NahSpark

OVERVIEW

NahSpark (Needle and Hand Spark) is a set of spatiotemporal Spark extensions implemented with optimizations for reading dataframes from NahFS.

COMMANDS

SPARK SHELL (SQL)

// dataframe operations
df.select("_c0").show()
df.filter($"_c1" > 100).show()
df.groupBy("_c2").count().show()

// rename columns
val lookupMap = Map("_c0" -> "latitude",
    "_c1" -> "longitude", "_c3" -> "timestamp")
val named_df = lookupMap.foldLeft(df)(
    (acc, ca) => acc.withColumnRenamed(ca._1, ca._2))

SPATIAL JOINS

geospark

core/src/main/java/org/datasyslab/geospark/spatialOperator/JoinQuery.java core/src/main/java/org/datasyslab/geospark/joinJudgement/JudgementBase.java

// initialize leftRDD val leftRDD = new PointRDD(sc, points, FileDataSplitter.CSV, false, numPartitions, StorageLevel.MEMORY_ONLY) leftRDD.spatialPartitioning(partitioningScheme) leftRDD.buildIndex(idx,true) leftRDD.indexedRDD.persist(StorageLevel.MEMORY_ONLY) leftRDD.spatialPartitionedRDD.persist(StorageLevel.MEMORY_ONLY)

// redacted - same for rightRDD

count = JoinQuery.SpatialJoinQuery(leftRDD, rightRDD, true, false).count() // internally leftRdd.spatialRDD.zipPartitions(rightRDD.indexedRDD, judgement) -- or something like this // judgement is an iterator over the RDD's -- optimally assumes spatially sorted RDD // judgements may be for an indexed leftRDD, indexed rightRDD, or neither

REFERENCES

• https://github.com/locationtech/jts
  • https://locationtech.github.io/jts/javadoc/
• https://github.com/EsotericSoftware/kryo
  • https://github.com/eishay/jvm-serializers/wiki
• https://jaceklaskowski.gitbooks.io/mastering-spark-sql/spark-sql-udfs.html
  • https://jaceklaskowski.gitbooks.io/mastering-spark-sql/spark-sql-PartitionedFile.html
• https://datasystemslab.github.io/GeoSpark/tutorial/sql/
• http://blog.madhukaraphatak.com/introduction-to-spark-two-part-6/

TODO

• implement spatial joins
• support timestamp queries