[Qgis-user] Importing a raster into a Geopackage

[Fernando M. Roxo da Motta]

On Wed, 2 Dec 2020 18:52:31 -0500, Nicolas Cadieux
<njacadieux.gitlab at gmail.com> wrote:

  I just find out a "hint" I have in my "hints" directory with the
following content:

===============8<----- tif_to_Geopackage ---------

http://www.qfield.org/docs/project-management/dataformat.html

Use GeoPackage

We recommend to us the geopackage format to deal with raster data. The
following commands will convert a file called raster.tif to a file
raster.gpkg with pyramids. Make sure you adjust EPSG:21781 (CH1903
LV03) to your desired CRS.

gdal_translate --config OGR_SQLITE_SYNCHRONOUS OFF -co
APPEND_SUBDATASET=YES -co TILE_FORMAT=PNG_JPEG -a_srs EPSG:21781 -of
GPKG raster.tif raster.gpkg gdaladdo --config OGR_SQLITE_SYNCHRONOUS
OFF -r AVERAGE raster.gpkg 2 4 8 16 32 64 128 256

===============8<----- tif_to_Geopackage ---------


  HTH


> Hi,
> Just to close this thread, this is the answer I got from Even Rouault
> on the gdal dev mailing list.
> 
> 
> > On mercredi 2 décembre 2020 15:16:44 CET Nicolas Cadieux wrote:
> > Hi,
> > 
> > This follows a discussion in the qgis-user mailing list.  We are
> > using gdal_translate (and QGIS "export as") on a 8bit unsigned
> > single band tiff to a .gpkg.  When using no -ot switch or when
> > using -ot Byte, this results in a 4 band .gpkg raster with the
> > wrong values.  (Values in band 1 to 3 are similar but off the
> > mark). Band 4 is set at 255 as expected. Looks like some type of
> > compression is going on in the band 1 to 3).
> > 
> > When saving using the -ot Int16 or Float32 switch, all is well and
> > the result has one band with the correct values.
> > 
> > ex: gdal_translate -ot Int16 -of GPKG "E:/Users/Nicolas/Google Drive
> > Nicolas/Partage_temporaire/qgis/int16.gpkg" "E:/Users/Nicolas/Google
> > Drive Nicolas/Partage_temporaire/qgis/int16.gpkg"
> > 
> > Is this a possible problem with the driver or is the problem
> > sitting 18 inches in front of the screen? Problem similar on a Mac
> > running QGIS 3.10.1-A with GDAL 3.0.2 and QGIS3.16 on Windows
> > running GDAL 3.1.4.
> > 
> > Test files are found here:
> > https://drive.google.com/drive/folders/1fMl9odowUFFRQFK61rTxgHeom_D8ymN6?usp
> > =sharing
> >   
> 
> The answer is there:
> https://gdal.org/drivers/raster/gpkg.html#tile-formats
> 
> For Byte input (that isn't recognized as to be used by the tiled
> gridded coverage data), the default tile format will use JPEG lossy
> compression for tiles with a fully opaque channel.
> 
> -co TILE_FORMAT=PNG will use lossless compression
> 
> GeoPackage raster aim was initially for visualisation purposes, hence
> this default. The more analytic side was a later addition to the
> format, and actually an extension
> 
> Even
> 








  Roxo

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