Efficient, database-independent PHP implementation of geospatial index? Zend_Search_Lucene extension?

I'm storing lat/lon information in a MySQL database, which doesn't have great geospatial search support. I'm already maintaining a separate Lucene text search index for efficient full text search, so I looked at the geospatial extension for Lucene; but it only seems to be available for the Java implementation, not the Zend_Search_Lucene PHP version I use.

Is there something similar that would allow me to maintain a separate, database-independent geospatial index? A good implementation of an R-Tree variant in PHP or something similar? A geospatial extension for Zend_Search_Lucene?

It'd need to allow efficient geospatial queries, mostly within-radius-of-x and within-bounding-box开发者_运维技巧-y queries, and return the id of the entry in the database.

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http://www.ideacode.com/content/spatial-searches-with-zendsearchlucene helped me in this situation