[pgpointcloud] RLE and SIGBITS heuristics

[Oscar Martinez Rubi]

Hi,

About the XYZ binding for better compression. In our research in the NL 
escience center and TU Delft we have been thinking (not testing yet 
though) about one possible approach for this.

It is based on using space filling curves. So, once you have the points 
that go in a block you could compute the morton/hilbert code of the XYZ. 
Since all the points are close together such codes will be extremely 
similar, so one could store only the increments which could fit in many 
few bits. We have not tested or compared this with any of the other 
compressions but we just wanted to share it with you just in case you 
find it useful!

An additional improvement would be to sort the points within the blocks 
according to the morton code. Then, when doing crop/filter operations in 
the blocks one can use the morton codes for the queries similarly to 
what we presented in our papers with the flat table (without blocks), I 
attach one of them (see section 5.2). In a nutshell: You convert the 
query region into a set of quadtree/octree nodes which can be also 
converted to morton code ranges (thanks to relation between 
morton/hilbert curve and a quadtree/octree). You scale down the ranges 
to increments (like you did when storing the point of the block) and 
then you simply do range queries in sorted data with a binary algorithm. 
In this way you avoid the decompression of the morton code for most of 
the block. This filtering is equivalent to a bbox filter so it still 
requires a point in polygon check for some of the points.

Kind Regards,

Oscar.


On 16-04-15 18:15, Rémi Cura wrote:
> epic fail ! I had avoided html just for you
>
>    Dataset   |subset size  | compressing   | decompressing |
>              |(Million pts)|(Million pts/s)|(Million pts/s)|
> Lidar        |   473.3     |    4,49       |     4,67      |
> 21-atributes | 105.7     |    1,11       |     2,62      |
> Stereo   |    70       |    2,44       |     7,38      |
>
> Cheers
>
> 2015-04-16 17:42 GMT+02:00 Sandro Santilli <strk at keybit.net 
> <mailto:strk at keybit.net>>:
>
>     On Thu, Apr 16, 2015 at 05:30:12PM +0200, Rémi Cura wrote:
>     > OUps
>     >
>     > Dataset        |  subset size(Million pts) | compressing
>     (Million pts/s) |
>     > decompressing (Million pts/s)
>     > Lidar           |            473.3                |            
>      4,49
>     >               |             __4,67__
>     > 21 attributes |           105.7                 |
>     > 1,11                     |             2,62
>     > Stereo         |              70                  |            
>       2,44
>     >                |             7,38
>
>     These tables aren't really readable here.
>     Could you make sure to use a fixed-width font to write those tables
>     and to keep lines within 70 columns at most ?
>
>     --strk;
>
>
>
>
> _______________________________________________
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> pgpointcloud at lists.osgeo.org
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