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