Spatial Search

Solr支援在地理空間搜尋中使用位置資料，使用空間搜尋，你可以：

• 索引點或者其他形狀
• 通過矩形框，圓或者其他形狀來過濾搜尋結果
• 通過點之間的距離 或者兩個區域之間的矩形之間的距離，排序或者增強分數
• 產生一個二維的網格來生成熱力圖或者點繪製

有四個欄位型別來進行空間搜尋：

• LatLonPointSpatialField
• LatLonType (已經過期)
• SpatialRecursivePrefixTreeFieldType (簡稱RPT )，包括RptWithGeometrySpatialField
• BBoxField

LatLonPointSpatialField 是一般點位搜尋的最常用的型別。它替代了 LatLonType ,為了相容LatLonType 還會存在。RPT提供了具有一些高階的特點，例如使用多邊形和熱力圖。
RptWithGeometrySpatialField 用來索引和檢索非點位資料，儘管它也可以辦到。它不可以進行排序和增強。
BBoxField是進行盒子索引，通過盒子查詢 ，制定具體的操作(Intersects,Within,Contains,Disjoint,Equals),或者相關的排序、增強比如overlapRatio或者區域。
一些深奧的詳細情況可以在下面連結中找到

LatLonPointSpatialField

下面是LatLonPointSpatialField 在Schema中如何配置：

<fieldType name="location" class="solr.LatLonPointSpatialField" docValues="true"/>

LLPSF支援在 indexed, stored, docValues, 和multiValued的切換。 LLPSF 內部使用 Lucene “Points” 進行索引. 當啟用”docValues” 的時候, 經度和緯度位元交織為64位，存入Lucene DocValues中。docValues 資料精度達到釐米級。

Indexing Points

為了索引大地點（經度和緯度），需要以這樣的格式”lat,lon”提供。
所以非大地點位，需要看情況。RPT使用”x y”（空格分隔），PointType 然而使用”x,y” (逗號分隔)。
如果你寧願使用工業標準的格式， Solr 支援 WKT 和GeoJSON。然而對於簡單的資料，它們過於笨重。 (過期的型別 LatLonType 或者PointType並不支援)。

Searching with Query Parsers

Solr中存在兩個空間搜尋查詢解析器: geofilt 和bbox。 它們接收以下引數:

geofilt

The geofilt filter allows you to retrieve results based on the geospatial distance (AKA the “great circle distance”) from a given point. Another way of looking at it is that it creates a circular shape filter. For example, to find all documents within five kilometers of a given lat/lon point, you could enter &q=:&fq={!geofilt sfield=store}&pt=45.15,-93.85&d=5. This filter returns all results within a circle of the given radius around the initial point:

bbox

The bbox filter is very similar to geofilt except it uses the bounding box of the calculated circle. See the blue box in the diagram below. It takes the same parameters as geofilt. Here’s a sample query: &q=:&fq={!bbox sfield=store}&pt=45.15,-93.85&d=5. The rectangular shape is faster to compute and so it’s sometimes used as an alternative to geofilt when it’s acceptable to return points outside of the radius. However, if the ideal goal is a circle but you want it to run faster, then instead consider using the RPT field and try a large “distErrPct” value like 0.1 (10% radius). This will return results outside the radius but it will do so somewhat uniformly around the shape.

Filtering by an arbitrary rectangle

Sometimes the spatial search requirement calls for finding everything in a rectangular area, such as the area covered by a map the user is looking at. For this case, geofilt and bbox won’t cut it. This is somewhat of a trick, but you can use Solr’s range query syntax for this by supplying the lower-left corner as the start of the range and the upper-right corner as the end of the range. Here’s an example: &q=:&fq=store:[45,-94 TO 46,-93]. LatLonType (deprecated) does not support rectangles that cross the dateline. For RPT and BBoxField, if you are non-geospatial coordinates (geo=”false”) then you must quote the points due to the space, e.g. “x y”.

Optimizing: Cache or Not

It’s most common to put a spatial query into an “fq” parameter – a filter query. By default, Solr will cache the query in the filter cache. If you know the filter query (be it spatial or not) is fairly unique and not likely to get a cache hit then specify cache=”false” as a local-param as seen in the following example. The only spatial types which stand to benefit from this technique are LatLonPointSpatialField and LatLonType (deprecated). Enable docValues on the field (if it isn’t already). LatLonType (deprecated) additionally requires a cost=”100” (or more) local-param.
&q=…mykeywords…&fq=…someotherfilters…&fq={!geofilt cache=false}&sfield=store&pt=45.15,-93.85&d=5
LLPSF does not support Solr’s “PostFilter”.

Distance Sorting or Boosting (Function Queries)

There are four distance function queries: geodist, see below, usually the most appropriate; dist , to calculate the p-norm distance between multi-dimensional vectors; hsin , to calculate the distance between two points on a sphere; and sqedist , to calculate the squared Euclidean distance between two points. For more information about these function queries, see the section on Function Queries.

geodist

geodist is a distance function that takes three optional parameters: (sfield,latitude,longitude). You can use the geodist function to sort results by distance or score return results.
For example, to sort your results by ascending distance, enter …&q=:&fq={!geofilt}&sfield=store&pt=45.15,-93.85&d=50&sort=geodist() asc.
To return the distance as the document score, enter …&q={!func}geodist()&sfield=store&pt=45.15,-93.85&sort=score+asc.

More Examples

Here are a few more useful examples of what you can do with spatial search in Solr.

Use as a Sub-Query to Expand Search Results

Here we will query for results in Jacksonville, Florida, or within 50 kilometers of 45.15,-93.85 (near Buffalo, Minnesota):
&q=:&fq=(state:”FL” AND city:”Jacksonville”) OR {!geofilt}&sfield=store&pt=45.15,-93.85&d=50&sort=geodist()+asc

Facet by Distance

To facet by distance, you can use the Frange query parser:
&q=:&sfield=store&pt=45.15,-93.85&facet.query={!frange l=0 u=5}geodist()&facet.query={!frange l=5.001 u=3000}geodist()
There are other ways to do it too, like using a {!geofilt} in each facet.query.

Boost Nearest Results

Using the DisMax or Extended DisMax, you can combine spatial search with the boost function to boost the nearest results:
&q.alt=:&fq={!geofilt}&sfield=store&pt=45.15,-93.85&d=50&bf=recip(geodist(),2,200,20)&sort=score desc