Save a GDAL dataset to Django file field

Question

I am processing a raster image inside my Django app. From a GeoTIFF file I am converting it to a COG. I am using gdal.Translate for the operation. I want to save the processed image without saving it locally. I want to use the GDAL dataset to read its bytes and be saved in a Django model's file field.

But suppose in this example, I am opening a dataset using gdal.Open. How can I save that to FileField?

from django.core.files.base import ContentFile
from django.db.models.fields.files import FileField
import osgeo
from osgeo import gdal

dataset = gdal.Open('/path/to/dataset.tif')
data_bytes = dataset.ReadAsArray().tobytes()

file_field = FileField()
file_field.save('dataset.tif', content_file, save=False)

model_instance = MyModel(file_field=file_field)
model_instance.save()

I am using GDAL 3.2.2.1 due to some constraints. Does function ReadAsArray not available in the version?

ModuleNotFoundError: No module named 'osgeo._gdal_array'

How can I do this correctly?

Answer 1

You can save the file to the expected destination with GDAL and just update the model.

With the storage attribute of the FileField you can get the expected path.

output_raster_name = "my_raster.tif"

# If you don't have an instance at this point just create a fake one
# my_model = MyModel()
my_model = MyModel.objects.get(pk=my_pk)

# This returns an absolute path taking into accound settings.MEDIA_ROOT
# and upload_to
output_raster = my_model.file_field.storage.path(name=output_raster_name)


dataset = gdal.Open("/path/to/dataset.tif")
warp = gdal.Warp(output_raster, dataset, dstSRS="EPSG:4326")
warp = None # Closes the files

If you are not using FileSysteStorage probably you can use more or less the same trick using GDAL Virtual File Systems, but i don't have experience doing it.

Also I think that gdal_array module should be present in your GDAL version so this shoud work:

from osgeo import gdal_array

# dataset_numpyarray = gdal_array.LoadFile("/path/to/dataset.tif")
# or

dataset = gdal.Open("/path/to/dataset.tif")
data_bytes = gdal_array.DatasetReadAsArray(dataset).tobytes()