A question about the z_order.py

[Exbilar]

Hey there, thanks for your great contribution. I am reading the code about serialization, and I found the code snipt here in z_order.py:

    def xyz2key(self, x, y, z, depth):
        key = torch.zeros_like(x)
        for i in range(depth):
            mask = 1 << i
            key = (
                key
                | ((x & mask) << (2 * i + 2))
                | ((y & mask) << (2 * i + 1))
                | ((z & mask) << (2 * i + 0))
            )
        return key

I am confused why you are using 2 * i here, and I suppose it might be 3 * i here. Thanks for your answering!

[ListIndexOutOfRange]

Hey,

I'm not the author of the code but I believe this function is correct. The variable i here loops through the bits, it must take successive power of two.

[Exbilar]

Hi,

Thanks for your answering! I am not very familiar with the z-ordering curve. My understanding is for coordinates (X,Y,Z)
X = (..., x2, x1, x0)
Y = (..., y2, y1, y0)
Z = (..., z2, x1, z0)

the encoded key value is Key = (..., x2, y2, z2, x1, y1, z1, x0, y0, z0)

So I suppose it is 3 * i here, or do I have mistaken somewhere?

[ListIndexOutOfRange]

No it doesn't work like that, it uses a binary representation. If you encode a point clouds (N, 3), the key is a sequence of N integers, each of them corresponding to the value of the interleaved bits. It leverages discretize 3D space and a specific ordering in order to assign a single integer to a 3D coordinate.

[Exbilar]

Forgive my poor writting, I mean the key = (..., x2, y2, z2, x1, y1, z1, x0, y0, z0) is a binary representation, while
X = (..., x2, x1, x0)
Y = (..., y2, y1, y0)
Z = (..., z2, x1, z0)
are the binary represention of X, Y, Z, they are all integers.