DataFrame/SQL
Quick start¶
The detailed explanation is here: Visualize Spatial DataFrame/RDD.
- Add Sedona-core, Sedona-SQL, Sedona-Viz into your project pom.xml or build.sbt
- Declare your Spark Session
sparkSession = SparkSession.builder().
config("spark.serializer","org.apache.spark.serializer.KryoSerializer").
config("spark.kryo.registrator", "org.apache.sedona.viz.core.Serde.SedonaVizKryoRegistrator").
master("local[*]").appName("mySedonaVizDemo").getOrCreate()
- Add the following lines after your SparkSession declaration:
SedonaSQLRegistrator.registerAll(sparkSession)
SedonaVizRegistrator.registerAll(sparkSession)
Regular functions¶
ST_Colorize¶
Introduction: Given the weight of a pixel, return the corresponding color. The weight can be the spatial aggregation of spatial objects or spatial observations such as temperature and humidity.
Note
The color is encoded to an Integer type value in DataFrame. When you print it, it will show some nonsense values. You can just treat them as colors in GeoSparkViz.
Format:
ST_Colorize (weight: Double, maxWeight: Double, mandatory color: String (Optional))
Since: v1.0.0
Produce various colors - heat map¶
This function will normalize the weight according to the max weight among all pixels. Different pixel obtains different color.
SQL Example
SELECT pixels.px, ST_Colorize(pixels.weight, 999) AS color
FROM pixels
Produce uniform colors - scatter plot¶
If a mandatory color name is put as the third input argument, this function will directly output this color, without considering the weights. In this case, every pixel will possess the same color.
SQL Example
SELECT pixels.px, ST_Colorize(pixels.weight, 999, 'red') AS color
FROM pixels
Here are some example color names can be entered:
"firebrick"
"#aa38e0"
"0x40A8CC"
"rgba(112,36,228,0.9)"
Please refer to AWT Colors for a list of pre-defined colors.
ST_EncodeImage¶
Introduction: Return the base64 string representation of a Java PNG BufferedImage. This is specific for the server-client environment. For example, transfer the base64 string from GeoSparkViz to Apache Zeppelin.
Format: ST_EncodeImage (A: Image)
Since: v1.0.0
SQL Example
SELECT ST_EncodeImage(images.img)
FROM images
ST_Pixelize¶
Introduction: Convert a geometry to an array of pixels given a resolution
You should use it together with Lateral View and Explode
Format:
ST_Pixelize (A: Geometry, ResolutionX: Integer, ResolutionY: Integer, Boundary: Geometry)
Since: v1.0.0
SQL Example
SELECT ST_Pixelize(shape, 256, 256, (ST_Envelope_Aggr(shape) FROM pointtable))
FROM polygondf
ST_TileName¶
Introduction: Return the map tile name for a given zoom level. Please refer to OpenStreetMap ZoomLevel and OpenStreetMap tile name.
Note
Tile name is formatted as a "Z-X-Y" string. Z is zoom level. X is tile coordinate on X axis. Y is tile coordinate on Y axis.
Format: ST_TileName (A: Pixel, ZoomLevel: Integer)
Since: v1.0.0
SQL Example
SELECT ST_TileName(pixels.px, 3)
FROM pixels
Aggregate functions¶
ST_Render¶
Introduction: Given a group of pixels and their colors, return a single Java PNG BufferedImage. The 3rd parameter is optional and it is the zoom level. You should use zoom level when you want to render tiles, instead of a single image.
Format: ST_Render (A: Pixel, B: Color, C: Integer - optional zoom level)
Since: v1.0.0
SQL Example
SELECT tilename, ST_Render(pixels.px, pixels.color) AS tileimg
FROM pixels
GROUP BY tilename