TheiaR package

The TheiaR package intends to provide a clean interface to download and manage data issued by Theia through its API (Application Programming Interface).

The basic functionalities are (for now):

NOTE: ongoing development, more functionalities shall be added in the future

Step-by-step guide

First, load the package.

library(theiaR)

To search and download data from Theia, you will need to register to their website.

NOTE: In order to use Landsat or SpotWorldHeritage products, you'll need to make a first manual download to agree to the license and validate your account.

Create a collection of tiles

The first step is to create a collection of tile(s). This can be done either from a query or from a cart file.

Create a collection from a query

A query is simply a named list of search terms. For example:

myquery <- list(collection  = "SENTINEL2",
                town        = "Grenoble",
                start.date  = "2018-07-01",
                end.date    = "2018-07-06")

will create a query to Theia database, looking for tiles from Sentinel2 satellite around Grenoble, between 2018-07-01 and 2018-07-31.

It accepts the following terms. Terms with a * are mandatory.

To specify the location of the tiles, several alternatives are available. You can specify the town around which you want your data with:

You can specify directly the tile ID if you know it:

You can specify a point by giving its x/y coordinates:

Or you can specify a rectangle by giving its min/max coordinates:

Finally, you can filter results by giving the date range and the maximum cloud cover:

You can then create your collection with:

mycollection <- TheiaCollection$new(query = myquery, dir.path = ".")

where dir.path is the path you want your tiles to be downloaded. If tiles are already present in dir.path, they will be checked by computing a checksum and comparing it to the hash provided by Theia (only available for Sentinel2 data, no hash is provided for other collections, and files are then assumed to be correct). This ensures that the files have been correctly downloaded.

print(mycollection)
#> An collection of tiles from Theia
#> 
#> Number of tiles: 11 
#> Directory path : '.'
#> 
#> Obtained from query

Create a collection from a cart file

Alternatively, you can download a cart from Theia. To create a cart, login to Theia website, make a search for tiles, and add wanted tiles to your cart. Then, download your cart and save the resulting .meta4 file to your disk.

You can then create your collection using this file:

cart.path <- system.file("extdata", "cart.meta4", package = "theiaR")

mycollection <- TheiaCollection$new(cart.path = cart.path,
                                    dir.path  = ".")

print(mycollection)
#> An collection of tiles from Theia
#> 
#> Number of tiles: 2 
#> Directory path : '.'
#> 
#> Obtained from cart file

As above, it will check the hash of files if they are already present in dir.path.

Download your tiles

The next step is to download your collection. You can get the status of your collection by running:

mycollection$status
#>                                             tile exists checked correct
#> SENTINEL2B_20190128-104831-308_L2A_T31TGK_D       FALSE   FALSE   FALSE
#> SENTINEL2A_20190113-104826-809_L2A_T31TGK_D       FALSE   FALSE   FALSE

To download all tiles in a collection, simply run:

mycollection$download(auth = myauth)

where myauth is the path to file storing your Theia credentials. If it does not exist yet, you will be securely prompted for your login and password, and the file will be created.

This will check if files are present, check their hashes, and download them if needed (if files do not exist or checksums are wrong). To overwrite existing files, run:

mycollection$download(auth = myauth, overwrite = TRUE)

Read your tiles

Once you have downloaded every tile (as an archive), you can read images contained in the archive without extracting it. This allows to save a lot of disk space.

First, get a list of bands available in the tiles by running:

mycollection$get_bands()

Then you can read bands with:

images.list <- mycollection$read(bands = c("B2", "B3")

where bands is a vector with bands names.

It will return a list of RasterLayer objects, that you can manipulate with functions from the raster package.

Extract tiles

If you want to extract full archives, you can run:

file.path <- mycollection$extract()

which will extract tiles into the same directory as the archives.

Acknowledgment

Thanks to Olivier Hagolle for his work on theia_download.py (github), which has inspired this package.