TRK_Before takes a track column and an offset and returns a track. The result is the subset of the input track that is between the track start and the offset distance or offset duration.
An offset column can be created with ST_CreateDistance or
ST_CreateDuration. You can also define an offset with a tuple
containing a number and a unit string (e.g., (10, "kilometers") or (5, "minutes")).
For example, if you use a distance offset of 2 miles, the result track will be the subset of the input track that is no further than 2 miles along the input track's length from its start. Similarly, if you use a duration offset of 10 minutes, the result track will be the subset of the input track that is no longer than 10 minutes from its start time.
Tracks are linestrings that represent the change in an entity's location over time. Each vertex in the linestring has a timestamp (stored as the M-value) and the vertices are ordered sequentially.
For more information on using tracks in GeoAnalytics Engine, see the core concept topic on tracks.
| Function | Syntax |
|---|---|
| Python | before(track, offset) |
| SQL | TRK |
For more details, go to the GeoAnalytics Engine API reference for before.
Examples
from geoanalytics.sql import functions as ST
from geoanalytics.tracks import functions as TRK
data = [
("LINESTRING M (-117.27 34.05 1633455010, -117.22 33.91 1633456062, -116.96 33.64 1633457132)",),
("LINESTRING M (-116.89 33.96 1633575895, -116.71 34.01 1633576982, -116.66 34.08 1633577061)",),
("LINESTRING M (-116.24 33.88 1633575234, -116.33 34.02 1633576336)",)
]
df = spark.createDataFrame(data, ["wkt"]).withColumn("track", ST.line_from_text("wkt", srid=4326)) \
.withColumn("10_minutes", TRK.query("track", (10, "minutes"))) \
.withColumn("start_point", ST.start_point("track")) \
.withColumn("end_point", ST.end_point("track"))
result = df.withColumn("before", TRK.before("track", (10, "minutes")))
ax = result.st.plot("track", edgecolor="lightgrey", linewidths=10, zorder=0, figsize=(15, 8))
result.st.plot("start_point", ax=ax, s=75, facecolor="green", zorder=2)
result.st.plot("end_point", ax=ax, s=75, facecolor="red", zorder=2)
result.st.plot("10_minutes", ax=ax, s=75, facecolor="black", marker="x", zorder=2)
result.st.plot("before", ax=ax, edgecolor="greenyellow", linewidths=3, zorder=1)
ax.legend(['Input track','Input track start','Input track end','10 minutes along input track','Result track'],
loc='lower right', fontsize='x-large')
Version table
| Release | Notes |
|---|---|
1.4.0 | Function introduced |