[postgis-users] Advice on space efficient grid indexing

[Arnaud L.]

Le 29/09/2016 à 10:59, Martijn Meijers a écrit :
> Would the idea of the Spatial Location Code help you?
> http://www.gdmc.nl/oosterom/slc.pdf


Hi Martijn,
thanks a lot for your answer.

That's quite a long read but it looks very interesting, I'll look at 
this tomorrow. Thanks in advance !

I have to mention that I made some progress in my quest by finding out 
about pairing functions. https://en.wikipedia.org/wiki/Pairing_function

I'll let you know how it went.

Regards
--
Arnaud





>
>
> Martijn
>
>
> On 29-09-16 10:49, Arnaud L. wrote:
>> Le 29/09/2016 à 10:11, Arnaud L. a écrit :
>>> What would be a more efficient way to store this cell coordinates so
>>> that disk usage would be limited and accessing the rows would be using
>>> the index efficiently ?
>>> Using a point geometry would not be space efficient I believe, and it
>>> seems overkill since we do not need to do any spatial operation on this
>>> column (only equality queries, i.e. retrieving all rows in a given
>>> cell).
>>> I also thought about a bigint array of two elements, but our database is
>>> mainly accessed through psqlodbc and I'm not sure that arrays are very
>>> efficient in this case.
>>
>> I should also have pointed out that there is a third parameter,
>> because we have two overlapping grids (but a given geomtry can only be
>> in one of them). Sot it is more a 3 columns reference than a 2 columns
>> one.
>> Also, the obvious choice of adding 3 columns (gridx, gridy, gridlevel)
>> would be that last choice, even after the ugly "char" column. We have
>> functions returning this "grid id", and it would be very inconvenient
>> if they should return setof bigints or records.
>> I really like the idea that a grid cell has a unique "id" that can be
>> easily computed, and that a geometry can be also easily retrieved from
>> this id with having to write complex sql like (gridx, gridy,
>> gridlevel) = (..., ..., ...).
>>
>> Regards
>> --
>> Arnaud
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>