After having spent a lot of time looking at the Tier stuff and debugging it and 
discussing it on IRC, I am of the opinion (and, I still have some belief that 
it's just me who isn't getting it, but others have confirmed my suspicion) that 
the spatial Cartesian Tier implementation is broken and, due to the lack of 
documentation and resources, it is not clear how to fix it; furthermore we 
don't seem to have anyone with the bandwidth or interest to fix it (I've tried, 
but I've about reached my limit on it in terms of willingness to work on it).  
Even if it is not broken and it is just me, the fact that I don't get it after 
spending as much time on it that I have is not a good sign for maintainability. 
 

AFAICT, a lot of it stems from the fact that SinusoidalProjection is broken 
(https://issues.apache.org/jira/browse/LUCENE-2519) and then layers upon layers 
of other, minor issues were built on top of that such that at the end of those 
layers are unit tests that are nearly impossible to untangle and in between is 
a fairly large mess.   Well, I suppose I should moderate those statements: I 
think all of it probably works as long as you stay completely in a given 
quadrant of the Earth for all your points (and likely really, just the US/ 
northern/western hemispheres), but even then it only works b/c it consistently 
calculates the wrong values for all points.

At the same time, I think the theory behind it (i.e. a labeled, nested grid 
system) is useful for many people solving spatial search problems and can offer 
significant query time savings.  So, I think there are a couple of things we 
could do:

1. Remove it and start from scratch and take a more standard approach
2. Find someone to fix the existing stuff who groks it
3. Document that it is only really useful for a given quadrant and then either 
do 1 or 2 over the long term.  We still need to fix somethings, IMO, to feel 
comfortable w/ it.
4. At a minimum, I think we should mark it as deprecated until it can be better 
dealt with later

For now, I'm going to remove it from Solr and just focus on finishing up the 
filtering stuff for the other point types.

Thoughts?  Volunteers?

-Grant



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