Getting metadata on single band geotiff?

[rafaqz]

Trying to get the band of single band datasets with ArchGDAL.getband(dataset, 1) is giving me a ReadOnlyMemoryError()` (is that expected?)

Without the band object there are no methods like getnodatavalue, how else can I get that information? (as separate values, not gdalinfo text)

[yeesian]

That's strange, since the REPL display is based on calling it with ArchGDAL.getband(dataset, i). Do you have an example to produce the ReadOnlyMemoryError()?

[rafaqz]

Oops I was passing the band outside of the closure.

[AmebaBrain]

Same error for me. Sometimes I get ReadOnlyMemoryError(). In other case it is Segmentation fault

$ julia
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.1.0 (2019-01-21)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> import GDAL

julia> import ArchGDAL; const AG = ArchGDAL
ArchGDAL

julia> filepath = "../data/geo/world.tif"
"../data/geo/world.tif"

julia> AG.registerdrivers() do
           AG.read(filepath) do dataset
               println(dataset)
               #println(typeof(dataset))
               #println(AG.filelist(dataset))
               #println(AG.nraster(dataset))
               #println(AG.width(dataset))
               #println(AG.height(dataset))
       
               ds = AG.getband(dataset, 1)
           end
       end
GDAL Dataset (Driver: GTiff/GeoTIFF)
File(s): 
  ../data/geo/world.tif

Dataset (width x height): 2048 x 1024 (pixels)
Number of raster bands: 3
  [GA_ReadOnly] Band 1 (Red): 2048 x 1024 (UInt8)
  [GA_ReadOnly] Band 2 (Green): 2048 x 1024 (UInt8)
  [GA_ReadOnly] Band 3 (Blue): 2048 x 1024 (UInt8)


signal (11): Segmentation fault
in expression starting at no file:0
unknown function (ip: 0xfffffffffffffff7)
show at /home/toleg/.julia/packages/ArchGDAL/RCmkd/src/base/display.jl:62
show at ./sysimg.jl:194
jl_fptr_trampoline at /buildworker/worker/package_linux64/build/src/gf.c:1864
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
display at /home/toleg/.julia/packages/OhMyREPL/GFHgr/src/output_prompt_overwrite.jl:6
jl_fptr_trampoline at /buildworker/worker/package_linux64/build/src/gf.c:1864
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
display at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/REPL/src/REPL.jl:135
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
display at ./multimedia.jl:287
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1571 [inlined]
jl_f__apply at /buildworker/worker/package_linux64/build/src/builtins.c:556
jl_f__apply_latest at /buildworker/worker/package_linux64/build/src/builtins.c:594
#invokelatest#1 at ./essentials.jl:742 [inlined]
invokelatest at ./essentials.jl:741 [inlined]
print_response at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/REPL/src/REPL.jl:155
print_response at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/REPL/src/REPL.jl:140
jfptr_print_response_13372.clone_1 at /home/toleg/Install/julia-1.1.0/lib/julia/sys.so (unknown line)
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
do_respond at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/REPL/src/REPL.jl:714
unknown function (ip: 0x7fe9fa3a2ea4)
jl_fptr_trampoline at /buildworker/worker/package_linux64/build/src/gf.c:1864
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1571 [inlined]
jl_f__apply at /buildworker/worker/package_linux64/build/src/builtins.c:556
jl_f__apply_latest at /buildworker/worker/package_linux64/build/src/builtins.c:594
#invokelatest#1 at ./essentials.jl:742 [inlined]
invokelatest at ./essentials.jl:741 [inlined]
run_interface at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/REPL/src/LineEdit.jl:2273
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
run_frontend at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/REPL/src/REPL.jl:1035
run_repl at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/REPL/src/REPL.jl:192
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
#734 at ./client.jl:362
jfptr_#734_6031.clone_1 at /home/toleg/Install/julia-1.1.0/lib/julia/sys.so (unknown line)
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1571 [inlined]
jl_f__apply at /buildworker/worker/package_linux64/build/src/builtins.c:556
jl_f__apply_latest at /buildworker/worker/package_linux64/build/src/builtins.c:594
#invokelatest#1 at ./essentials.jl:742 [inlined]
invokelatest at ./essentials.jl:741 [inlined]
run_main_repl at ./client.jl:346
exec_options at ./client.jl:284
_start at ./client.jl:436
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
unknown function (ip: 0x40191d)
unknown function (ip: 0x401523)
__libc_start_main at /lib64/libc.so.6 (unknown line)
unknown function (ip: 0x4015c4)
Allocations: 15081790 (Pool: 15078623; Big: 3167); GC: 33
Segmentation fault (Speicherabzug geschrieben)

[visr]

@AmebaBrain this happens because the band ds that you take out of the do block relies on the parent dataset existing. As soon as the AG.read(filepath) do dataset block finishes, it is cleaned up, making the band unusable. So you have to basically do what you want inside the do block. Of course if you load the band into a julia array that does not rely on a GDAL object existing you can use that afterward.

Note that in #76 interactive datasets are added that make it easier to do this in the repl without having to worry about issues like this.

[AmebaBrain]

@visr
Got it, thanks. Did as you suggested

AG.registerdrivers() do
    AG.read(filepath) do dataset
        # raster band is linked to dataset. we have to read raster data into array
        global data = AG.read(dataset, 1)
    end
end