Switch from missing to nothing

This is for two reasons:

1. The nodata value isn't meant to be used as a "sentinel value" in the raster output. If ArchGDAL wants to provide a convenience function for returning `Array{Union{T, Missing}}`, the treatment of missing data should be based on the appropriate use of `getmaskband()` (https://trac.osgeo.org/gdal/wiki/rfc15_nodatabitmask for details).

2. Even if ArchGDAL does provide a convenience function for returning `Array{Union{T, Missing}}`, the proper place for using `missing` values is in the array being constructed, and not the value being returned from `getnodatavalue(band)`.

src/raster/rasterband.jl

@@ -176,15 +176,15 @@ end
 
 Fetch the no data value for this band.
 
-If there is no out of data value, `missing` will be returned instead. The no
+If there is no out of data value, `nothing` will be returned instead. The no
 data value for a band is generally a special marker value used to mark pixels
 that are not valid data. Such pixels should generally not be displayed, nor
 contribute to analysis operations.
 
 ### Returns
-the nodata value for this band or `missing`.
+the nodata value for this band or `nothing`.
 """
-function getnodatavalue(band::AbstractRasterBand)::Union{Float64,Missing}
+function getnodatavalue(band::AbstractRasterBand)::Union{Float64,Nothing}
     # ### Parameters
     # * `pbSuccess`   pointer to a boolean to use to indicate if a value is
     #     actually associated with this layer. May be `NULL` (default).
@@ -193,7 +193,7 @@ function getnodatavalue(band::AbstractRasterBand)::Union{Float64,Missing}
     return if Bool(hasnodatavalue[])
         nodatavalue
     else
-        missing
+        nothing
     end
 end
 

test/test_display.jl

@@ -68,7 +68,7 @@ const AG = ArchGDAL;
 
             @test sprint(print, AG.getband(dataset, 1)) == """
             [GA_ReadOnly] Band 1 (Red): 2048 x 1024 (UInt8)
-                blocksize: 256×256, nodata: missing, units: 1.0px + 0.0
+                blocksize: 256×256, nodata: nothing, units: 1.0px + 0.0
                 overviews: (0) 1024x512 (1) 512x256 (2) 256x128 
                            (3) 128x64 (4) 64x32 (5) 32x16 
                            (6) 16x8 """

test/test_ospy_examples.jl

@@ -385,7 +385,7 @@ const AG = ArchGDAL;
                     outband = AG.getband(outDS, 1)
                     @test sprint(print, outband) == """
                     [GA_Update] Band 1 (Undefined): 5665 x 5033 (Float32)
-                        blocksize: 5665×1, nodata: missing, units: 1.0px + 0.0
+                        blocksize: 5665×1, nodata: nothing, units: 1.0px + 0.0
                         overviews: """
                     AG.setnodatavalue!(outband, -99)
                     # georeference the image and set the projection
@@ -484,7 +484,7 @@ const AG = ArchGDAL;
                     bandout = AG.getband(dsout, 1)
                     @test sprint(print, bandout) == """
                     [GA_Update] Band 1 (Undefined): 4500 x 3000 (UInt8)
-                        blocksize: 4500×1, nodata: missing, units: 1.0px + 0.0
+                        blocksize: 4500×1, nodata: nothing, units: 1.0px + 0.0
                         overviews: """
 
                     # set the geotransform and projection on the output

test/test_rasterband.jl

@@ -43,25 +43,25 @@ const AG = ArchGDAL;
             AG.setscale!(rb, 1)
             @test AG.getscale(rb) ≈ 1
 
-            @test ismissing(AG.getnodatavalue(rb))
+            @test isnothing(AG.getnodatavalue(rb))
             AG.setnodatavalue!(rb, -100)
             @test AG.getnodatavalue(rb) ≈ -100
             AG.deletenodatavalue!(rb)
-            @test ismissing(AG.getnodatavalue(rb))
+            @test isnothing(AG.getnodatavalue(rb))
 
             AG.copy(dataset) do dest
                 destband = AG.getband(dest, 1)
                 AG.copywholeraster!(rb, destband)
                 @test sprint(print, destband) == """
                 [GA_Update] Band 1 (Gray): 100 x 100 (UInt8)
-                    blocksize: 100×81, nodata: missing, units: 1.0px + 0.0
+                    blocksize: 100×81, nodata: nothing, units: 1.0px + 0.0
                     overviews: """
                 @test AG.noverview(destband) == 0
                 AG.buildoverviews!(dest, Cint[2, 4, 8])
                 @test AG.noverview(destband) == 3
                 @test sprint(print, destband) == """
                 [GA_Update] Band 1 (Gray): 100 x 100 (UInt8)
-                    blocksize: 100×81, nodata: missing, units: 1.0px + 0.0
+                    blocksize: 100×81, nodata: nothing, units: 1.0px + 0.0
                     overviews: (0) 50x50 (1) 25x25 (2) 13x13 
                                """
                 @test AG.getcolorinterp(destband) == AG.GCI_GrayIndex
@@ -70,25 +70,25 @@ const AG = ArchGDAL;
 
                 @test sprint(print, AG.sampleoverview(destband, 100)) == """
                 [GA_Update] Band 1 (Gray): 13 x 13 (UInt8)
-                    blocksize: 128×128, nodata: missing, units: 1.0px + 0.0
+                    blocksize: 128×128, nodata: nothing, units: 1.0px + 0.0
                     overviews: """
                 @test sprint(print, AG.sampleoverview(destband, 200)) == """
                 [GA_Update] Band 1 (Gray): 25 x 25 (UInt8)
-                    blocksize: 128×128, nodata: missing, units: 1.0px + 0.0
+                    blocksize: 128×128, nodata: nothing, units: 1.0px + 0.0
                     overviews: """
                 @test sprint(print, AG.sampleoverview(destband, 500)) == """
                 [GA_Update] Band 1 (Gray): 25 x 25 (UInt8)
-                    blocksize: 128×128, nodata: missing, units: 1.0px + 0.0
+                    blocksize: 128×128, nodata: nothing, units: 1.0px + 0.0
                     overviews: """
                 AG.sampleoverview(destband, 1000) do result
                     @test sprint(print, result) == """
                     [GA_Update] Band 1 (Gray): 50 x 50 (UInt8)
-                        blocksize: 128×128, nodata: missing, units: 1.0px + 0.0
+                        blocksize: 128×128, nodata: nothing, units: 1.0px + 0.0
                         overviews: """
                 end
                 @test sprint(print, AG.getmaskband(destband)) == """
                 [GA_ReadOnly] Band 0 (Undefined): 100 x 100 (UInt8)
-                    blocksize: 100×81, nodata: missing, units: 1.0px + 0.0
+                    blocksize: 100×81, nodata: nothing, units: 1.0px + 0.0
                     overviews: """
                 @test AG.maskflags(destband) == 1
                 @test AG.maskflaginfo(rb) == (
@@ -101,7 +101,7 @@ const AG = ArchGDAL;
                 AG.getmaskband(destband) do maskband
                     @test sprint(print, maskband) == """
                     [GA_Update] Band 1 (Gray): 100 x 100 (UInt8)
-                        blocksize: 100×81, nodata: missing, units: 1.0px + 0.0
+                        blocksize: 100×81, nodata: nothing, units: 1.0px + 0.0
                         overviews: """
                 end
                 @test AG.maskflags(destband) == 3