[GIS] Piping output of Iterate Raster tool into Raster Calculator tool using ModelBuilder

arcgis-10.1iteratormap-algebramodelbuilderraster-calculator

ArcGIS v10.1 ModelBuilder

Using ModelBuilder and map algebra, I want to compute a ten year average grid from a stack of 10. The problem is that only 1 grid (%raster%), the last one through the Iterate Rasters tool, is available as input to the Raster Calculator tool.

I am using the Iterate Rasters tool to go through a folder of asc grids. The folder contains ten subfolders, one for each year from 2001 to 2010, inclusive. Inside of each of these are twelve asc grids, one for each month. The monthly grids have identical names for all years where the number indicates the month (e.g., name07.asc). I am using a wildcard that works to successfully iterate over the grids (e.g., ten "July" grids), and define the projection for each; However, the raster calculator then only accepts one of these grids instead of all ten.

Is it possible to use the Iterate Rasters tool with the Raster Calculator tool in ModelBuilder?

Best Answer

If you try to output the iterate raster tool directly into raster calculator, you will only see the last iteration in the raster calculator layers and variables list. To get around this nuisance in model builder, use Collect Values to generate a list that you can pass off to Cell Statistics to do your calculations. Simply choose the "MEAN" overlay statistic and you will have your average grid calculations. You can always bring this average grid up in raster calculator if you need to make further calculations.

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Related Solutions

[GIS] Iterate through rasters in subfolders using Model Builder

When faced with a problem like this I use os.walk() which returns all files and then see if the files match what I want by extension, here's an example for shapefiles:

import sys, os, arcpy
InFolder = sys.argv[1]

for (path, dirs, files) in os.walk(InFolder):
    for ThisFile in files:
        fName,fExt = os.path.splitext(ThisFile)
        if fExt.upper() == ".SHP":
            fc = path + "\\" + ThisFile

Change fExt.upper() == ".SHP": to fExt.upper() == ".ASC": and then operate as normal with fc being the full path to the dataset.

The other option is to put all the rasters in manually... or semi manually:

Open a command prompt in your base folder and type:

DIR *.ASC /B/S

Which gives a list of all the ASCII files in all subfolders... if there's too many to select then try piping to a text file:

DIR *.ASC /B/S > ASC_File_List.txt
START NOTEPAD ASC_File_List.txt

Then select all, copy, and paste into the tool.

[GIS] How to use the math tool (“times”) in ArcGIS modelbuilder to multiply two raster sets while using an iterator

Since you have the Python tag, the following example is how you would accomplish this task using raster algebra in Python. Here I am assuming you have a variety of rasters in one GDB with a unique ID for each pair. The output is written to a separate folder in .tif format.

import arcpy, os
from arcpy.sa import *
arcpy.CheckOutExtension ("Spatial")

arcpy.env.workspace = r'C:\temp\temp.gdb'
inws  = arcpy.env.workspace
outws = r'C:\temp\out'

# List all of the "forestmask" rasters
rasters = arcpy.ListRasters("*forestmask*")

# 1) Assuming there is a "loss" counterpart with a unique ID
# 2) Loop through your raster list
for r in rasters:
    # Extract prefix and suffix for naming purposes later
    prefix = r.split("_")[0] + "_"  # Get just the prefix
    suffix = "_" + r.split("_")[2] + "_" + r.split("_")[3] # Get just the suffix

    # Define the "forestmask" and "loss" paths
    forestmask = os.path.join(inws, r)
    loss       = os.path.join(inws, r.replace("forestmask", "loss")) # Replace "forestmask" with "loss"

    # Convert these to raster objects
    r1 = Raster(forestmask)
    r2 = Raster(loss)

    # perform the raster algebra
    mycalc = r1 * r2

    # Save to disk (write to .tif)
    mycalc.save(os.path.join(outws, prefix + "deforestation" + suffix + ".tif"))

arcpy.CheckInExtension ("Spatial")

Best Answer

Related Solutions

[GIS] Iterate through rasters in subfolders using Model Builder

[GIS] How to use the math tool (“times”) in ArcGIS modelbuilder to multiply two raster sets while using an iterator

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