Spatio-temporal Range Query

Extensible operations

Operations in ST-Hadoop are implemented as regular MapReduce programs. The main difference between spatio-temporal operations and spatial operations shipped with SpatialHadoop is that the input file is spatiotemporally indexed. To read a spatio-temporal indexed file, you need to provide the correct ShapeFormat that represent an extension of STPoint. Besides, the regular map and reduce functions, ST-Hadoop allows you to provide a filter function that performs and early pruning step that prunes away file blocks that do not contribute to the final answer based on two property their minimal bounding rectangles (MBRs) and their slicing time span (interval). In this tutorial, you will learn how to use built-in spatio-temporal range query and a step by step instructions on how to write your own spatio-temporal operation.


Spatio-temporal Range Query:

The basic operation of spatio-temporal data is the range query. The range query contains a set of shapes,  a rectangular query area (A), and an interval of the query time range (T). The output is all shapes that overlap with the query area (A) and time interval (T).
To use spatio-temporal range query you can execute the following command line. 
./hadoop jar st-hadoop-uber.jar strangequery 

/indexDir/ /Result 

rect:x1,y1,x2,y2 interval:t1,t2 

shape:edu.umn.cs.sthadoop.core.STPoint  -overwrite 


Parameters and Command Description
strangequery This is the map reduce method that invokes the spatio-temporal range query. 

The HDFS directory where the dataset is being indexed.

The directory represent the parent directory of the hierarchy spatio-temporal index

Result The HDFS output directory where the result will be stored. 
rect: The spatial minimum boundary rectangle area of the spatio-temporal range query. 
interval: The time interval of the spatio-temporal range query. The time should be in the following standard time format: yyyy-MM-dd, such as 2017-01-12.
shape: The shape format of should be extended from STPoint that support spatio-temporal data.

* Optional parameters to intentionally specify a specific resolution layer to query from. For example, if space partitioning technique used in spatio-temporal index then these possible parameters could be passed [ day, week, month, year] 

If property not specified in the execution command line, then ST-Hadoop will decide the execution plan considering all spatio-temporal resolution indices.

-overwrite This flag indicate to overwrite the output directory if it existed. 



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