[hibernate-dev] Coordinates storage in Lucene index for spatial functionality

[Emmanuel Bernard]

Let me see if I understood by rephrasing. I am trying to get a feel of where conversions happen.

I am assuming that this is mostly relevant for the boolean query approach and the later circle memory filtering (ie that quad tree is not involved).

Today we accept decimal coordinates from the user and store them as is in the index. But to calculate the right rectangle and then circle filter when 
we build a query and later filter elements in memory (circle): 

- we convert the query coordinates into radians to find the right box boundaries coordinates and convert them back into decimals
- for each matching element in the box we further convert the coordinates in radian to filter by circle

In the new scheme where radians are stored, we would:

- receive coordinates from the user as decimals
- convert them to radians once at indexing time and once at query time

So the big difference would be that we avoid the per element in the box filtering conversion from decimals to radians.

Am I correct or completely wrong?

On 3 mai 2012, at 10:12, Nicolas Helleringer wrote:

> Hi all,
> 
> Sanne and I have been wondering about the way the spatial
> branch/module/functionality for Hibernate Search shall store its
> coordinates in the Lucene index.
> 
> Today it is implemented with decimal degree for :
> - easy debugging/readability
> - ease of conversion on storage as we want to accept mainly decimal degree
> from users data
> 
> Sanne pointed out that when the search is done there is quite a few
> conversion to radians for distance calculation and suggested that we may
> store directly coordinates under their radians form.
> 
> I have tried a patch to implement this and as I was coding it I feel that
> the code was less readable, in the coordinates normalisation mainly and
> that there was as many conversion as before.
> Conversions had moved from search to import / export of coordinates in and
> out the spatial module scope to user scope.
> 
> What the docs does not tell (yet), is that we are waiting for WGS 84 (this
> is a coordinate system) decimal degree coordinates input, as these are
> quite a de facto standard (GPS output this way).
> 
> Today this is not the purpose of Hibernate Search spatial initiative to
> handle projections. There are opensource libs to handle that on user side
> very well (Proj4j)
> 
> So. The question is : shall we store as radians or decimal degree ?
> 
> Niko
> 
> P.S : Hope it is clear. If not ask for more.
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