Add metadata function (#2)

* Add 'metadata' function

* Add missing parameters

* Update comments

* Update kwargs

* Update code order

* Rename arguments

* Fix code

src/GeoTIFF.jl

@@ -11,6 +11,7 @@ using FixedPointNumbers: Fixed, Normed
 
 import TiffImages
 
+include("geokeys.jl")
 include("metadata.jl")
 include("image.jl")
 include("load.jl")

src/geokeys.jl

@@ -0,0 +1,76 @@
+# -----------------------------------------------------------------
+# Licensed under the MIT License. See LICENSE in the project root.
+# -----------------------------------------------------------------
+
+@enum GeoKeyID::UInt16 begin
+  GTRasterTypeGeoKey = 1025
+  GTModelTypeGeoKey = 1024
+  ProjectedCRSGeoKey = 3072
+  GeodeticCRSGeoKey = 2048
+  VerticalGeoKey = 4096
+  GTCitationGeoKey = 1026
+  GeodeticCitationGeoKey = 2049
+  ProjectedCitationGeoKey = 3073
+  VerticalCitationGeoKey = 4097
+  GeogAngularUnitsGeoKey = 2054
+  GeogAzimuthUnitsGeoKey = 2060
+  GeogLinearUnitsGeoKey = 2052
+  ProjLinearUnitsGeoKey = 3076
+  VerticalUnitsGeoKey = 4099
+  GeogAngularUnitSizeGeoKey = 2055
+  GeogLinearUnitSizeGeoKey = 2053
+  ProjLinearUnitSizeGeoKey = 3077
+  GeodeticDatumGeoKey = 2050
+  PrimeMeridianGeoKey = 2051
+  PrimeMeridianLongitudeGeoKey = 2061
+  EllipsoidGeoKey = 2056
+  EllipsoidSemiMajorAxisGeoKey = 2057
+  EllipsoidSemiMinorAxisGeoKey = 2058
+  EllipsoidInvFlatteningGeoKey = 2059
+  VerticalDatumGeoKey = 4098
+  ProjectionGeoKey = 3074
+  ProjMethodGeoKey = 3075
+  ProjStdParallel1GeoKey = 3078
+  ProjStdParallel2GeoKey = 3079
+  ProjNatOriginLongGeoKey = 3080
+  ProjNatOriginLatGeoKey = 3081
+  ProjFalseOriginLongGeoKey = 3084
+  ProjFalseOriginLatGeoKey = 3085
+  ProjCenterLongGeoKey = 3088
+  ProjCenterLatGeoKey = 3089
+  ProjStraightVertPoleLongGeoKey = 3095
+  ProjAzimuthAngleGeoKey = 3094
+  ProjFalseEastingGeoKey = 3082
+  ProjFalseNorthingGeoKey = 3083
+  ProjFalseOriginEastingGeoKey = 3086
+  ProjFalseOriginNorthingGeoKey = 3087
+  ProjCenterEastingGeoKey = 3090
+  ProjCenterNorthingGeoKey = 3091
+  ProjScaleAtNatOriginGeoKey = 3092
+  ProjScaleAtCenterGeoKey = 3093
+end
+
+# Corresponding names in the GeoTIFF specification:
+# id - KeyID
+# tag - TIFFTagLocation
+# count - Count
+# value - ValueOffset
+struct GeoKey
+  id::GeoKeyID
+  tag::UInt16
+  count::UInt16
+  value::UInt16
+end
+
+# generic values
+const Undefined = UInt16(0)
+const UserDefined = UInt16(32767)
+
+# GTRasterTypeGeoKey values
+const PixelIsArea = UInt16(1)
+const PixelIsPoint = UInt16(2)
+
+# GTModelTypeGeoKey values
+const Projected2D = UInt16(1)
+const Geographic2D = UInt16(2)
+const Geocentric3D = UInt16(3)