writeRaster does not preserve names when writing to NetCDF

Hi,

I don't think that NetCDF has the capacity to store these names in a
natural way. Internally your brick is stored as a NetCDF variable, in
this case a 3d array. To do this it would need to define a 'dimension"
and include a lookup map to the names. A NetCDF dimension variable
must be populated with numbers I believe, so you would need another
variable to store those and then add in features to raster to use
them.

There's at least two blockers here:
- the NetCDF model is not designed for storing tabular data (a RGB
image is a table of records in one sense, not a 3d array of integers)
- gridded data storage usually conflates "dimension" with
"attributes", which is unfortunate.

On Tue, Aug 12, 2014 at 12:26 AM, Mark Payne <markpayneatwork at gmail.com> wrote:

Hi,

I have a problem with writeRaster when writing a brick to NetCDF - the
names of the layers are not preserved. Here is a minimum example to
demonstrate the point:

#Create an arbitrary brick and write it out
b <- brick(system.file("external/rlogo.grd", package="raster"))
fname <- file.path( tempdir(),"test.nc")
dmp <- writeRaster(b,file=fname)

#Now read it back in
a <- brick(fname)

#However, names are not preserved

names(b)

[1] "red"   "green" "blue"

names(a)

[1] "X1" "X2" "X3"

I realise this is a touch tricky, as NetCDF isn't exactly made for storing
character strings, which is how raster stores the layer names. However,
there are many cases where the string is just a representation of a number
anyway.... e.g. when working with time or depth levels as the layers in the
brick. One solution could therefore be to allow the writeRaster function to
take an argument "zvals", in the same way that it takes "zname" and "zunit"
when working with netcdf files - this argument would let you specify the
numeric values of the z-axis. Everything else would then work ok I think,
as brick() picks up the values of the z-axis, converts them to strings and
assigns them to layer names.

Cheers,

Mark

raster version: 2.2-31
R version 3.0.3
ncdf4 version: 1.10
Platform: Linux Mint 16, 64 bit

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--
Michael Sumner
Software and Database Engineer
Australian Antarctic Division
Hobart, Australia
e-mail: mdsumner at gmail.com