Class PrefixTreeStrategy

An abstract SpatialStrategy based on SpatialPrefixTree. The two subclasses are RecursivePrefixTreeStrategy and TermQueryPrefixTreeStrategy. This strategy is most effective as a fast approximate spatial search filter.

Characteristics:

  • Can index any shape; however only RecursivePrefixTreeStrategy can effectively search non-point shapes.
  • Can index a variable number of shapes per field value. This strategy can do it via multiple calls to CreateIndexableFields(IShape) for a document or by giving it some sort of Shape aggregate (e.g. NTS WKT MultiPoint). The shape's boundary is approximated to a grid precision.
  • Can query with any shape. The shape's boundary is approximated to a grid precision.
  • Only Intersects is supported. If only points are indexed then this is effectively equivalent to IsWithin.
  • The strategy supports MakeDistanceValueSource(IPoint, Double) even for multi-valued data, so long as the indexed data is all points; the behavior is undefined otherwise. However, it will likely be removed in the future in lieu of using another strategy with a more scalable implementation. Use of this call is the only circumstance in which a cache is used. The cache is simple but as such it doesn't scale to large numbers of points nor is it real-time-search friendly.

Implementation:

The SpatialPrefixTree does most of the work, for example returning a list of terms representing grids of various sizes for a supplied shape. An important configuration item is DistErrPct which balances shape precision against scalability. See those docs.

This is a Lucene.NET INTERNAL API, use at your own risk
Inheritance
System.Object
SpatialStrategy
PrefixTreeStrategy
RecursivePrefixTreeStrategy
TermQueryPrefixTreeStrategy
Inherited Members
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
Namespace: Lucene.Net.Spatial.Prefix
Assembly: Lucene.Net.Spatial.dll
Syntax
public abstract class PrefixTreeStrategy : SpatialStrategy

Constructors

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PrefixTreeStrategy(SpatialPrefixTree, String, Boolean)

Declaration
public PrefixTreeStrategy(SpatialPrefixTree grid, string fieldName, bool simplifyIndexedCells)
Parameters
Type Name Description
SpatialPrefixTree grid
System.String fieldName
System.Boolean simplifyIndexedCells

Fields

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FIELD_TYPE

Indexed, tokenized, not stored.

Declaration
public static readonly FieldType FIELD_TYPE
Field Value
Type Description
Lucene.Net.Documents.FieldType
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m_defaultFieldValuesArrayLen

Declaration
protected int m_defaultFieldValuesArrayLen
Field Value
Type Description
System.Int32
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m_distErrPct

Declaration
protected double m_distErrPct
Field Value
Type Description
System.Double
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m_grid

Declaration
protected readonly SpatialPrefixTree m_grid
Field Value
Type Description
SpatialPrefixTree
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m_simplifyIndexedCells

Declaration
protected readonly bool m_simplifyIndexedCells
Field Value
Type Description
System.Boolean

Properties

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DefaultFieldValuesArrayLen

A memory hint used by MakeDistanceValueSource(IPoint) for how big the initial size of each Document's array should be. The default is 2. Set this to slightly more than the default expected number of points per document.

Declaration
public virtual int DefaultFieldValuesArrayLen { get; set; }
Property Value
Type Description
System.Int32
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DistErrPct

The default measure of shape precision affecting shapes at index and query times.

Declaration
public virtual double DistErrPct { get; set; }
Property Value
Type Description
System.Double
Remarks

The default measure of shape precision affecting shapes at index and query times. Points don't use this as they are always indexed at the configured maximum precision (MaxLevels); this applies to all other shapes. Specific shapes at index and query time can use something different than this default value. If you don't set a default then the default is DEFAULT_DISTERRPCT -- 2.5%.

See Also
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Grid

Declaration
public virtual SpatialPrefixTree Grid { get; }
Property Value
Type Description
SpatialPrefixTree

Methods

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CreateIndexableFields(IShape)

Declaration
public override Field[] CreateIndexableFields(IShape shape)
Parameters
Type Name Description
Spatial4n.Core.Shapes.IShape shape
Returns
Type Description
Field[]
Overrides
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CreateIndexableFields(IShape, Double)

Declaration
public virtual Field[] CreateIndexableFields(IShape shape, double distErr)
Parameters
Type Name Description
Spatial4n.Core.Shapes.IShape shape
System.Double distErr
Returns
Type Description
Field[]
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MakeDistanceValueSource(IPoint, Double)

Declaration
public override ValueSource MakeDistanceValueSource(IPoint queryPoint, double multiplier)
Parameters
Type Name Description
Spatial4n.Core.Shapes.IPoint queryPoint
System.Double multiplier
Returns
Type Description
Lucene.Net.Queries.Function.ValueSource
Overrides