Add prototype for GMTgrid -> Raster conversion

examples/gmt/raster_convert.jl

@@ -0,0 +1,51 @@
+using GMT, Rasters
+import GeoFormatTypes as GFT
+
+function trunc_string_at_null(s::String)
+    isempty(s) && return s
+    idx = findfirst(isequal('\0'), s)
+    isnothing(idx) && return s
+    return s[1:idx-1]
+end
+
+function _get_crs(G::GMT.GMTgrid)
+    epsg = G.epsg
+    epsg ≤ 0 || return GFT.EPSG(epsg)
+    wkt = trunc_string_at_null(G.wkt)
+    isempty(wkt) || return GFT.WellKnownText(GFT.CRS(), wkt)
+    proj4 = trunc_string_at_null(G.proj4)
+    isempty(proj4) || return GFT.ProjString(proj4)
+    if G.geog == -1 || G.geog == 1 # yes, is geographic coords
+        GFT.EPSG(4326) # default to WGS84
+    elseif G.geog == 0 # unknown, not geographic coords
+        GFT.EPSG(0) # default to UTM
+    end
+end
+
+function _get_metadata(G::GMT.GMTgrid)
+
+end
+
+function Base.convert(::Type{Raster}, G::GMT.GMTgrid{T, N}) where {T, N}
+    crs = _get_crs(G)
+    metadata = _get_metadata(G)
+    missingval = G.nodata
+    sampling = nothing # get this from G.registration
+    xs = Rasters.X(G.x)
+    ys = Rasters.Y(G.y)
+    if N == 3
+        # do something with vs
+    end
+    zs = G.z # reorder!
+
+    dims = (xs, ys)
+    if N == 3
+        dims = (xs, ys, vs)
+    end
+
+    return Raster(
+        zs; 
+        dims, crs, metadata, missingval,
+    )
+end
+