many worldgen mods and gonna try technic now

mods/dfcaverns/mapgen_helper/voxeldata.lua

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+-- similar to iter_xyz, but iterates first along the y axis. Useful in mapgens that want to detect a vertical transition (eg, finding ground level)
+function VoxelArea:iter_yxz(minx, miny, minz, maxx, maxy, maxz)
+	local i = self:index(minx, miny, minz) - self.ystride
+	
+	local x = minx
+	local y = miny - 1
+	local z = minz
+
+	return function()
+		y = y + 1
+
+		if y <= maxy then
+			i = i + self.ystride
+			return i, x, y, z
+		end
+		
+		y = miny
+		x = x + 1
+		
+		if x <= maxx then
+			i = self:index(x, y, z)
+			return i, x, y, z
+		end
+		
+		x = minx
+		z = z + 1
+		
+		if z <= maxz then
+			i = self:index(x, y, z)
+			return i, x, y, z
+		end
+	end
+end
+
+function VoxelArea:iterp_yxz(minp, maxp)
+	return self:iter_yxz(minp.x, minp.y, minp.z, maxp.x, maxp.y, maxp.z)
+end
+
+function VoxelArea:get_y(i)
+	return math.floor(((i - 1) % self.zstride) / self.ystride) + self.MinEdge.y
+end
+
+-- Used to make transform more efficient by skipping a table creation
+function VoxelArea:position_xyz(vi)
+	local MinEdge = self.MinEdge
+	local Zstride = self.zstride
+	local Ystride = self.ystride
+	vi = vi - 1
+	local z = math.floor(vi / Zstride) + MinEdge.z
+	vi = vi % Zstride
+	local y = math.floor(vi / Ystride) + MinEdge.y
+	vi = vi % Ystride
+	local x = vi + MinEdge.x
+	return x, y, z
+end
+
+-- Takes another voxelarea and an index in it and transforms it into an index into its own
+-- voxelarea, or nil if it's not in the voxelarea. This is useful when you've got, for example,
+-- a mapgen's voxelmanipulator and a perlin noise array covering the map block but not the entire
+-- emerged volume.
+function VoxelArea:transform(area, vi)
+	local x,y,z = area:position_xyz(vi)
+	if self:contains(x,y,z) then
+		return self:index(x,y,z)
+	end
+	return nil
+end