ground_obj.lua

--[[
Call this file with the height input file and the desired output file as arguments.
example: lua ground_obj.lua hieght.txt ground.obj
]]--

-- Read the input height values.
input = io.open(arg[1], "r")
heights = {}
for line in input:lines() do
    table.insert(heights, tonumber(line))
end
io.close(input)

-- Write the output obj file.
output = io.open(arg[2], "w")
for x = 0, 256, 1 do
    for y = 0, 256, 1 do
        output:write("v ", x, " ", y, " ", heights[x*256+y+1], "\n")
    end
end
for i = 0, 256, 1 do
    for j = 1, 256, 1 do
        output:write("f ", (i*257)+j, " ", (i*257)+j+1, " ", (257*(i+1))+j+1, " ", (257*(i+1))+j, "\n")
    end
end
io.close(output)

random_height.lua

-- This generates a file full of random height values that can be used to test the above script.
output = io.open("height.txt", "w")
for i = 1, 66049, 1 do
    output:write(math.random(3), "\n")
end
io.close(output)