) in dct.items() if k >= 10}

sumcnt1 = sum(dct1.values())

percentage=(float(sumcnt1)/float(sumcnt))

print i,percentage

arcpy.CalculateStatistics_management(str(i))

maxValue = arcpy.GetRasterProperties_management(str(i), "MAXIMUM")

print maxValue

newraster = ExtractByAttributes(str(i), "VALUE>=10")

outname=os.path.join(outws,str(i))

newraster.save(outname)

and the same for newraster