topic Re: NDVI calculation using python: Extracting Bands in Python Questions

NDVI calculation using python: Extracting Bands

Yaseen_TahaMustafa — Sat, 11 Dec 2021 15:28:38 GMT

Dear All,
I am trying to calculate NDVI for a list of Landsat images. First i identified the path of the input images and the output results as well. Then I created a loop to read each input raster and trying to extract band 4 and 5 from the raster then calculate the NDVI and finally save the NDVI result of landsat image.
However, I might be doing something not acceptable in extracting bands, and I did search online how to extract a band from an image in python but I could not fixed.
Any help would be highly appreicated. The script is shown below along with the error.

import os, arcpy, string
from arcpy.sa import *
from arcpy import env


arcpy.CheckOutExtension("Spatial")

arcpy.env.workspace =r"E:\test\Landsat"
out_workspace =r"E:\test\Results"

# Get a list of grids in the workspace.
rasters = arcpy.ListRasters("","TIF")

for raster in rasters:

    # Set the outputname for each output to be the same as the input.
    output_path = os.path.join(out_workspace,raster)

    #create raster object
    raster_path = os.path.join(arcpy.env.workspace,raster)
    raster_object = arcpy.Raster(raster_path)

    inRaster = (raster_object)
    red = arcpy.sa.Raster(inRaster+'\Band_4')
    NIR = arcpy.sa.Raster(inRaster+'\Band_5')
    # NDVI Calculation
    num = arcpy.sa.Float(NIR-red)
    denom = arcpy.sa.Foat(NIR+red)
    NDVI = arcpy.sa.Divide(num, denom)
    #save it
    #con_raster.save(output_path)
    NDVI.Save(output_path)
    arcpy.CheckInExtension("Spatial")‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

The errors are:

Traceback (most recent call last):
  File "E:\test\NDVI20200404.py", line 24, in <module>
    red = arcpy.sa.Raster(inRaster+'\Band_4')
  File "C:\Program Files (x86)\ArcGIS\Desktop10.7\ArcPy\arcpy\sa\Functions.py", line 4409, in Plus
    in_raster_or_constant2)
  File "C:\Program Files (x86)\ArcGIS\Desktop10.7\ArcPy\arcpy\sa\Utils.py", line 53, in swapper
    result = wrapper(*args, **kwargs)
  File "C:\Program Files (x86)\ArcGIS\Desktop10.7\ArcPy\arcpy\sa\Functions.py", line 4406, in Wrapper
    ["Plus", in_raster_or_constant1, in_raster_or_constant2])
RuntimeError: ERROR 000732: Input Raster: Dataset \Band_4 does not exist or is not supported‍‍‍‍‍‍‍‍‍‍

Re: NDVI calculation using python: Extracting Bands

DanPatterson_Retired — Wed, 08 Apr 2020 07:29:26 GMT

First, check the raster properties to see if the raster does have bands 4 and 5.

Second, why don't you use...

NDVI—Spatial Analyst module | Documentation

Re: NDVI calculation using python: Extracting Bands

Yaseen_TahaMustafa — Wed, 08 Apr 2020 07:46:30 GMT

Hi Dan,

Thanks for the quick response. I have found a script that fits my request. It is shown here:

python - How do i extract 3 bands out of a 4 band image using NumpyArrayToRaster()? - Stack Overflow

Re: NDVI calculation using python: Extracting Bands

DanPatterson_Retired — Wed, 08 Apr 2020 07:59:48 GMT

probably because you bands aren't named as in that example

'\Band_4' will therefore fail.
Since you already have the spatial analyst extension there is no advantage to using numpy and unless you know how to account for nodata values which may exist, then your results may be suspect. I have several blog posts on using numpy with raster data which you might want to look at if you want to persist on using a non-SA solution

Re: NDVI calculation using python: Extracting Bands

Yaseen_TahaMustafa — Wed, 08 Apr 2020 09:39:31 GMT

Hi Dan,

Yes sure ... it be very kind of you to share your blog posts with me.

Regards

Yaseen