GetStatistics: Get statistical values

Description

Retrieves the simple statistics for the area of interest calculated based on satellite imagery without having to download images.

Usage

GetStatistics(
  aoi,
  bbox,
  time_range,
  collection,
  script,
  mosaicking_order = c("mostRecent", "leastRecent", "leastCC")[1],
  pixels,
  resolution,
  buffer = 0,
  percentiles = NULL,
  aggregation_period = 1L,
  aggregation_unit = c("day", "week", "month", "year")[1],
  lastIntervalBehavior = c("SKIP", "SHORTEN", "EXTEND")[1],
  as_data_frame = TRUE,
  client,
  token,
  url = getOption("CDSE.statistical_url")
)

Value

data.frame or list with statistical values.

Arguments

aoi

sf or sfc object, typically a (multi)polygon, describing the Area of Interest.

bbox

numeric vector of four elements describing the bounding box of interest. Specify with a coordinate pair on two (opposite) vertices of the bounding box rectangle. Coordinates need to be in longitude, latitude.

Only one of either aoi or bbox may be specified.

time_range

scalar or vector (Date or character that can be converted to date) defining the time interval.

collection

character indicating which collection to search. Must be one of the collections returned by GetCollections.

script

a length one character string containing the evaluation script or the name of the file containing the script.

mosaicking_order

character indicating the order in which tiles are overlapped from which the output result is mosaicked. Must be one of "mostRecent", "leastRecent", or "leastCC". Partial matching is used, that is, only enough initial letters of each string element are needed to guarantee unique recognition. Default: "mostRecent"

pixels

integer scalar or length-two vector indicating the request image width and height. Values must be integers between 1 and 2500.

resolution

numeric scalar or length-two vector indicating the spatial resolution of the request image in horizontal and vertical direction (in meters).

Only one of the arguments pixels or resolution must be set at the same time. If the argument pixels or resolution is scalar, the same value is used for horizontal and vertical direction (width and height).

buffer

numeric, width of the buffer to retrieve the image of enlarged area. Default: 0

percentiles

numeric vector indicating which percentile values should be computed. Default: NULL, don't compute any percentiles.

aggregation_period

the length of the aggregation period in aggregation_unit (days by default). Default: 1

aggregation_unit

character indicating the the unit of the aggregation period, must be one of "day", "week", "month", or "year". Partial matching is used, that is, only enough initial letters of each string element are needed to guarantee unique recognition (here just the first letter is enough). Default: "day"

lastIntervalBehavior

character indicating the behavior of the last interval if the given time_range isn't divisible by the provided aggregation_period. Must be one of:

SKIP: - skip the last interval (default behavior)

SHORTEN

- shortens the last interval so that it ends at the end of provided time_range

EXTEND

- extends the last interval over the end of the provided time range so that all intervals are of equal duration

Partial matching is used, that is, only enough initial letters of each string element are needed to guarantee unique recognition. Default: "SKIP"

as_data_frame

logical indicating if the result should be returned as data frame. Default: TRUE

client

OAuth client object to use for authentication.

token

OAuth token character string to use for authentication.

Exactly one of either client or token must be specified. It is recommended to use client.

url

character indicating the process endpoint. Default: Copernicus Data Space Ecosystem process endpoint

Details

The values are aggregated over the period (number of aggregation_units) given by the aggregation_period argument. The default values provide daily statistics. The statistics are returned only for the aggregation_units (days, weeks, months, years) when the data is available. This can be determined by the days of the satellite overpasses, but also by the calculations done in the evaluation script.

The scripts used for the Statistical API have some additional requirements: the evaluatePixel() function must, in addition to other output, always also return dataMask output. This output defines which pixels are excluded from calculations. For more information please visit the online documentation https://documentation.dataspace.copernicus.eu/APIs/SentinelHub/Statistical.html.

If a time_range is not divisible by an aggregation_period, the last ("not full") time interval will be dismissed by default (SKIP option). The user can instead set the lastIntervalBehavior to SHORTEN (shortens the last interval so that it ends at the end of the provided time range) or EXTEND (extends the last interval over the end of the provided time range so that all the intervals are of equal duration).

If percentiles requested are 25, 50, and 75, the columns are renamed 'q1', 'median', and 'q3'.

Examples

Run this code

if (FALSE) {
dsn <- system.file("extdata", "centralpark.geojson", package = "CDSE")
aoi <- sf::read_sf(dsn, as_tibble = FALSE)
script_file <- system.file("scripts", "NDVI_CLOUDS_STAT.js", package = "CDSE")
daily_stats <- GetStatistics(aoi = aoi, time_range = c("2023-07-01", "2023-07-31"),
  collection = "sentinel-2-l2a", script = script_file, mosaicking_order = "leastCC",
  resolution = 100, aggregation_period = 1, client = OAuthClient)
# specify week as 7 days
weekly_stats <- GetStatistics(aoi = aoi, time_range = c("2023-07-01", "2023-07-31"),
  collection = "sentinel-2-l2a", script = script_file,mosaicking_order = "leastCC",
  resolution = 100, aggregation_period = 7, client = OAuthClient)
# specify week as 1 week
weekly_stats_extended <- GetStatistics(aoi = aoi, time_range = c("2023-07-01", "2023-07-31"),
  collection = "sentinel-2-l2a", script = script_file, mosaicking_order = "leastCC",
  resolution = 100, aggregation_period = 1, aggregation_unit = "w",
  lastIntervalBehavior = "EXTEND", client = OAuthClient)
}