Minetest OS Mapgen

init.lua

-- OS MAP READER
--    by rubenwardy
-- incomplete
-- CC BY SA
-- =================

osmapgen = {
	_api = "http://maps.googleapis.com/maps/api/elevation/json?",
	url = {},
	data = {}
}

function osmapgen.get_height(x,z)
	-- Check to see if it has been requested before
	for i=1, #osmapgen.data do
		local val = osmapgen.data[i]
		if (val.x == x and val.z == z) then
			return val.h
		end
	end
	
	-- Request it
	osmapgen.url.request({
		sensor=false,
		locations=x..","..z
	})
	
	if not osmapgen.result then
		return 0
	else
		local id = string.match(osmapgen.result.result, '"elevation" : ([-0123456789]+)')
		print (id)
	end
end

function osmapgen.url.request(params)
	local res = ""
	
	for key,val in pairs(params) do
		if (res~="") then
			res = res.."&"
		end
		if val then
			res = res.. key .. "=" .. val
		else
			print("Value is empty!")
		end
	end
	print (osmapgen._api..res)
	
	if minetest.download_http then
		osmapgen.result = nil
		minetest.download_http(osmapgen._api..res, 10, osmapgen.url._result)

		local start = os.clock()
		while (not osmapgen.result) do
			if (os.clock()>start+10) then
				print("DOWNLOAD TIMEOUT")
				return
			end
		end
	elseif io.popen then
		local dl,err = io.popen("curl --url "..osmapgen._api..res, "r")
		
		if not dl the
			--throw("OSMAPGEN: There is no way to download data."..err)
			osmapgen.result = {result='"elevation" : 10'}
			return
		end

		osmapgen.result = {dl=dl}
	end
end

function osmapgen.url._result(result,code)
	osmapgen.result = {result = result, code = code}
end

-- Initialise
function osmapgen.init()
	if (not minetest.download_http) then
		if (not io.popen) then
			throw("OSMAPGEN: There is no way to download data.")
		else
			print("")
			print("[WARNING!] You do not have a lua curl build.")
			print("Delays will occur as the data is being downloaded.")
			print("")
		end
	end
end

-- Set up mapgeneration call back
minetest.register_on_mapgen_init(function(mgparams)
	minetest.set_mapgen_params({mgname="singlenode", flags="nolight", flagmask="nolight"})
end)

minetest.register_on_generated(function(minp, maxp, seed)
	-- Start timer
	local t1 = os.clock()
	
	-- Get voxel manipulator
	local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
	local a = VoxelArea:new{
	MinEdge={x=emin.x, y=emin.y, z=emin.z},
		MaxEdge={x=emax.x, y=emax.y, z=emax.z},
	}
	local data = vm:get_data()
	
	-- Content Id
	local c_dirt  = minetest.get_content_id("default:dirt")
	local c_grass = minetest.get_content_id("default:dirt_with_grass")
	local c_water = minetest.get_content_id("default:water_source")

	local sidelen = maxp.x - minp.x + 1

	for z = minp.z, maxp.z do
		for x = minp.x, maxp.x do
			local h = 0 --osmapgen.get_height(x,z)
			for y = minp.y, maxp.y do
				-- Do mapgeneration
				if y<h-5 then
					local vi = a:index(x, y, z)
                        		data[vi] = c_stone
                        	elseif y<h then
                        		local vi = a:index(x, y, z)
                        		data[vi] = c_dirt
                        	elseif y=h then
                        		local vi = a:index(x, y, z)
                        		data[vi] = c_grass
				end
			end
		end
	end

	vm:set_data(data)
	vm:calc_lighting(
		{x=minp.x-16, y=minp.y, z=minp.z-16},
		{x=maxp.x+16, y=maxp.y, z=maxp.z+16}
	)

	vm:write_to_map(data)

	print(string.format("elapsed time: %.2fms", (os.clock() - t1) * 1000))
end)

-- Init
osmapgen.init()

You are missing this code:

local c_stone = minetest.get_content_id("default:stone")