anchor.diff:  WKT can also describe coordinate reference systems (CRS) and projections. 
   One common source of confusing is that, by default, the X-coordinate (longitude)is followed by Y-coordinate (latitude) 
   while many people are used to the Y-X (latitude-longitude) notation.
  -
  -=== Reading WKT Literals
  -
  -=== Writing WKT Literals
  -
  -RDF4j 2.1.x uses Spatial4J 0.4.1, which does not support writing shapes to WKT just yet (added in 0.5).
  -
  -An extremely simple writer could look like:
  -
  -[source,java]
  -----
  -public static String toWkt(Point p) {
  -   return "POINT(" + p.getX() + " " + p.getY() + ")";
  -}
  -----
  -
  -== Queries
  -
  -=== Simple shapes
   
   Spatial4j provides some convenience functions for generating simple geometric shapes.
   For instance, points representing the center of the cities of Amsterdam, Brussels... can easily be generated using `SpatialContext.GEO`.
  
positive.code: ----
  
  Circles and rectangles are also supported, polygons require JTS to be present.
  
  === Distance query
  
  
negative.code: = GeoSPARQL
  
  == SAILs, relation with Spatial4j / JTS
  
  Most of the geo heavy-lifting is performed by the SAILs, which also means that GeoSPARQL support (or lack thereof) depends on the SAIL being used.
  Strictly speaking using a (text) search engine like Lucene is not required, but it will speed up spatial queries.
  
  === Lucene
  
  By default, the Lucene SAIL only spatially indexes `http://www.opengis.net/ont/geosparql#asWKT` fields.
  This can be changed using the `LuceneSail.WKT_FIELDS` parameter.
  
  The Lucene SAIL included in RDF4j uses a slightly outdated version of the https://www.locationtech.org/proposals/spatial4j[Spatial4j] library, 
  which in turn relies on an older version of the https://www.locationtech.org/projects/technology.jts[JTS] library for certain features.
  This JTS library is not bundled with RDF4j due to license issues.
  Future versions of RDF4j will likely solve this issue, as both Spatial4j and JTS are moving to https://www.locationtech.org[Eclipse LocationTech],
  and the JTS license will be changed.
  
  Meanwhile RDF4j users can use the Solr or ElasticSearch SAIL to connect to external search services.
  
  === Providing your own SpatialSupportInitializer
  
  Another option is to implement a class `org.eclipse.rdf4j.query.algebra.evaluation.function.geosparql.SpatialSupportInitializer`.
  For example, https://bitbucket.org/pulquero/sesame-geosparql-jts[Mark Hale's sesame-geosparql-jts].
  
  == WKT Literals
  
  