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[task #15713] Make quad structure to make unique hashes of 4 objects
From: |
Mohammad Akhlaghi |
Subject: |
[task #15713] Make quad structure to make unique hashes of 4 objects |
Date: |
Mon, 6 Jul 2020 13:25:05 -0400 (EDT) |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0 |
Follow-up Comment #4, task #15713 (project gnuastro):
Very good! But just one thing: probably using the 3 nearest neighbors isn't
too good (there will be too many repetitions and thus too few quads for the
fit).
Maybe a better way to select the three neighbors would be this: let's assume
the healpix size is 'h' degrees. Look in a circle of radius of 'h' degrees
around each point sort them by distance, so the series of points becomes (p[0]
is the nearest, p[n] i the farthest):
p[0], p[1], ... p[n-4], p[n-3], p[n-2], p[n-1], p[n]
Then select p[n], p[n-2], p[n-4] as the other three points for constructing
the quad.
I feel this will create less repetition between the quads (since the
probability that they be the same is much less than the 3 nearest neighbors).
This method has the advantage that the quads will be large (on a scale of the
healpix), thus decreasing statistical errors.
It will thus be a little more computationally expensive, but I think it will
be worth it. To fix the computational cost when there are many points within
the circle of radius 'h', it may be possible to exploit the kd-tree to find
these points instead of actually sorting them. Or we can simply discard many
of the points closer than 'h/2'.
Another method (that is still seems to be more robust than the three nearest
neighbors) is to randomly select three points from all the points within a
distance of 'h'.
What do you think?
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- [task #15713] Make quad structure to make unique hashes of 4 objects, Sachin Kumar Singh, 2020/07/05
- [task #15713] Make quad structure to make unique hashes of 4 objects, Mohammad Akhlaghi, 2020/07/05
- [task #15713] Make quad structure to make unique hashes of 4 objects, Sachin Kumar Singh, 2020/07/06
- [task #15713] Make quad structure to make unique hashes of 4 objects,
Mohammad Akhlaghi <=
- [task #15713] Make quad structure to make unique hashes of 4 objects, Mohammad Akhlaghi, 2020/07/06
- [task #15713] Make quad structure to make unique hashes of 4 objects, Sachin Kumar Singh, 2020/07/06
- [task #15713] Make quad structure to make unique hashes of 4 objects, Mohammad Akhlaghi, 2020/07/06
- [task #15713] Make quad structure to make unique hashes of 4 objects, Sachin Kumar Singh, 2020/07/10
- [task #15713] Make quad structure to make unique hashes of 4 objects, Mohammad Akhlaghi, 2020/07/10
- [task #15713] Make quad structure to make unique hashes of 4 objects, Sachin Kumar Singh, 2020/07/11
- [task #15713] Make quad structure to make unique hashes of 4 objects, Raul Infante-Sainz, 2020/07/14
- [task #15713] Make quad structure to make unique hashes of 4 objects, Sachin Kumar Singh, 2020/07/14
- [task #15713] Make quad structure to make unique hashes of 4 objects, Sachin Kumar Singh, 2020/07/14
- [task #15713] Make quad structure to make unique hashes of 4 objects, Mohammad Akhlaghi, 2020/07/15