ST_Extend#

Table of Contents

  1. Setup BDT

  2. Generate Sample Data

    1. Line

    2. Multipath

  3. ST_Extend

    1. Line

    2. Multipath

Part 0: Setup BDT#

[ ]:

import bdt
bdt.auth("bdt.lic")
from bdt.processors import *
from bdt.functions import *
from pyspark.sql.functions import *
from pyspark.sql.types import StructType, StructField, StringType, IntegerType

BDT has been successfully authorized!

            Welcome to
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BDT python version: v3.3.0-v3.3.0
BDT jar version: v3.3.0-v3.3.0

Part 1: Generate Sample Data#

Part 1.1: Sample Data for Simple Line (2 points)#

drawing

[ ]:

line_wkt = "LINESTRING (0.0 0.0, 4.0 2.0)"

line_schema = StructType([StructField("LINE_ID", IntegerType()),
                          StructField("LINE_WKT", StringType())])

line_data = [(1, line_wkt),]

line_df = (
    spark
        .createDataFrame(data = line_data, schema = line_schema)
        .select(col("LINE_ID"), st_fromText("LINE_WKT").alias("SHAPE"))
)
line_df.show(truncate = True)

+-------+--------------------+
|LINE_ID|               SHAPE|
+-------+--------------------+
|      1|{[01 05 00 00 00 ...|
+-------+--------------------+

Part 1.2: Sample Data for Multipath (2 lines)#

drawing

[ ]:

multipath_wkt = "MULTILINESTRING ((0.0 0.0, 4.0 2.0), (3.0 4.0, 7.0 2.0))"

multipath_schema = StructType([StructField("MULTIPATH_ID", IntegerType()),
                          StructField("MULTIPATH_WKT", StringType())])

multipath_data = [(1, multipath_wkt),]

multipath_df = (
    spark
        .createDataFrame(data = multipath_data, schema = multipath_schema)
        .select(col("MULTIPATH_ID"), st_fromText("MULTIPATH_WKT").alias("SHAPE"))
)
multipath_df.show(truncate = True)

+------------+--------------------+
|MULTIPATH_ID|               SHAPE|
+------------+--------------------+
|           1|{[01 05 00 00 00 ...|
+------------+--------------------+

Part 2: ST_Extend#

  • ST_Extend supports lines with one or more segments as an argument, but not multipaths.

  • If ST_Extend needs to be used on multipaths, first use ST_Dump to extract each of the component lines into their own row in the DataFrame. Then, ST_Extend can be used on each of the component lines. Below, the two cases are illustrated (line and multipath).

Part 2.1: ST_Extend on Line#

  • Call ST_Extend on the simple line with two points.

  • ST_Extend takes the following arguments in order:

    1. The line SHAPE.

    2. The distance to extend in the origin direction.

    3. The distance to extend in the destination direction.

[ ]:

result_df = (
    line_df
        .select(st_extend("SHAPE", 2.0, 4.0).alias("SHAPE"))
        .select(st_asText("SHAPE").alias("WKT"))
)
result_df.show(truncate=False)

+-------------------------------------------------------------------------------------------------+
|WKT                                                                                              |
+-------------------------------------------------------------------------------------------------+
|MULTILINESTRING ((-1.7888543819998317 -0.8944271909999159, 7.577708763999663 3.7888543819998315))|
+-------------------------------------------------------------------------------------------------+

  • The red parts of the line are the parts added by ST_Extend.

drawing

Part 2.2: ST_Extend on Multipath#

  • ST_Extend does not support Multipaths. To use ST_Extend on a Multipath, first use ST_Dump to divide the multpath into its component lines.

[ ]:

line_df_2 = multipath_df.select(explode(st_dump("SHAPE")).alias("SHAPE"))

line_df_2_wkt = line_df_2.select(st_asText("SHAPE")).alias("WKT")

line_df_2_wkt.show(truncate=False)

+----------------------------+
|ST_AsText(SHAPE)            |
+----------------------------+
|MULTILINESTRING ((0 0, 4 2))|
|MULTILINESTRING ((3 4, 7 2))|
+----------------------------+

  • ST_Extend can be used now that each part (line) of the Multipath has been dumped into its own row.

  • Call ST_Extend on each of the two lines that composed the Multipath.

[ ]:

result_df = (
    line_df_2
        .select(st_extend("SHAPE", 2.0, 4.0).alias("SHAPE"))
        .select(st_asText("SHAPE").alias("WKT"))
)
result_df.show(truncate=False)

+-------------------------------------------------------------------------------------------------+
|WKT                                                                                              |
+-------------------------------------------------------------------------------------------------+
|MULTILINESTRING ((-1.7888543819998317 -0.8944271909999159, 7.577708763999663 3.7888543819998315))|
|MULTILINESTRING ((1.2111456180001683 4.894427190999916, 10.577708763999663 0.2111456180001683))  |
+-------------------------------------------------------------------------------------------------+

  • Each line of the Multpath is extended.

drawing