TheiaR: search, download and manage data from Theia

The TheiaR package provides an efficient and clean interface to search, download and manage products from Theia website.

Overview

The basic functionalities are:

• Search available tiles through Theia API
• Download tiles resulting from a search
• Download tiles contained in a cart (.meta4 file) obtained from Theia website.
• Read band into RasterStack objects (with the raster library)
• Read band into gdalcubes objects (with the gdalcubes library)
• Extract archives (not recommended)

NOTE: 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.

Installation

You can install the latest stable version from Github with:

devtools::install_github('norival/theiaR')

# or, to install the development version
devtools::install_github('norival/theiaR', 'devel')

Or, you can install it from CRAN:

isntall.packages('theiaR')

Complete example

A workflow to search and download tiles would be something like:

library(theiaR)

# create a list containing the query
myquery <- list(collection = "SENTINEL2",
                town       = "Grenoble",
                start.date = "2018-07-01",
                end.date   = "2018-07-06")

# create a collection from the query
mycollection <- TheiaCollection$new(query = myquery, dir.path = ".", check = TRUE)

# check available tiles fro the query
mycollection$status

# download the tiles into 'dir.path'
mycollection$download(auth = "path/to/auth/file.txt")

Step-by-step guide

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 (downloaded from Theia’s website).

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.

See the vignette for all the available options.

You can then create your collection with:

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

where dir.path is the path you want your tiles to be further downloaded (This only queries Theia’s catalog for available tiles, nothing is 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. Set check = FALSE to skip file’s check.

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:

mycollection <- TheiaCollection$new(cart.path = "path/to/cart/file.meta4",
                                    dir.path  = ".",
                                    check     = TRUE)

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

Getting information on your collection

You can access the tiles from your collection using:

mycollection$tiles

which returns a list of tiles. You can also see the status of your collection with:

mycollection$status

Download your tiles

The next step is to download your collection. To download all tiles in a collection, simply run:

mycollection$download(auth = "path/to/auth/file.txt")

where path/to/auth/file.txt is the path to a file storing your Theia credentials. It is a simple text file with the Theia’s account email on the first line and the account’s password on the second line:

user@example.com
MyTheiaPassword

If it does not exist yet, you will be securely prompted for your login and password, and the file will be created.

The download() method 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 = "path/to/auth/file.txt", overwrite = TRUE)

Read bands from zip files

You can then read bands directly from the zip archives (by using the vsizip interface provided by GDAL). Use:

mytile$bands

to get a list of available bands. Then:

mybands <- mytile$read(bands = c("B5", "B6"))

to load the bands into memory (returns a RasterStack object). It performs the necessary corrections on the values.

You can also read bands from a collection by running:

mybands <- mycollection$read(bands = c("B5", "B6"))

which returns a list of RasterStack objects.

NOTE: Be careful when loading several tiles as it needs a lot of memory (~900MB/tile)

Create a gdalcubes collection

Alternatively, you can use the great gdalcubes package to create a three dimensional representation of the tiles. Simply run:

library(gdalcubes)

gdalcubes <- mycollection$as_gdalcube("path/to/gdalcubes.sqlite")

where path/to/gdalcubes.sqlite is the path to store the gdalcubes object data.

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.

This is not recommended, as this will take a large amount of disk space

Acknowledgments

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