Package

geotrellis

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package geotrellis

Visibility
  1. Public
  2. All

Value Members

  1. package bench

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    Module utilities.

    Module utilities. Originally from geotrellis-benchmark

  2. package doc

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  3. package geomesa

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  4. package geotools

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  5. package macros

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  6. package proj4

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  7. package raster

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  8. package shapefile

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  9. package slick

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    Implicit conversion for geotrellis.vector.Geometry instances.

    Implicit conversion for geotrellis.vector.Geometry instances.

    Example:
    1. import geotrellis.vector._
      import geotrellis.slick._
      // create a web mercator projected point with the ExtendGeometry implicit class
      val projectedPoint = Point(1.0, 2.0).withSRID(3274)
  10. package spark

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  11. package util

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  12. package vector

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  13. package vectortile

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    This package is experimental. Expect API flux.

    This package is experimental. Expect API flux.

    Invented by Mapbox, VectorTiles are a combination of the ideas of finite-sized tiles and vector geometries. Mapbox maintains the official implementation spec for VectorTile codecs. The specification is free and open source.

    VectorTiles are advantageous over raster tiles in that:

    • They are typically smaller to store
    • They can be easily transformed (rotated, etc.) in real time
    • They allow for continuous (as opposed to step-wise) zoom in Slippy Maps.

    Raw VectorTile data is stored in the protobuf format. Any codec implementing the spec must decode and encode data according to this .proto schema.

    What is this package?

    geotrellis-vectortile is a high-performance implementation of Version 2.1 of the VectorTile spec. It features:

    • Decoding of Version 2 VectorTiles from Protobuf byte data into useful GeoTrellis types.
    • Lazy decoding of Geometries. Only parse what you need!

    Using this Package

    Modules

    Users of this library need only pay attention to geotrellis.vectortile. Any classes in the internal.* submodules are unique to the machinery of VectorTile {de,en}coding, and can be safely ignored.

    Types

    The central type is the VectorTile class. Its companion object can be used to construct VectorTiles from raw byte data:

    import geotrellis.spark.SpatialKey
    import geotrellis.spark.tiling.LayoutDefinition
    import geotrellis.vector.Extent
    import geotrellis.vectortile.VectorTile
    
    val bytes: Array[Byte] = ...  // from some `.mvt` file
    val key: SpatialKey = ...  // preknown
    val layout: LayoutDefinition = ...  // preknown
    val tileExtent: Extent = layout.mapTransform(key)
    
    /* Decode Protobuf bytes. */
    val tile: VectorTile = VectorTile.fromBytes(bytes, tileExtent)
    
    /* Encode a VectorTile back into bytes. */
    val encodedBytes: Array[Byte] = tile.toBytes

    The V* types form a small sum type and are used to represent usually untyped Feature-level metadata. This metadata is equivalent to a JSON Object, where String keys index values of any type. A Scala Map requires more rigidity (for the better), and so we use geotrellis.vectortile.Value to guarantee type safety.

    Implementation Assumptions

    This particular implementation of the VectorTile spec makes the following assumptions:

    • Geometries are implicitly encoded in some Coordinate Reference system. That is, there is no such thing as a "projectionless" VectorTile. When decoding a VectorTile, we must provide a GeoTrellis Extent that represents the Tile's area on a map. With this, the grid coordinates stored in the VectorTile's Geometry are shifted from their original [0,4096] range to actual world coordinates in the Extent's CRS.
    • The id field in VectorTile Features doesn't matter.
    • UNKNOWN geometries are safe to ignore.
    • If a VectorTile geometry list marked as POINT has only one pair of coordinates, it will be decoded as a GeoTrellis Point. If it has more than one pair, it will be decoded as a MultiPoint. Likewise for the LINESTRING and POLYGON types. A complaint has been made about the spec regarding this, and future versions may include a difference between single and multi geometries.
    Version

    2.1

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