[Haskell-cafe] Where am I going wrong with my bounding box function?
Michael Litchard
michael at schmong.org
Mon Jun 20 21:52:32 UTC 2016
I am writing a bounding box module for the octree
<https://github.com/BioHaskell/octree/tree/master> library. You can find my
branch here <https://github.com/mlitchard/octree/tree/MBB>. In the function
below, I try to make explicit the implicit bounding boxes of an Octree. The
problem is, not all bounding boxes are valid.
This is the function in question, followed by a way to replicate the
problem in ghci.
explicateMBB :: (BBox3, Octree a) -> [BBox3]
explicateMBB (mbb, (Leaf _)) = [mbb]
explicateMBB (mbb, (Node { split = split',
nwu = nwu',
nwd = nwd',
neu = neu',
ned = ned',
swu = swu',
swd = swd',
seu = seu',
sed = sed'
})) =
mbb:concatMap explicateMBB octList
where
octList = zip boxList children
boxList = [swdBox, sedBox, nwdBox, nedBox, swuBox, seuBox, nwuBox, neuBox]
children = [swd',sed',nwd',ned',swu',seu',nwu',neu']
swdBox = bound_corners swdCorner neuCorner
where
swdCorner = Vector3 (minX mbb) (minY mbb) (minZ mbb)
neuCorner = Vector3 (v3x split') (v3y split') (v3z split')
sedBox = bound_corners swdCorner neuCorner
where
swdCorner = Vector3 (v3x split') (minY mbb) (minZ mbb)
neuCorner = Vector3 (maxX mbb) (v3y split') (minZ mbb)
nwdBox = bound_corners swdCorner neuCorner
where
swdCorner = Vector3 (minX mbb) (v3y split') (minZ mbb)
neuCorner = Vector3 (v3x split') (maxY mbb) (v3z split')
nedBox = bound_corners swdCorner neuCorner
where
swdCorner = Vector3 (v3x split') (v3y split') (minZ mbb)
neuCorner = Vector3 (maxX mbb) (maxY mbb) (v3z split')
swuBox = bound_corners swdCorner neuCorner
where
swdCorner = Vector3 (minX mbb) (minY mbb) (v3z split')
neuCorner = Vector3 (v3x split') (v3y split') (maxZ mbb)
seuBox = bound_corners swdCorner neuCorner
where
swdCorner = Vector3 (v3x split') (minY mbb) (v3z split')
neuCorner = Vector3 (maxX mbb) (v3y split') (maxZ mbb)
nwuBox = bound_corners swdCorner neuCorner
where
swdCorner = Vector3 (minX mbb) (v3y split') (v3z split')
neuCorner = Vector3 (v3x split') (maxY mbb) (maxZ mbb)
neuBox = bound_corners swdCorner neuCorner
where
swdCorner = Vector3 (v3x split') (v3y split') (v3z split')
neuCorner = Vector3 (maxX mbb) (maxY mbb) (maxZ mbb)
To replicate problem:
git clone https://github.com/mlitchard/octree.git
git checkout MBB
stack ghci
In ghci, do the following :
:m + Data.List Data.Vector.Class System.Random System.Random.Shuffle
Data.BoundingBox.B3
let infinity = (read "Infinity") :: Double
let swdCorner = Vector3 (-infinity) (-infinity) (-infinity)
let neuCorner = Vector3 (infinity) (infinity) (infinity)
let rbb = bound_corners swdCorner neuCorner
xGen <- getStdGen
yGen <- newStdGen
zGen <- newStdGen
let xPoints = shuffle' [-256 .. 256] 513 xGen
let yPoints = shuffle' [-256 .. 256] 513 yGen
let zPoints = shuffle' [-256 .. 256] 513 zGen
let xPoints' = map fromInteger xPoints :: [Double]
let yPoints' = map fromInteger yPoints :: [Double]
let zPoints' = map fromInteger zPoints :: [Double]
let tup513 = zip3 xPoints' yPoints' zPoints'
let construct_vect = (\(x,y,z) -> Vector3 x y z)
let vect513 = map construct_vect tup513
let pre_oct513 = zip vect513 [1 .. 513]
let octree513 = fromList pre_oct513
length $ filter (== False) $ map isValidMBB $ explicateMBB (rbb,octree513)
The answer will be 9, but should be 0.
I feel like one of the fooBox where clauses is wrong, but I have gone over
each one several times, and I am not seeing which one it is.
If you needed a visual aid like I did, I found this pic
<https://geidav.files.wordpress.com/2014/08/full_octree.png?w=820> to be
helpful. My sample does 2 subdivisions.
Any insight into what is going wrong would be appreciated.
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