org.apache.lucene.spatial

## Class SpatialStrategy

- java.lang.Object
- - org.apache.lucene.spatial.SpatialStrategy

Direct Known Subclasses:
  PointVectorStrategy, PrefixTreeStrategy

    public abstract class SpatialStrategy
    extends Object

The SpatialStrategy encapsulates an approach to indexing and searching based on shapes.

Different implementations will support different features. A strategy should document these common elements:

- Can it index more than one shape per field?
- What types of shapes can be indexed?
- What types of query shapes can be used?
- What types of query operations are supported? This might vary per shape.
- Does it use the `FieldCache`, or some other type of cache? When?

If a strategy only supports certain shapes at index or query time, then in general it will throw an exception if given an incompatible one. It will not be coerced into compatibility.

Note that a SpatialStrategy is not involved with the Lucene stored field values of shapes, which is immaterial to indexing & search.

Thread-safe.

WARNING: This API is experimental and might change in incompatible ways in the next release.

### Field Summary

Fields
`protected com.spatial4j.core.context.SpatialContext` `ctx`

### Constructor Summary

Constructors
Constructor and Description
`SpatialStrategy(com.spatial4j.core.context.SpatialContext ctx, String fieldName)` Constructs the spatial strategy with its mandatory arguments.

### Method Summary

Methods
`abstract Field[]` `createIndexableFields(com.spatial4j.core.shape.Shape shape)` Returns the IndexableField(s) from the `shape` that are to be added to the `Document`.
`String` `getFieldName()` The name of the field or the prefix of them if there are multiple fields needed internally.
`com.spatial4j.core.context.SpatialContext` `getSpatialContext()`
`abstract ValueSource` `makeDistanceValueSource(com.spatial4j.core.shape.Point queryPoint)` Make a ValueSource returning the distance between the center of the indexed shape and `queryPoint`.
`abstract Filter` `makeFilter(SpatialArgs args)` Make a Filter based principally on `SpatialOperation` and `Shape` from the supplied `args`.
`Query` `makeQuery(SpatialArgs args)` Make a Query based principally on `SpatialOperation` and `Shape` from the supplied `args`.
`ValueSource` `makeRecipDistanceValueSource(com.spatial4j.core.shape.Shape queryShape)` Returns a ValueSource with values ranging from 1 to 0, depending inversely on the distance from `makeDistanceValueSource(com.spatial4j.core.shape.Point)`.
`String` `toString()`

### Methods inherited from class java.lang.Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

### Field Detail

#### ctx

    protected final com.spatial4j.core.context.SpatialContext ctx

### Constructor Detail

#### SpatialStrategy

    public SpatialStrategy(com.spatial4j.core.context.SpatialContext ctx,
                   String fieldName)

Constructs the spatial strategy with its mandatory arguments.

### Method Detail

#### getSpatialContext

    public com.spatial4j.core.context.SpatialContext getSpatialContext()

#### getFieldName

    public String getFieldName()

The name of the field or the prefix of them if there are multiple fields needed internally.

Returns:
  Not null.

#### createIndexableFields

    public abstract Field[] createIndexableFields(com.spatial4j.core.shape.Shape shape)

Returns the IndexableField(s) from the `shape` that are to be added to the `Document`. These fields are expected to be marked as indexed and not stored.

Note: If you want to store the shape as a string for retrieval in search results, you could add it like this:

    document.add(new StoredField(fieldName,ctx.toString(shape)));

The particular string representation used doesn't matter to the Strategy since it doesn't use it.

Returns:
  Not null nor will it have null elements.
Throws:
  `UnsupportedOperationException` - if given a shape incompatible with the strategy

#### makeDistanceValueSource

    public abstract ValueSource makeDistanceValueSource(com.spatial4j.core.shape.Point queryPoint)

Make a ValueSource returning the distance between the center of the indexed shape and `queryPoint`. If there are multiple indexed shapes then the closest one is chosen.

#### makeQuery

    public Query makeQuery(SpatialArgs args)

Make a Query based principally on `SpatialOperation` and `Shape` from the supplied `args`. The default implementation is

    return new ConstantScoreQuery(makeFilter(args));

Throws:
  `UnsupportedOperationException` - If the strategy does not support the shape in `args`
  `UnsupportedSpatialOperation` - If the strategy does not support the `SpatialOperation` in `args`.

#### makeFilter

    public abstract Filter makeFilter(SpatialArgs args)

Make a Filter based principally on `SpatialOperation` and `Shape` from the supplied `args`.

If a subclasses implements `makeQuery(org.apache.lucene.spatial.query.SpatialArgs)` then this method could be simply:

    return new QueryWrapperFilter(makeQuery(args).getQuery());

Throws:
  `UnsupportedOperationException` - If the strategy does not support the shape in `args`
  `UnsupportedSpatialOperation` - If the strategy does not support the `SpatialOperation` in `args`.

#### makeRecipDistanceValueSource

    public final ValueSource makeRecipDistanceValueSource(com.spatial4j.core.shape.Shape queryShape)

Returns a ValueSource with values ranging from 1 to 0, depending inversely on the distance from `makeDistanceValueSource(com.spatial4j.core.shape.Point)`. The formula is `c/(d + c)` where 'd' is the distance and 'c' is one tenth the distance to the farthest edge from the center. Thus the scores will be 1 for indexed points at the center of the query shape and as low as ~0.1 at its furthest edges.

#### toString

    public String toString()

Overrides:
  `toString` in class `Object`