Function to create thumbnail images for Sentinel-2 products. BOA and TOA multiband images are rendered as false colour JPEG images; SCL maps are rendered as 8-bit PNG; other singleband images (like spectral indices) are rendered as JPEG images with a standard colour palette. Output images are georeferenced.

s2_thumbnails(
infiles,
prod_type = NA,
rgb_type = "SwirNirR",
dim = 1024,
scaleRange = NA,
outdir = NA,
tmpdir = NA,
rmtmp = TRUE,
proc_mode = "raster",
overwrite = FALSE
)

## Arguments

infiles A vector of input filenames. Input files are paths of products already converted from SAFE format to a format managed by GDAL (use s2_translate to do it); their names must be in the sen2r naming convention (safe_shortname). (optional) Output product (see safe_shortname for the list of accepted products). If not provided, it is retrieved from the file name. (optional) For BOA and TOA products, this value determine the type of false colours to be used for the thumbnails: "SwirNirR" (default) for SWIR-NIR-Red; "NirRG" for NIR-Red-Green; "RGB" for true colours; Integer value, with the maximum greater dimension in pixels (width or height) of the output images (default: 1024 px). If this is lower than the corresponding dimension of the maps, maps are rescaled before producing the thumbnails; otherwise the original dimensions are maintained. To keep the original size in any case, set dim = Inf. (optional) Range of valid values. If not specified (default), it is automatically retrieved from the product type. Default ranges for BOA and TOA products are 0 to 8000 (rgb_type = "SwirNirR"), 0 to 7500 ("NirRG") and 0 to 2500 ("RGB"). For spectral indices, default range is -1 to 1 for Float products, -10000 to 10000 for Int and 0 to 200 for Byte; for "Zscore" products, default range is -3 to 3 for Float and -3000 to 3000 for Int. It can be useful i.e. to stretch BOA "dark" products. (optional) Full name of the existing output directory where the files should be created. Default is a subdirectory (named "thumbnails") of the parent directory of each input file. (optional) Path where intermediate files (VRT) will be created. Default is a temporary directory. If tmpdir is a non-empty folder, a random subdirectory will be used. (optional) Logical: should temporary files be removed? (Default: TRUE) (optional) Character: if "gdal_calc", gdal_calc routines are used to compute indices; if "raster" or "stars", R functions are instead used (using respectively raster or stars routines). Note: default value ("raster") is the only fully supported mode. "gdal_calc" can be used only if a runtime GDAL environment can be properly configured (no assistance is provided in case of GDAL-related problems). "raster" mode is experimental. See s2_calcindices() for further details. (optional) Logical value: should existing thumbnails be overwritten? (default: TRUE)

## Value

A vector with the names of the created images.

License: GPL 3.0

## References

L. Ranghetti, M. Boschetti, F. Nutini, L. Busetto (2020). "sen2r": An R toolbox for automatically downloading and preprocessing Sentinel-2 satellite data. Computers & Geosciences, 139, 104473. doi: 10.1016/j.cageo.2020.104473 , URL: https://sen2r.ranghetti.info/.

## Author

Luigi Ranghetti, phD (2019) luigi@ranghetti.info