# Module:Infobox dim

require('strict')
local getArgs = require('Module:Arguments').getArgs
local p = {}  
local log2 = 0.693147181
local ppm = 1000/0.3 -- pixels per meter, from 0.3 mm / pixel from https://wiki.openstreetmap.org/wiki/Zoom_levels  
-- To convert to OSM zoom level, we need to know meters per pixel at zoom level 9
-- On the equator, it's 305.748 meters/pixel according to https://wiki.openstreetmap.org/wiki/Zoom_levels
-- This quantity depends on the latitude (which we don't have easy access to)
-- Instead, we'll be correct at 38 degrees N, given en-WP bias towards NA and Europe
-- 38N was chosen because:
-- * It's the furthest north where scale=100000 maps to zoom=12
-- * One hemisphere (20000km) maps to zoom=1
local metersPerPixelLevel9 = 305.748*math.cos(math.rad(38))  
-- Convert from Geohack's scale to OSM style zoom levels as used by <maplink>
local function geohackScaleToMapZoom(scale)
scale = tonumber(scale)
if not scale or scale <= 0 then return end
return math.log(metersPerPixelLevel9*ppm/scale)/log2 + 9
end  
-- compute the viewport size (on screen) in meters, assuming ppm pixels per meter on screen
local function computeViewport(args)
local viewport_cm = tonumber(args.viewport_cm)
local viewport_px = tonumber(args.viewport_px)
return viewport_cm and viewport_cm / 100 or viewport_px and viewport_px / ppm
or tonumber(args.default_viewport) or 0.1
end  
-- convert from geohack dim (knowing the viewpoint size on screen) to geohack scale
local function geohackDimToScale(dim, args)
dim = tonumber(dim)
args = args or {}
if not dim or dim <= 0 then return end
local units = args.units
if units and string.lower(units) == 'km' then
dim = dim*1000
end
return dim / computeViewport(args)
end  
-- inverse of above function, returning dim in km
local function geohackScaleToDim(scale, args)
scale = tonumber(scale)
args = args or {}
if not scale or scale <= 0 then return end
return scale * computeViewport(args) * 1e-3
end  
local oddShape = 2.09 --- length/sqrt(area) of Boston (to choose an example)  
-- Convert from Geohack's types to Geohack dim
local function geohackTypeToDim(args)
local t = args.type
if not t then return end
local typeDim = mw.loadData('Module:Infobox_dim/data')
local dim = typeDim[t]
local population = tonumber(args.population)
if t == 'city' and population and population > 0 then
-- assume city is a circle with density of 1000/square kilometer
-- compute diameter, in meters. Then multiply by oddShape to account for weird shapes
dim = 35.68e-3*math.sqrt(population)*oddShape
-- don't zoom in too far
if dim < 5 then
dim = 5
end
end
return dim
end  
-- Convert from dimension of object to Geohack dim
local function computeDim(length,width,area)
if length and width then
return math.max(length,width)
end
if length then return length end
if width then return width end
if area then return oddShape*math.sqrt(area) end
end  
-- compute geohack dim from unit arguments (e.g., length_mi)
local function convertDim(args)
local length = args.length_mi and 1.60934*args.length_mi or args.length_km
local width = args.width_mi and 1.60934*args.width_mi or args.width_km
local area = args.area_acre and 0.00404686*args.area_acre or
args.area_ha and 0.01*args.area_ha or
args.area_mi2 and 2.58999*args.area_mi2 or args.area_km2
local dim = computeDim(length, width, area)
return dim
end  
local function computeScale(args)
if args.scale then return args.scale end
local dim, units, scale
if args.dim then
dim, units = mw.ustring.match(args.dim,"^([-%d%.]+)%s*(%D*)")
args.units = units
args.default_viewport = 0.1 -- default geohack viewpoirt
scale = geohackDimToScale(dim, args)
end
if not scale then
dim = convertDim(args) or geohackTypeToDim(args)
args.units = 'km'
args.default_viewport = 0.2 --- when object dimensions or type is specified, assume 20cm viewport
scale = dim and geohackDimToScale(dim, args)
end
if not scale then return end
scale = math.floor(scale+0.5)
-- keep scale within sane bounds (OSM zoom levels 1-17)
if scale < 1600 then
scale = 1600
end
if scale > 200e6 then
scale = 200e6
end
return scale
end  
-- Argument checking
local positiveNumericArgs = {viewport_cm=true,viewport_px=true,length_mi=true,length_km=true,
width_mi=true,width_km=true,area_mi2=true,area_km2=true,
area_acre=true,area_ha=true,scale=true,population=true}  
local function cleanArgs(args)
local clean = {}
if type(args) == 'table' then
for k, v in pairs(args) do
if positiveNumericArgs[k] then
v = v and mw.ustring.gsub(v,",","") -- clean out any commas
v = tonumber(v) -- ensure argument is numeric
if v and v <= 0 then -- if non-positive, ignore value
v = nil
end
end
clean[k] = v
end
end
return clean
end  
-- Module entry points
function p._dim(args)
args = cleanArgs(args)
if args.dim then return args.dim end
-- compute scale for geohack
local scale = args.scale
local dim
if not scale then
args.default_viewport = 0.2 -- when specifying a object dimension or type, assume output spans 20cm
dim = convertDim(args) or geohackTypeToDim(args)
args.units = 'km'
scale = dim and geohackDimToScale(dim, args)
end
-- reset back to 10cm viewport for correct geohack dim output
args.viewport_cm = 10
dim = scale and geohackScaleToDim(scale, args)
return dim and tostring(math.floor(dim+0.5))..'km'
end  
function p._scale(args)
args = cleanArgs(args)
return computeScale(args)
end  
function p._zoom(args)
args = cleanArgs(args)
args.viewport_px = args.viewport_px or 200 --- viewport for Kartographer is high
local scale = computeScale(args)
if scale then
local zoom = geohackScaleToMapZoom(scale)
return zoom and math.floor(zoom)
end
end  
-- Template entry points
function p.dim
return p._dim(getArgs) or ''
end  
function p.scale
return p._scale(getArgs) or ''
end  
function p.zoom
return p._zoom(getArgs) or ''
end  
return p