computes km grid to gpx

kmgrid2.lua

-- kmgrid

local push = table.insert

-- délka rovnoběžky
function latLen(lat)
    local d = 40074
    return d * math.cos(math.rad(lat))
end

-- jedna horizontalni linka bodu
function horizontal(out, amount, lat, lon)
    local horiKmLen = 360/latLen(lat)

    for y=-amount,amount do
        push(out, lat ..','.. (lon + (y*horiKmLen)) )
        print(' <wpt lat="'..lat..'" lon="'..(lon + (y*horiKmLen))..'"/>')
    end

    return out
end


local coords = {}
local vertKmLen = 360/latLen(0)
local amount = 5

lat=0
lon=0
print('<gpx version="1.1" creator="kmgrid">')
for i=-amount,amount do
    horizontal(coords, amount, lat + (i*vertKmLen), lon)
end
print('</gpx>')