[gdal-dev] Writing multi-bands vs multi-datasets

Thu Oct 14 12:03:49 PDT 2021

Even,

There are some issues with this way.

My draft Julia function looks like bellow  (tested with a MxNx7 array) but get this errors

julia> GMT.write_multiband(cube, "gd_cube.nc")
Warning 1: No 1D variable is indexed by dimension time
Warning 6: creation option '-co' is not formatted with the key=value format
Warning 6: creation option '-co' is not formatted with the key=value format
Warning 6: creation option '-co' is not formatted with the key=value format
ERROR 1: netcdf error #-45 : NetCDF: Not a valid data type or _FillValue type mismatch .
at (C:\programs\compa_libs\gdal_GIT\gdal\frmts\netcdf\netcdfdataset.cpp,netCDFDataset::CreateCopy,9012)

ERROR 1: netcdf error #-49 : NetCDF: Variable not found .
at (C:\programs\compa_libs\gdal_GIT\gdal\frmts\netcdf\netcdfdataset.cpp,NCDFPutAttr,10454)

Warning 1: No 1D variable is indexed by dimension time

And indeed the "time" variable shows up filled with 7 zeros when I open the nc file that is nevertheless created.
Also checked with getmetadataitem(ds, "NETCDF_DIM_time_VALUES")  that the "1,2,3,4,5,6,7" info was correctly set.

I's also strange the warnings about the "-co" options also because they were in fact taken into account. Omitting them creates a classic nc file.

function write_multiband(cube, fname::AbstractString, v=nothing; dim_name::String="time")
               nbands = size(cube,3)
               ds = gmt2gd(cube)
               Gdal.setmetadataitem(ds, "NETCDF_DIM_EXTRA", dim_name)
               Gdal.setmetadataitem(ds, "NETCDF_DIM_" * dim_name * "_DEF", "$(nbands),6")
               Gdal.setmetadataitem(ds, "NETCDF_DIM_" * dim_name * "_VALUES", "1,2,3,4,5,6,7")
               Gdal.setmetadataitem(ds, dim_name * "#axis", string(dim_name[1]))
               crs = Gdal.getproj(cube, wkt=true)
               (crs != "" ) && Gdal.setproj!(ds, crs)
               Gdal.unsafe_copy(ds, filename=fname, driver=getdriver("netCDF"), options=["-co", "FORMAT=NC4", "-co", "COMPRESS=DEFLATE", "-co", "ZLEVEL=4"])
end

From: Even Rouault <even.rouault at spatialys.com>
Sent: Sunday, October 10, 2021 10:48 PM
To: Joaquim Manuel Freire Luís <jluis at ualg.pt>; gdal-dev at lists.osgeo.org
Subject: Re: [gdal-dev] Writing multi-bands vs multi-datasets

Joaquim,

https://github.com/OSGeo/gdal/pull/4634 should hopefully help

Even
Le 10/10/2021 à 22:26, Joaquim Manuel Freire Luís a écrit :
Hi,

I have a Julia version of gdal_translate (that ends up calling GDALDatasetRasterIOEx) that works in saving a MxNxP array, but not the way I wanted.
It creates a multi-subdatasets file, whilst what I wished is to write a multi-band file.

For example, the file written with this Julia function looks like below

How can I write a multi-band instead of a multi-datasets?
I've been looking at the docs of GDALDatasetRasterIOEx but can't see any way of picking one or the other.

Joaquim

gdalinfo cube_rad.nc
Driver: netCDF/Network Common Data Format
Files: cube_rad.nc
Size is 512, 512
Metadata:
  NC_GLOBAL#Conventions=CF-1.5
  NC_GLOBAL#GDAL=GDAL 3.4.0dev, released 2021/99/99
  NC_GLOBAL#history=Sun Oct 10 13:01:06 2021: GDAL CreateCopy( cube_rad.nc, ... )
Subdatasets:
  SUBDATASET_1_NAME=NETCDF:"cube_rad.nc":Band1
  SUBDATASET_1_DESC=[1567x1519] Band1 (32-bit floating-point)
  SUBDATASET_2_NAME=NETCDF:"cube_rad.nc":Band2
  SUBDATASET_2_DESC=[1567x1519] Band2 (32-bit floating-point)
...

Saving the same data (or similar) from a Matlab code that I wrote long ago to stack grids, shows

gdalinfo evi_cube.nc
Driver: netCDF/Network Common Data Format
Files: evi_cube.nc
Size is 37, 59
Origin = (580140.000000000000000,4418550.000000000000000)
Pixel Size = (30.000000000000000,-30.000000000000000)
Metadata:
...
  latitude#actual_range={4416795,4418535}
  latitude#long_name=latitude
  latitude#units=degrees_north
  longitude#actual_range={580155,581235}
  longitude#long_name=longitude
  longitude#units=degrees_east
  NC_GLOBAL#Conventions=COARDS
  NC_GLOBAL#description=File written from Matlab
  NC_GLOBAL#node_offset=0
  NC_GLOBAL#Source_Software=Mirone
  NC_GLOBAL#title=Grid created by Mirone
  NETCDF_DIM_EXTRA={time}
  NETCDF_DIM_time_DEF={67,6}
  NETCDF_DIM_time_VALUES={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67}
  z#actual_range={-856.4703369140625,176.8457641601562}
  z#long_name=z
  z#units=unknown
  z#_FillValue=-nan(ind)
Corner Coordinates:
Upper Left  (  580140.000, 4418550.000)
Lower Left  (  580140.000, 4416780.000)
Upper Right (  581250.000, 4418550.000)
Lower Right (  581250.000, 4416780.000)
Center      (  580695.000, 4417665.000)
Band 1 Block=37x59 Type=Float32, ColorInterp=Undefined
  NoData Value=nan
  Unit Type: unknown
  Metadata:
    actual_range={-856.4703369140625,176.8457641601562}
    long_name=z
    NETCDF_DIM_time=1
    NETCDF_VARNAME=z
    units=unknown
    _FillValue=-nan(ind)
Band 2 Block=37x59 Type=Float32, ColorInterp=Undefined
  NoData Value=nan
  Unit Type: unknown
  Metadata:
    actual_range={-856.4703369140625,176.8457641601562}
    long_name=z
    NETCDF_DIM_time=2
    NETCDF_VARNAME=z
    units=unknown
    _FillValue=-nan(ind)
...

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