Hi Umberto,
There isn't information in your question about the size of the raster
image, but as you are reading it in chunks, it probably is large. Hence
my guess is that your in-memory raster is not big enough to hold the
data, without giving an error message. And the subsequent gdal.Warp
simply cannot handle this.
If the file-raster weren't large, you could simply load it into memory
in one command.
Armin
On 21/02/2020 16:52, umbertofilippo wrote:
Sorry if this is a copy of a question I already asked on
gis.stackexchange (
here
<https://gis.stackexchange.com/questions/351577/cannot-use-in-memory-raster-object-with-gdal-warp-gdal-python-api>
), but I thought I might get more chance to receive an answer here.
These are the operations I am doing in my code:
1 - reading an existing raster (tif)
2 - creating a in memory raster object
3 - reading the existing raster object in chunk as array
4 - making some calculations
5 - writing the array to my in memory object
What I want to do now is, with the in memory raster object ready to be
used,
feed it to gdal warp, which should also output an intermediate raster
object
that I'll be use afterwards.
However, when I try to GetRasterBand() out of this latter raster object, I
receive an error because it is actually equal to None:
AttributeError: 'NoneType' object has no attribute 'GetRasterBand'
I am pretty sure it is about saving/updating/flushing the status of the
raster object after the calculations but I could not find out if this
is the
actual problem.
How can I use in memory (intermediate) files in my script?
Here is the code code I am using (the error is at the very last line):
from osgeo import gdal, gdalconst
import numpy as np
in_raster = gdal.Open(r'/my/raster.tif', gdalconst.GA_ReadOnly)
in_b = in_r.GetRasterBand(1)
b1 = in_raster.GetRasterBand(1)
xsize = b1.XSize
ysize = b1.YSize
step = 10 # THIS IS THE CHUNK SIZE!
ystep = ysize / step
ystep = int(ystep)
yresidual = ysize - (ystep * step)
driver = gdal.GetDriverByName("MEM")
temp_calc = driver.Create('',
xsize,
ysize,
1,
gdal.GDT_Float32)
temp_b = temp_calc.GetRasterBand(1)
for i in range(step):
if i != step-1:
arr_part = in_b.ReadAsArray(
0, ystep * i, xsize, ystep).astype('float32')
data = np.nan_to_num(arr_part)
temp_b.WriteArray(data, 0, ystep * i)
else:
arr_part = in_b.ReadAsArray(
0, ystep * i, xsize, ystep + yresidual).astype('float32')
# replace nan with zeros
#
https://docs.scipy.org/doc/numpy/reference/generated/numpy.nan_to_num.html
data = np.nan_to_num(arr_part)
# write array chunk to (in memory) file
# https://gdal.org/python/osgeo.gdal.Band-class.html#WriteArray
temp_b.WriteArray(data, 0, ystep * i)
# get raster resolution
in_gt = in_raster.GetGeoTransform()
in_x = in_gt[1]
in_y = -in_gt[5]
kwargs = {'xRes': in_x,
'yRes': in_y,
'targetAlignedPixels': True,
'resampleAlg': 'average',
'format': 'MEM'
}
ds = gdal.Warp('',
temp_calc,
**kwargs)
b1 = ds.GetRasterBand(1)
# ds is None and the above line throws the exception
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Dr Armin Schmidt
Dipl.-Phys., Dr. rer. nat.
GeodataWIZ: Geo Data + Visualisation
www.GeodataWIZ.com
www.GeodataWIZ.com/armin-schmidt
Honorary Secretary ISAP
International Society for Archaeological Prospection
www.archprospection.org
Honorary Visiting Research Fellow, University of Bradford
School of Archaeological and Forensic Sciences
Honorary Fellow, Durham University
Department of Archaeology
http://orcid.org/0000-0002-4241-5381
Email: [email protected]
Available in print:
Guidelines for the use of Geophysics in Archaeology (2015). Namur: EAC.
Earth Resistance for Archaeologists (2013). Lanham: AltaMira Press
Geophysical Data in Archaeology (2013). Oxford: Oxbow Books.
http://www.amazon.co.uk/-/e/B0034QC4OW
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