ST_PointN

ST_PointN takes a geometry column and an integer and returns a point column. The output column represents the n^th point in the input geometry, where 0 is the first point. If the n^th point does not exist the function returns null. This function always returns null for multipart linestrings and multipart polygons.

Function	Syntax
Python	`point_n(geometry, n)`
SQL	`ST_PointN(geometry, n)`

For more details, go to the GeoAnalytics Engine API reference for point_n.

This function implements the OpenGIS Simple Features Implementation Specification for SQL 1.2.1.

Examples

Python

SQL

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from geoanalytics.sql import functions as ST

data = [
    ("POINT (10 30)",),
    ("MULTIPOINT (0 0, 5 5, 0 5)", ),
    ("LINESTRING (15 15, 10 15, 12 2)", ),
    ("POLYGON ((20 30, 18 28, 22 35, 40 20))", ),
    ("MULTILINESTRING ((0 0, 10 10), (10 10, 20 20))", )
]

df = spark.createDataFrame(data, ["wkt"])\
          .select(ST.geom_from_text("wkt").alias("geometry"))

df.select(ST.point_n("geometry", 2).alias("point_n")).show()

Result
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+---------------+
|        point_n|
+---------------+
|           NULL|
|  {"x":0,"y":5}|
| {"x":12,"y":2}|
|{"x":22,"y":35}|
|           NULL|
+---------------+

Version table

Release	Notes
1.0.0	Function introduced

ST_PointN

Examples

Version table

Related topics