stk_screen_twl: Twilight screening routine

In skytrackr: A Sky Illuminance Location Tracker

Twilight screening routine

Description

Removes poor quality data based on twilight heuristics. Allows for quick screening of data containing "false" twilight values.

Usage

stk_screen_twl(df, threshold = 1.5, dips = 3, step = 100, filter = TRUE)

Arguments

df	A skytrackr data frame.
threshold	A twilight threshold (default = 1.5).
dips	The allowed number of interruptions during a daylight profile below the twilight threshold before flagging as a poor quality "suspect" day.
step	A threshold of the allowed step change in illuminance values between the twilight value and the preceding one. Large jumps and the lack of a smooth transition suggest a false twilight (bird leaving a dark nest site long after or long before dawn or dusk).
filter	Logical if to return data pre-filtered, removing all poor quality days or false twilight ones (default = TRUE)

Value

A skytrackr data frame with poor twilight quality days removed and dusk and dawn timings marked (data is returned as a long format, not a wide format).

Examples

# set demo values artificially low as a demonstration
library(dplyr)
df <- cc876 |>
  mutate(
  value = ifelse(
    date_time > "2021-08-15 05:00:00" & date_time < "2021-08-15 12:00:00",
    0.1,
    value)
  )

# screen values and remove them (filter = TRUE)
df <- df |> stk_screen_twl(filter = TRUE)

skytrackr documentation built on Nov. 5, 2025, 6:47 p.m.