Advanced Con Statement in Raster Calculations

Question

Hi there, i am trying to convert Python Code from 9.2 to 10.x The problem i am facing: in ArcGIS 9.2 it was possible, to create a Map Algebra Expression with a variable number of input rasters by defining it as a string Variable. In ArcGis 10 it is not anymore possible to use String Variables in a Raster Expression for building complex statements in a Con command. So if i have an input list with 4 values, i want to create the expression like this, (Raster(inRaster1) < var1[0]) & (Raster(inRaster2) > var1[1]) & (Raster(inRaster3) <> var1[2]) & (Raster(inRaster4) == var1[3]) , if i have only 2 input rasterfiles, only the first part of inRaster1 and inRaster2 should be used, if i have 16 or more files it should also work. A conversion from String to Raster would be maybe the best solution, but the Con Command doesn't accept this. Any suggestions, how to deal in ArcGis 10 with a variable number of input rasters? With best regards

PhilMorefield · Answer

It took some getting used to, but the new map algebra can make things pretty clean. My two cents (with Python style guide enforced!):
import arcpy as ap
from arcpy import sa

ap.CheckOutExtention('Spatial')
ap.env.overWriteOutput = True

raster1 = ap.Raster("D:\ACC\version01_lc2.img")
outraster4 = "D:\ACC\version01_lc_res04.img"

var1 = [311, 401]
var2 = 23
var3 = 27

tempRas = sa.Con(raster1 < var1[0] | raster1 > var1[1], var2, var3)
tempRas.save(outraster4)

curtvprice · Answer

IMHO, using substitution syntax makes for more readable code, whether you're using the old or new tools. Note the %s substitution converts numbers to strings for you if that is required. expression = "(Raster(%s) < %s) & (Raster(%s) > %s) & " "(Raster(%s) <> %s) & (Raster(%s) == %s)" expression = expression % \ (inRaster1,var1[0],inRaster2,var1[1],inRaster3,var1[2],inraster4,var1[3]) NewRaster=eval(expression). NewRaster.save("outRaster")

franzsuppan · Answer

Thanks a lot Chris and Luke for your quick and perfect response!!!

I tried the eval Function (to be honest - i never used it before - and it works!!!)
Below is a working sample code:

import arcpy
import sys, string, os, time, math
from arcpy.sa import *

arcpy.CheckOutExtension("Spatial")
arcpy.env.overwriteOutput = True

raster1 = "D:/ACC/version01_lc2.img"
outraster4 = "D:/ACC/version01_lc_res04.img"

# suppose 
var1 = [311, 401]
var2 = 23
var3 = 27

exp04 = "Con((Raster(raster1) < var1[0]) | (Raster(raster1) > var1[1]), var2, var3)"
res04 = eval(exp04)
res04.save(outraster4)