Hillshade function calculation: ValueError: Received a NULL pointer

Question

I'm trying to get a raster from a DSM running the following code from python libraries osgeo-gdal in python qgis console:

import pandas as pd 
from osgeo import gdal

df = pd.read_csv(azimut_altitude.csv')
src_ds = gdal.Open(my_raster.tif')

#array generation function
def shade_array (index):
    out = r'.\my_path\raster'
    azimut = df.azimut[index]
    altitude = df.altitude[index]
    data = gdal.DEMProcessingOptions(options = [],
    colorFilename=None,
    format="GTiff",
    creationOptions=None,
    computeEdges=False,
    alg='Horn',
    band=1,
    zFactor=None,
    scale=None,
    azimuth=azimut,
    altitude=altitude,
    combined=False,
    multiDirectional = False,
    slopeFormat=None,
    trigonometric=False,
    zeroForFlat=False,
    addAlpha=None,
    callback=None,
    callback_data=None)

    shade = gdal.DEMProcessing(out + str(index), src_ds, 'hillshade')

    return shade

shade_array(0)

The problem is that when I run the script it yields this message:

ValueError: Received a NULL pointer. 

I've tried to solve introducing the input file as an array but then the error message is this:

TypeError: in method 'DEMProcessingInternal', argument 2 of type 'GDALDatasetShadow *'

Answer 1

The error message that you get indicates that there is something wrong with your input dataset. I think this is because there are formatting and syntax errors in your code. I have edited your script so that it should work:

import pandas as pd 
from osgeo import gdal
import os

df = pd.read_csv("azimut_altitude.csv")
src_ds = gdal.Open("my_raster.tif")

#array generation function
def shade_array (index):
    outdir = '/path/to/outdir' # i'm not sure if the path you provided is valid
    outfn = os.path.join(outdir, index + ".tif")
    azimut = df.azimut[index]
    altitude = df.altitude[index]

    # Most of the options that you have in your example are the defaults. 
    # These do not have to be set when you are satisfied with the defaults.
    # I have kept them here fow now, but feel free to remove anything that is 
    # not different from the default argument
    options = dict(
        colorFilename=None,
        format="GTiff",
        creationOptions=None,
        computeEdges=False,
        alg='Horn',
        band=1,
        zFactor=None,
        scale=None,
        azimuth=azimut,
        altitude=altitude,
        combined=False,
        multiDirectional = False,
        slopeFormat=None,
        trigonometric=False,
        zeroForFlat=False,
        addAlpha=None,
        callback=None,
        callback_data=None
    )

    # In your example you did not provide the options to the function. Below, it is done:
    ds = gdal.DEMProcessing(outfn, src_ds, 'hillshade', **options)

    # I have assumed that you would like to receive the actual data, 
    # not the file that is written on disk. 
    # You can easily modify this example if you want something else to be returned.
    data = ds.ReadAsArray()

    # close the dataset, by setting the ds to None.
    ds = None
    return data