[QGIS-Developer] PYQGIS - Numpy array to QgsRasterLayer without writing to file first

[Eric Younkin - NOAA Federal]

Hi Benjamin,

This does appear to work, I am now able to use vsimem file handlers with
gdal rasters to go from numpy arrays to qgis raster layers effectively.
Very exciting, thanks for this tip!  I had another QGIS dev question, but I
will start a new thread for that.

For anyone else, this is all that I did:

dataset = gdal_driver.Create('/vsimem/imagetst.tif', cols, rows, no_bands,
gdal.GDT_Float32, creation_options)
...write array to band, set geotransform, etc....

rlayer = QgsRasterLayer('/vsimem/imagetst.tif', 'imagetst', 'gdal')

Thanks again,
Eric

On Wed, Mar 3, 2021 at 12:57 AM Benjamin Jakimow <
benjamin.jakimow at geo.hu-berlin.de> wrote:

> Hi Eric,
>
> you might try to use a /vsimem/ path. For example, save your image to
> "/vsimem/myimage.tif" and
> open it as QgsRasterLayer. I haven't tested it with gdal.Datasets, but it
> works with with ogr.DataSources.
> Probably you shouldn't overwrite or delete the "/vsimem" object while QGIS
> has still a reference on it.
>
> More details here:
> https://gdal.org/user/virtual_file_systems.html#vsimem-in-memory-files
>
> Greetings,
>
> Benjamin
>
> On 2021-03-03 00:00, Eric Younkin - NOAA Federal wrote:
>
> Hello,
>
> I've been trying to figure out how to draw grids and lines from numpy
> arrays without driving to a raster/vector file first.  I tried using the
> gdal 'MEM' driver to make a gdal Dataset from a numpy array and pass that
> in as a QgsRasterLayer, I get the following:
>
> >>> memobj
> <osgeo.gdal.Dataset; proxy of <Swig Object of type 'GDALDatasetShadow *'
> at 0x0000019B3131AC30> >
> >>> QgsRasterLayer(memobj, 'testlayer', 'gdal')
> Traceback (most recent call last):
>   File "<input>", line 1, in <module>
> TypeError: QgsRasterLayer(): arguments did not match any overloaded call:
>   overload 1: too many arguments
>   overload 2: argument 1 has unexpected type 'Dataset'
>
> The only other approach that I could find was:
>
>
> https://gis.stackexchange.com/questions/201804/how-to-create-raster-layer-directly-from-numpy-array-in-qgis-without-saving-to
>
> but I suspect that the return from the processing.run command is probably
> a temp file, so it is still going to file.  Is there not a way to generate
> a raster layer from a numpy array without writing to file first?
>
> Thanks,
> Eric
>
> --
> Eric Younkin
> Physical Scientist
> NOAA OCS, Hydrographic Systems and Technology Branch
> 1315 East-West Highway
> N/CS11, Room 6604
> Silver Spring, MD 20910
> Office: 240-847-8208
> Cell: 828-331-8197
>
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>
> --
> --
> Benjamin Jakimow, Doctoral Researcher
> Earth Observation Lab | Geography Department | Humboldt-Universität zu
> Berlin
>
> e-mail: benjamin.jakimow at geo.hu-berlin.de
>
> phone:  +49 (0) 30 2093 6894
> mobile: +49 (0) 157 5656 8477
> fax:    +49 (0) 30 2093 6848
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> room: 2'222
>


-- 
Eric Younkin
Physical Scientist
NOAA OCS, Hydrographic Systems and Technology Branch
1315 East-West Highway
N/CS11, Room 6604
Silver Spring, MD 20910
Office: 240-847-8208
Cell: 828-331-8197
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