diff --git a/polymer/eduke32/source/lunatic/build.lua b/polymer/eduke32/source/lunatic/build.lua
index 383e9b228..098308569 100644
--- a/polymer/eduke32/source/lunatic/build.lua
+++ b/polymer/eduke32/source/lunatic/build.lua
@@ -1,14 +1,14 @@
 
 -- Loaders for various BUILD structures for LuaJIT
 
--- TODO: bound-checking, load ART
-
 
 local ffi = require "ffi"
 local io = require "io"
 
+local error = error
 local assert = assert
 local print = print
+local setmetatable = setmetatable
 
 module(...)
 
@@ -62,6 +62,8 @@ local MAX =
     SECTORS = { [7]=1024, [8]=4096, [9]=4096 },
     WALLS = { [7]=8192, [8]=16384, [9]=16384 },
     SPRITES = { [7]=4096, [8]=16384, [9]=16384 },
+
+    TILES = 30720,
 }
 
 local function doread(fh, basectype, numelts)
@@ -85,6 +87,23 @@ local function doread(fh, basectype, numelts)
     return cd
 end
 
+local function set_secwalspr_mt(structar, maxidx)
+    local mt = {
+        __index = function(tab, idx)
+            if (idx < 0 or idx >= maxidx) then
+                error("Invalid structure array read access", 2)
+            end
+            return structar[idx]
+        end,
+
+        __newindex = function(tab, idx, newval)
+            error('cannot write directly to structure array', 2)
+        end,
+    }
+
+    return setmetatable({}, mt)
+end
+
 --== LOADBOARD ==--
 -- returns:
 --  on failure, nil, errmsg
@@ -133,6 +152,9 @@ function loadboard(filename)
 
     -- sectors
     map.numsectors = cd[2]
+    if (map.numsectors == nil) then
+        return nil, "Couldn't read number of sectors"
+    end
     if (map.numsectors <= 0 or map.numsectors > MAX.SECTORS[map.version]) then
         fh:close()
         return nil, "Invalid number of sectors"
@@ -145,6 +167,9 @@ function loadboard(filename)
 
     -- walls
     cd = doread(fh, "int16_t", 1)
+    if (cd == nil) then
+        return nil, "Couldn't read number of walls"
+    end
     map.numwalls = cd[0]
     if (map.numwalls <= 0 or map.numwalls > MAX.WALLS[map.version]) then
         fh:close()
@@ -158,6 +183,9 @@ function loadboard(filename)
 
     -- sprites
     cd = doread(fh, "int16_t", 1)
+    if (cd == nil) then
+        return nil, "Couldn't read number of sprites"
+    end
     map.numsprites = cd[0]
     if (map.numsprites < 0 or map.numsprites > MAX.SPRITES[map.version]) then
         fh:close()
@@ -169,7 +197,100 @@ function loadboard(filename)
         return nil, "Couldn't read sprites"
     end
 
+    map.sector = set_secwalspr_mt(map.sector, map.numsectors)
+    map.wall = set_secwalspr_mt(map.wall, map.numwalls)
+    map.sprite = set_secwalspr_mt(map.sprite, map.numsprites)
+
     -- done
     fh:close()
     return map
 end
+
+
+local function set_sizarray_mt(sizar)
+    local mt = {
+        __index = function(tab, idx)
+            if (idx < 0 or idx >= MAX.TILES) then
+                error("Invalid tile size array read access", 2)
+            end
+            return sizar[idx]
+        end,
+
+        __newindex = function(tab, idx, newval)
+            if (idx < 0 or idx >= MAX.TILES) then
+                error("Invalid tile size array write access", 2)
+            end
+            sizar[idx] = newval
+        end,
+    }
+
+    return setmetatable({}, mt)
+end
+
+
+--== LOADARTS (currently tilesizx and tilesizy only) ==--
+-- filenames: a table with ART file names
+-- returns:
+--  on failure, nil, errmsg
+--  on success, a table
+--    {
+--      sizx = <cdata (array of length MAXTILES)>
+--      sizy = <cdata (array of length MAXTILES)>
+--    }
+function loadarts(filenames)
+    local tile = {
+        sizx = ffi.new("int16_t [?]", MAX.TILES),
+        sizy = ffi.new("int16_t [?]", MAX.TILES),
+    }
+
+    for fni=1,#filenames do
+        local fn = filenames[fni]
+        local fh, errmsg = io.open(fn)
+
+        if (fh==nil) then
+            return nil, errmsg
+        end
+
+        local cd = doread(fh, "int32_t", 4)
+        -- artversion, numtiles, localtilestart, localtileend
+        if (cd==nil) then
+            fh:close()
+            return nil, fn..": Couldn't read header"
+        end
+
+        local localtilestart = cd[2]
+        local numtileshere = cd[3]-localtilestart
+
+        if (numtileshere < 0 or localtilestart+numtileshere >= MAX.TILES) then
+            fh:close()
+            return nil, fn..": Invalid tile start/end"
+        end
+
+        if (numtileshere==0) then
+            fh:close()
+        else
+            -- X sizes
+            cd = doread(fh, "int16_t", numtileshere)
+            if (cd == nil) then
+                fh:close()
+                return nil, fn..": Couldn't read tilesizx array"
+            end
+
+            ffi.copy(tile.sizx+localtilestart, cd, numtileshere*2)
+
+            -- Y sizes
+            cd = doread(fh, "int16_t", numtileshere)
+            if (cd == nil) then
+                fh:close()
+                return nil, fn..": Couldn't read tilesizy array"
+            end
+
+            ffi.copy(tile.sizy+localtilestart, cd, numtileshere*2)
+        end
+    end
+
+    tile.sizx = set_sizarray_mt(tile.sizx)
+    tile.sizy = set_sizarray_mt(tile.sizy)
+
+    return tile
+end
diff --git a/polymer/eduke32/source/lunatic/foreachmap.lua b/polymer/eduke32/source/lunatic/foreachmap.lua
index 52bb16f1c..c05b45416 100755
--- a/polymer/eduke32/source/lunatic/foreachmap.lua
+++ b/polymer/eduke32/source/lunatic/foreachmap.lua
@@ -4,23 +4,35 @@
 
 -- The first cmdline arg is a name of a lua file (may be sans .lua) which must
 -- be a module and is `require'd into this script, e.g. "stats" or "stats.lua".
--- Then, for each 2nd and following argument, if map loading succeeds,
--- .success(map, filename) is run, otherwise .failure(filename, errmsg) --
--- these must be functions in the loaded module.
+-- First, a key named .init is looked up in the loaded module and if it exists,
+-- it is run like .init(arg)  (thus allowing it to parse the command-line
+-- arguments and then potentially remove the ones it used).
+-- If .init returns non-nil, this script aborts.
+-- Otherwise, for each 2nd and following argument, if map loading succeeds,
+--  .success(map, filename) is run, otherwise
+--  .failure(filename, errmsg) is run if that key exists, or a standard error
+--  message is printed to stderr.
+-- Finally, if there is a .finish field in the module, it is run with no args.
 
--- TODO: aggregate batch mode
-
-
-if (#arg < 1) then
-    error("Usage: luajit ./foreachmap <module[.lua]> <filename.map> ...")
-end
 
 local B = require "build"
 local string = require "string"
+local io = require "io"
+local os = require "os"
+
+if (#arg < 1) then
+    io.stdout:write("Usage: luajit ./foreachmap <module[.lua]> [init args...] <filename.map> ...\n\n")
+    return
+end
 
 local modname = string.gsub(arg[1], "%.lua$", "")
 local mod = require(modname)
 
+if (mod.init) then
+    if (mod.init(arg) ~= nil) then
+        os.exit(1)
+    end
+end
 
 for i=2,#arg do
     local fn = arg[i]
@@ -29,6 +41,14 @@ for i=2,#arg do
     if (map ~= nil) then
         mod.success(map, fn)
     else
-        mod.failure(fn, errmsg)
+        if (mod.failure) then
+            mod.failure(fn, errmsg)
+        else
+            io.stderr:write(string.format("--- %s: %s\n", fn, errmsg))
+        end
     end
 end
+
+if (mod.finish) then
+    mod.finish()
+end
diff --git a/polymer/eduke32/source/lunatic/mapastats.lua b/polymer/eduke32/source/lunatic/mapastats.lua
new file mode 100644
index 000000000..493792a62
--- /dev/null
+++ b/polymer/eduke32/source/lunatic/mapastats.lua
@@ -0,0 +1,50 @@
+
+-- Print out some aggregate statistics for passed BUILD maps,
+-- foreachmap module.
+
+local string = require "string"
+local math = require "math"
+
+local print = print
+
+module(...)
+
+
+local function printf(fmt, ...)
+    print(string.format(fmt, ...))
+end
+
+
+local N = 0
+
+local sumnumsectors = 0
+local sumnumwalls = 0
+
+local sumratio = 0
+local sumsqratio = 0
+
+function success(map, fn)
+    local ns = map.numsectors
+    local nw = map.numwalls
+
+    N = N+1
+
+    sumratio = sumratio + nw/ns
+    sumsqratio = sumsqratio + (nw/ns)^2
+
+    sumnumsectors = sumnumsectors+ns
+    sumnumwalls = sumnumwalls+nw
+end
+
+function finish()
+    printf("%d maps\n", N)
+    printf("total sectors: %d", sumnumsectors)
+    printf("total walls: %d", sumnumwalls)
+    printf("total walls / total sectors: %.02f", sumnumwalls/sumnumsectors)
+    printf("")
+    printf("Walls/sector")
+
+    local meanwpers = sumratio/N
+    printf(" mean: %.02f", meanwpers)
+    printf(" stdev: %.02f", math.sqrt(sumsqratio/N - meanwpers^2))
+end
diff --git a/polymer/eduke32/source/lunatic/mapstats.lua b/polymer/eduke32/source/lunatic/mapstats.lua
index d68076fea..aa2127a62 100644
--- a/polymer/eduke32/source/lunatic/mapstats.lua
+++ b/polymer/eduke32/source/lunatic/mapstats.lua
@@ -19,8 +19,7 @@ function success(map, fn)
     printf("  version: %d", map.version)
     printf("  numsectors: %d\n  numwalls: %d\n  numsprites: %d",
            map.numsectors, map.numwalls, map.numsprites)
-end
-
-function failure(fn, errmsg)
-    printf("--- %s: %s", fn, errmsg)
+    printf("  walls/sector: %.02f\n  sprites/sector: %.02f",
+          map.numwalls/map.numsectors, map.numsprites/map.numsectors)
+    printf("")
 end
diff --git a/polymer/eduke32/source/lunatic/mapypan.lua b/polymer/eduke32/source/lunatic/mapypan.lua
new file mode 100644
index 000000000..0d4280655
--- /dev/null
+++ b/polymer/eduke32/source/lunatic/mapypan.lua
@@ -0,0 +1,164 @@
+
+-- Display information about problematic wall ypannings,
+-- foreachmap module.
+
+local string = require "string"
+local table = require "table"
+local bit = require "bit"
+
+local print = print
+local pairs = pairs
+local rawget = rawget
+local setmetatable = setmetatable
+
+local B = require "build"
+
+module(...)
+
+
+local function printf(fmt, ...)
+    print(string.format(fmt, ...))
+end
+
+
+local tile
+
+function init(arg)
+    local artargend = nil
+    for i=2,#arg do
+        if (arg[i]=="--") then
+            artargend = i
+            break
+        end
+    end
+
+    if (artargend==nil or artargend==0) then
+        printf("Usage: luajit ./foreachmap.lua <tilesXXX.ART> [, ...] -- <filename1.map> ...\n")
+        return 1
+    end
+
+    local artfns = {}
+    for i=2,artargend-1 do
+        artfns[#artfns+1] = arg[i]
+    end
+
+    local i = 2
+    local j = artargend+1
+
+    while (arg[j]) do
+        arg[i] = arg[j]
+        arg[j] = nil
+
+        i = i+1
+        j = j+1
+    end
+
+    local tile_, errmsg = B.loadarts(artfns)
+    if (tile_ == nil) then
+        printf("%s", errmsg)
+        return 2
+    end
+
+    tile = tile_  -- set 'tile' file-scope var
+end
+
+local table_default0_mt = {
+    __index = function(tab, idx)
+        if (rawget(tab, idx)==nil) then
+            return 0
+        end
+        return rawget(tab, idx)
+    end
+}
+
+
+local sector, wall, sprite
+
+function success(map, fn)
+    -- set file-scope vars for convenience
+    sector = map.sector
+    wall = map.wall
+    sprite = map.sprite
+
+    -- counts of non-pow2 tiles, per tilenum
+    local np2tile = setmetatable({}, table_default0_mt)
+    -- walls/overwall indices with non-pow2 tiles, [walidx]=true
+    local np2wall = {}
+    -- [i]=wallidx
+    local np2walls = {}
+
+    local badoverpicnum = false
+
+    for i=0,map.numsectors-1 do
+        local startwall = sector[i].wallptr
+        local endwall = startwall+sector[i].wallnum-1
+
+        for w=startwall,endwall do
+            for n=1,2 do
+                local pic, ysiz
+
+                if (wall[w].nextwall < 0) then
+                    -- We don't care for white walls
+                elseif (n==1) then
+                    pic = wall[w].picnum
+                    ysiz = tile.sizy[pic]
+                else
+                    pic = wall[w].overpicnum
+                    if (pic < 0 or pic > 30720) then  -- MAXTILES
+                        badoverpicnum = true
+                    else
+                        ysiz = tile.sizy[pic]
+
+                        if (bit.band(wall[w].cstat, 16+32)==0) then
+                            -- we don't care about non-masked/1-way walls
+                            ysiz = 0
+                        end
+                    end
+                end
+
+                if (ysiz~=nil and ysiz > 0 and bit.band(ysiz, bit.bnot(ysiz-1))~=ysiz) then
+                    -- non-pow2 ysize
+
+                    np2tile[pic] = np2tile[pic]+1
+
+                    if (not np2wall[w]) then
+                        np2wall[w] = true
+                        np2walls[#np2walls+1] = w
+                    end
+                end
+            end
+        end
+    end
+
+    -- report our findings
+
+    -- sort in wall index order
+    table.sort(np2walls)
+
+    printf("--- %s:", fn)
+
+--[[
+    printf(" Walls:")
+    for i=1,#np2walls do
+        printf("  %d", np2walls[i])
+    end
+    printf("")
+--]]
+    printf(" %d red walls with non-pow2 ysize tiles", #np2walls)
+    if (badoverpicnum) then
+        printf(" (some red walls have out-of-bounds overpicnums)")
+    end
+
+    local np2tiles = {}
+    for tilenum,_ in pairs(np2tile) do
+        np2tiles[#np2tiles+1] = tilenum
+    end
+    table.sort(np2tiles)
+
+    printf(" Tiles:")
+    for i=1,#np2tiles do
+        printf("  %d", np2tiles[i])
+    end
+
+    printf("")
+end