How to make a new raster using con() script in Python?

Question

I'm new to Python and have been trying to code a raster calculator style script. Basically, I want to convert a raster that has values 0 to -10,000 into a raster that is populated by 1s between certain values.

The reason I want to do it in Python is because I eventually want to automate this process so that I can pick out different values (ie 0 to -10, -5 to -25 etc) and end up with a raster of 1s for each. My aim then is to convert these to polygons so that I can then do a number of vector clip operations across about 800 shapefiles.

I've written a script which produces a new raster at the end but instead of this grid being full of 1s it has values 0-256, so somewhere in my code there's a bug. I'd be grateful if anyone can spot it! If anyone has a way to speed up the code or a better idea for how I can do all this also then that would also be interesting to know.

Here's my code:

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

arcpy.env.overwriteOutput = 1 #this also doesn't work by the way, I have also tried            
#TRUE, no errors come up but it still doesn't let me overwrite the output file

#Set environment settings
env.workspace = "C:/folderlocation where inRaster is stored"

# Set local variables
inRaster = Raster("inputraster")

# Check out Spatial Analyst extension license
arcpy.CheckOutExtension("Spatial")

# depths wanted from inputraster raster
var = [-2500,-3000] #min depth, max depth

#Execute and save Con
OutRaster = Con((inRaster <= var[0])&(inRaster <= var[1]),1)

OutRaster.save("C:/drivelocation/outputfilename")

If anyone has any ideas they'd be gratefully received! Many thanks.

Answer 1

I think the problem is with this expression

OutRaster = Con((inRaster <= var[0])&(inRaster <= var[1]),1)

Con expects the following format

Con (in_conditional_raster, in_true_raster_or_constant, {in_false_raster_or_constant}, {where_clause})

Which in your case

Con((inRaster <= var[0])&(inRaster <= var[1]),1)

can be broken down into

• in_conditional_raster, (inRaster <= var[0])&(inRaster <= var[1])

• in_true_raster_or_constant, 1

I'm a bit confused as to what you're trying to do. You seem to want to turn into 1 the values that fit both of the following criteria

• inRaster <= -2500
• inRaster <= -3000

Those two expressions can be reduced to inRaster <= -3000.

So all pixels that have values less then or equal to -3000 have been turned to 1. The rest are left as is. At least that's what your code says. No way of knowing for sure though unless you post the attribute table of this raster or the actual raster file itself.

I think you meant (inRaster <= var[0])&(inRaster > var[1]). That way you'd catch values between -2500 and -3000.

Btw, what is the range of values in the original raster?