[gdal-dev] Merge and Overviews with VSIMEM

[Brenton Mallen]

Hi,

I'm attempting to merge 2 multi-band tiffs as well as build overviews for
the resulting merged tiff.  I'm a bit confused when I attempt to use a
`vsimem` object to perform the actions in memory.  For example, I have a
couple of functions defined as

def merge_bands(tiffs, out_file):
    """Merge multi-band GeoTIFFs together.

    Args:
        tiffs (list): List of paths to TIFFs to be merged
        out_file (str): Path to output file
    """
    merge_command = 'gdal_merge.py -separate -o {} '.format(out_file)
    merge_command += ' --config GDAL_CACHEMAX 256'
    merge_command += ' -co compress=LZW'
    merge_command += ' -co TILED=YES'
    for tiff in tiffs:
        merge_command = merge_command + ' {}'.format(tiff)
    sp.check_call(merge_command, shell=True, stdout=sp.PIPE, stderr=sp.PIPE)

def build_overviews(filename, levels):
    """Build overviews.
    Args:
        filename (str): Input filename
        levels (list): Level (int) or list or levels (ints)
            to build overviews for.
    """
    if not isinstance(levels, list):
        levels = [levels]
    command = 'gdaladdo'
    command += ' -r average'
    command += ' {}'.format(filename)
    command += ' {}'.format(' '.join(str(x) for x in levels))
    sp.check_call(command, shell=True, stdout=sp.PIPE, stderr=sp.PIPE)


When I attempt to call it, using the following, the `vsimem` object seems
to no longer be accessible to perform the overview creation:

merged_mem = '/vsimem/merged.tiff'

merge_bands(['file1.tiff', 'file2.tiff'], merged_mem)
build_overviews(merged_mem, [2,4,8,16,32,64])

I get an `exit status 2` which I believe is due to `merged_mem` being a
NoneType after the merge is performed.

I'm also confused about best practices.  Ideally, I'd like to do this all
in the python wrapper but there doesn't seem to be an immediately obvious
parallel for the `gdal_merge` script.

I'm using python 3.8 and GDAL 3.0.2.

Any guidance would be appreciated and thank you for your time,
Brenton

-- 
Brenton Mallen
(561) 376-6580 | Site <https://brentonmallen.com/> | GitHub
<https://github.com/brentonmallen1> | LinkedIn
<https://www.linkedin.com/in/brentonmallen/>
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