Le 11/05/2025 à 00:20, Michael Sumner via gdal-dev a écrit :
Hello, I have a question about safely re-casting a dataset to another,
I want to use Multidim to re-orient an MDArray as a classic 2D raster.
I was a bit surprised that this works (I just overwrite poSrcDS with
the classic form):
I'm passing in 'osFilename', 'osArrayName' and two dimension indexes
'index_x' and 'index_y', the first "Open()" line is a literal copy
from vrtdataset.cpp:
// I've removed all the nullptr checks from this code
auto poSrcDS = std::unique_ptr<GDALDataset, GDALDatasetUniquePtrReleaser>(
GDALDataset::Open(osFilename, GDAL_OF_RASTER |
GDAL_OF_VERBOSE_ERROR,
aosAllowedDrivers.List(), aosOpenOptions.List(),
nullptr));
// now open in mdim mode, and get the specified MDArray in Classic
form with index_x,index_y
auto poMDimDS =
std::unique_ptr<GDALDataset>(GDALDataset::Open(osFilename,
GDAL_OF_MULTIDIM_RASTER));
auto poMdimGroup = poMDimDS->GetRootGroup();
auto poArrayDS = poMdimGroup->OpenMDArrayFromFullname(osFilename);
auto poClassicDS = poArrayDS->AsClassicDataset(index_x, index_y);
// FIXME how to safely swap poSrcDS with poClassicDS
poSrcDS = std::unique_ptr<GDALDataset,
GDALDatasetUniquePtrReleaser>(poClassicDS);
My question is about the last line where poClassic "replaces" poSrcDS:
what am I responsible for to make that safe?
That's perfectly fine. In the mdim API, objects returned by
GetRootGroup(), OpenMDArray(), AsClassicDataset(), etc. , keep the
necessary parent objects alive through shared_ptr mechanism. Furthermore
in your example, there is no relationship between poSrcDS et
poClassicDS, so even if that wasn't the case, your final assignment
would be still safe.
--
http://www.spatialys.com
My software is free, but my time generally not.
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