ct_solartime: Transform time to solar time anchored to sunrise and sunset

In ct: Camera Trap Data Management and Multi-Method Ecological Analysis

Transform time to solar time anchored to sunrise and sunset

Description

This function converts local time to solar time based on the sunrise and sunset times for a given location. Solar time is a timekeeping system where the day is defined by the position of the sun in the sky, with sunrise marking the start of the day and sunset marking the end.

Usage

ct_solartime(
  data = NULL,
  date,
  longitude,
  latitude,
  crs = NULL,
  format,
  time_zone,
  ...
)

Arguments

data	A data frame containing the date, longitude, and latitude columns. If NULL, the function will use the date, longitude, and latitude parameters directly. Default is NULL.
date	A vector of date-time values or a column name in data representing the date-time values to be converted to solar time. This can be a character vector or a POSIXlt object.
longitude	A numeric vector or a column name in data representing the longitude of the location(s). Longitude should be in decimal degrees.
latitude	A numeric vector or a column name in data representing the latitude of the location(s). Latitude should be in decimal degrees.
crs	A coordinate reference system (CRS) string or object specifying the current CRS of the input coordinates. If provided, the function will transform the coordinates to longitude and latitude (WGS84). This is useful when the input coordinates are in a projected system (e.g., UTM). Default is NULL.
format	character string giving a date-time format as used by strptime().
time_zone	A numeric vector representing the time zone offset(s) from UTC (in hours). If data is provided, this should match the number of unique locations in the data.
...	Additional arguments passed to as.POSIXlt for date parsing.

Details

The function calculates solar time by first determining the sunrise and sunset times for the given location(s) and date(s). It then uses these times to anchor the solar time calculation. The solar time is computed by transforming the local clock time based on the position of the sun in the sky.

If data is provided, the function will process each unique location in the data and return a tibble with the solar time for each date-time value. If data is NULL, the function will process the date, longitude, and latitude parameters directly.

Value

A tibble with the following columns:

• input: The original date-time values.

• clock: The local clock time.

• solar: The calculated solar time.

If data is provided, the tibble will also include the longitude and latitude columns.

References

Rowcliffe, M. (2023). activity: Animal Activity Statistics. R package version 1.3.4. https://CRAN.R-project.org/package=activity

Examples

library(dplyr)
data(penessoulou)

cam_data <- penessoulou %>%
  dplyr::filter(project == "Last") %>%
 dplyr::filter(species == "Erythrocebus patas") %>%
 # Select independent events based on a given threshold
 ct::ct_independence(species_column = species,
                          datetime = datetimes, threshold = 60*5, # 5 minutes
                          format = "%Y-%m-%d %H:%M:%S"
                          ) %>%
 # Transform Time to Solar Time
 ct_solartime(data = ., date = datetime, longitude = longitude, latitude = latitude,
               crs = "EPSG:32631", time_zone = 1)

ct documentation built on Oct. 22, 2026, 1:07 a.m.