rasterize into NetCDF file gives cryptic error if NCDataset is not loaded

[felixcremer]

When I am trying to rasterize into a netcdf file I get the following error and this is not really clear why this is not working. For a .tif file I get a better error message and also for loading a NetCDF.
The same happens for Zarr files.

using Rasters
julia> pointvec = [
           (-20.0, 30.0),
           (-20.0, 10.0),
           (0.0, 10.0),
           (0.0, 30.0),
           (-20.0, 30.0),
       ]
julia> rasterize(count, pointvec, filename="/tmp/rasterizetest.nc", size=10)
ERROR: ArgumentError: `sourceconstructor` is not defined for Rasters.NCDsource
Stacktrace:
  [1] sourceconstructor(s::Type{Rasters.NCDsource})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/sources/sources.jl:77
  [2] sourceconstructor(source::Rasters.NCDsource)
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/sources/sources.jl:76
  [3] write(filename::String, source::Rasters.NCDsource, A::Raster{…}; append::Bool, force::Bool, kw::@Kwargs{…})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/sources/commondatamodel.jl:475
  [4] write(::Function, ::String, ::Vararg{…}; kw::@Kwargs{…})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/write.jl:207
  [5] write(::Function, ::Function, ::Vararg{…}; kw::@Kwargs{…})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/write.jl:207
  [6] create(filename::String, source::Rasters.NCDsource, ::Type{…}, dims::Tuple{…}; name::Symbol, missingval::Int64, fill::Int64, metadata::Metadata{…}, chunks::Rasters.NoKW, scale::Rasters.NoKW, offset::Rasters.NoKW, dropband::Bool, lazy::Bool, verbose::Bool, force::Bool, coerce::Rasters.NoKW, f::Rasters.var"#625#626"{…}, kw::@Kwargs{})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/create.jl:301
  [7] create(filename::String, T::Type{…}, dims::Tuple{…}; lazy::Bool, parent::Rasters.NoKW, suffix::String, source::Rasters.NCDsource, missingval::Int64, kw::@Kwargs{…})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/create.jl:182
  [8] create(::Function, ::String, ::Vararg{Any}; kw::@Kwargs{fill::Int64, name::Symbol, missingval::Int64, metadata::Metadata{Nothing, Dict{Any, Any}}, suffix::String})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/create.jl:129
  [9] #alloc_rasterize#623
    @ ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:490 [inlined]
 [10] alloc_rasterize
    @ ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:480 [inlined]
 [11] create_rasterize_dest
    @ ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:474 [inlined]
 [12] create_rasterize_dest(f::Function, r::Rasters.RasterCreator{DataType, Tuple{X{Sampled{…}}, Y{Sampled{…}}}, Metadata{Nothing, Dict{Any, Any}}, Int64, Rasters.NoKW, Rasters.NoKW})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:455
 [13] rasterize(data::Vector{…}; to::Nothing, fill::Function, threaded::Bool, geometrycolumn::Nothing, kw::@Kwargs{…})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:443
 [14] rasterize
    @ ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:439 [inlined]
 [15] #rasterize#614
    @ ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:430 [inlined]
 [16] top-level scope
    @ REPL[19]:1
Some type information was truncated. Use `show(err)` to see complete types.

This is the error for a .tif file. There it is clear what I did wrong.

julia> rasterize(count, pointvec, filename="/tmp/rasterizetest.tif", size=10)
ERROR: Missing package extension for Rasters.GDALsource(). Run `using ArchGDAL` before using `write` for this file extension.
Stacktrace:
  [1] error(s::String)
    @ Base ./error.jl:44
  [2] write(filename::String, source::Rasters.GDALsource, A::Raster{…}; kw::@Kwargs{…})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/write.jl:75
  [3] write(::Function, ::String, ::Vararg{…}; kw::@Kwargs{…})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/write.jl:207
  [4] write(::Function, ::Function, ::Vararg{…}; kw::@Kwargs{…})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/write.jl:207
  [5] create(filename::String, source::Rasters.GDALsource, ::Type{…}, dims::Tuple{…}; name::Symbol, missingval::Int64, fill::Int64, metadata::Metadata{…}, chunks::Rasters.NoKW, scale::Rasters.NoKW, offset::Rasters.NoKW, dropband::Bool, lazy::Bool, verbose::Bool, force::Bool, coerce::Rasters.NoKW, f::Rasters.var"#625#626"{…}, kw::@Kwargs{})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/create.jl:301
  [6] create(filename::String, T::Type{…}, dims::Tuple{…}; lazy::Bool, parent::Rasters.NoKW, suffix::String, source::Rasters.GDALsource, missingval::Int64, kw::@Kwargs{…})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/create.jl:182
  [7] create(::Function, ::String, ::Vararg{Any}; kw::@Kwargs{fill::Int64, name::Symbol, missingval::Int64, metadata::Metadata{Nothing, Dict{Any, Any}}, suffix::String})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/create.jl:129
  [8] #alloc_rasterize#623
    @ ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:490 [inlined]
  [9] alloc_rasterize
    @ ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:480 [inlined]
 [10] create_rasterize_dest
    @ ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:474 [inlined]
 [11] create_rasterize_dest(f::Function, r::Rasters.RasterCreator{DataType, Tuple{X{Sampled{…}}, Y{Sampled{…}}}, Metadata{Nothing, Dict{Any, Any}}, Int64, Rasters.NoKW, Rasters.NoKW})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:455
 [12] rasterize(data::Vector{…}; to::Nothing, fill::Function, threaded::Bool, geometrycolumn::Nothing, kw::@Kwargs{…})
    @ Rasters ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:443
 [13] rasterize
    @ ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:439 [inlined]
 [14] #rasterize#614
    @ ~/.julia/packages/Rasters/G6rYV/src/methods/rasterize.jl:430 [inlined]
 [15] top-level scope
    @ REPL[17]:1
Some type information was truncated. Use `show(err)` to see complete types.

[tiemvanderdeure]

Both of those should call BackendException.

[asinghvi17]

ERROR: Missing package extension for Rasters.GDALsource(). Run using ArchGDAL before using write for this file extension.

could be

ERROR: `ArchGDAL` is required to use this functionality but is not loaded.  
Run `using ArchGDAL` before using `write` for this file extension.

which seems better from a user perspective because it tells them what's actually wrong.

[tiemvanderdeure]

Isn't that very similar to what a BackendException would throw?

I think using the more generic error BackendException is a bit more practical - e.g. in this case the user never calls write, so it could be confusing to refer to that function specifically

[asinghvi17]

Sure, but from a new user perspective, what's a backend and what's an extension? I just want to load my data :D

Maybe BackendException could have an extra message, and the base message could be:

ERROR: `ArchGDAL` is required to use this functionality but is not loaded.  
Run `using ArchGDAL` to enable this functionality.

with an extra message field that can add context

[tiemvanderdeure]

I guess the error message was written before we added a bunch of extensions for other things and never changes.

The word "backends" doesn't make a whole lot of sense when trying to resample or calculate cellarea, but I mean it does the job

julia> cellarea(Spherical(), ras)
ERROR: Rasters.jl requires backends to be loaded manually.  Run `import Proj` to fix this error.
Stacktrace: