rstac

R Client Library for SpatioTemporal Asset Catalog (rstac)

STAC is a specification of files and web services used to describe geospatial information assets. The specification can be consulted in https://stacspec.org/.

R client library for STAC (rstac) was designed to fully support STAC API v1.0.0. It also supports earlier versions (>= v0.8.0).

Installation

# install via CRAN 
install.packages("rstac")

Development version

To install the development version of rstac, run the following commands

# load necessary libraries
library(devtools)
install_github("brazil-data-cube/rstac")

Importing rstac package:

library(rstac)
library(magrittr) # for pipe (%>%) in examples

Usage

rstac implements the following STAC endpoints:

These functions can be used to retrieve information from a STAC API service. The code bellow creates a stac object and list the available collections of the STAC API of the Brazil Data Cube project of the Brazilian National Space Research Institute INPE.

s_obj <- stac("https://brazildatacube.dpi.inpe.br/stac/")

get_request(s_obj)
#> ###STACCatalog
#> - id: bdc
#> - description: Brazil Data Cube Catalog
#> - field(s): description, id, stac_version, links

The variable s_obj stores information to connect to the Brazil Data Cube STAC web service. The get_request method makes a HTTP GET connection to it and retrieves a STAC Catalog document from the server. Each links entry is an available collection that can be accessed via STAC API.

In the code bellow, we get some STAC items of CB4_64_16D_STK-1 collection that intersects the bounding box passed to the bbox parameter. To do this, we call the stac_search function that implements the STAC /search endpoint. The returned document is a STAC Item Collection (a geojson containing a feature collection).

it_obj <- s_obj %>% 
    stac_search(collections = "CB4_64_16D_STK-1",
                bbox = c(-47.02148, -12.98314, -42.53906, -17.35063)) %>%
    get_request()

it_obj
#> ###STACItemCollection
#> - matched feature(s): 264
#> - features (10 item(s) / 254 not fetched):
#>   - CB4_64_16D_STK_v001_022024_2021-09-14_2021-09-29
#>   - CB4_64_16D_STK_v001_022025_2021-09-14_2021-09-29
#>   - CB4_64_16D_STK_v001_022024_2021-08-29_2021-09-13
#>   - CB4_64_16D_STK_v001_022025_2021-08-29_2021-09-13
#>   - CB4_64_16D_STK_v001_022024_2021-08-13_2021-08-28
#>   - CB4_64_16D_STK_v001_022025_2021-08-13_2021-08-28
#>   - CB4_64_16D_STK_v001_022024_2021-07-28_2021-08-12
#>   - CB4_64_16D_STK_v001_022025_2021-07-28_2021-08-12
#>   - CB4_64_16D_STK_v001_022024_2021-07-12_2021-07-27
#>   - CB4_64_16D_STK_v001_022025_2021-07-12_2021-07-27
#> - assets: 
#> EVI, NDVI, CMASK, BAND13, BAND14, BAND15, BAND16, CLEAROB, TOTALOB, thumbnail, PROVENANCE
#> - other field(s): type, links, context, features

The rstac uses the httr package to manage HTTP requests, allowing the use of tokens from the authorization protocols OAuth 1.0 or 2.0 as well as other configuration options. In the code below, we present an example of how to pass a parameter token on a HTTP request.

it_obj <- s_obj %>% 
    stac_search(collections = "CB4_64_16D_STK-1",
                bbox = c(-47.02148, -12.98314, -42.53906, -17.35063)) %>%
    get_request(add_headers("x-api-key" = "MY-TOKEN"))

In addition to the functions mentioned above, the rstac package provides some extra functions for handling items and to bulk download the assets.

Items functions

rstac provides some functions to facilitates the interaction with STAC data. In the example bellow, we get how many items matched the search criteria:

# it_obj variable from the last code example
it_obj %>% items_matched()
#> [1] 264

However, if we count how many items there are in it_obj variable, we get 10, meaning that more items could be fetched from the STAC service:

it_obj %>% items_length()
#> [1] 10

# fetch all items from server 
# (but don't stored them back in it_obj)
it_obj %>% items_fetch(progress = FALSE) %>%
    items_length()
#> [1] 264

Download assets

All we’ve got in previous example was metadata to STAC Items, including links to geospatial data called assets. To download all assets in a STAC Item Collection we can use assets_download() function, that returns an update STAC Item Collection referring to the downloaded assets. The code bellow downloads the thumbnail assets (.png files) of 10 items stored in it_obj variable.

download_items <- it_obj %>% 
    assets_download(assets_name = "thumbnail")

How to contribute?

The rstac package was implemented based on an extensible architecture, so feel free to contribute by implementing new STAC API extensions/fragments based on the STAC API specifications.

1. Make a project fork.
2. Create a file inside the R/ directory called ext_{extension_name}.R.
3. In the code, you need to specify a subclass name (e.g.ext_subclass) for your extension in RSTACQuery function constructor, and implement the S3 generics methods: get_endpoint, before_request, and after_response. Using these S3 generics methods you can define how parameters must be submitted to the HTTP request and the types of the returned documents responses. See the implemented ext_query API extension as an example.
   
4. Make a Pull Request on the branch dev.

Getting help

You can get a full explanation about each STAC (v1.0.0) endpoint at STAC API spec. A detailed documentation with examples on how to use each endpoint and other functions available in the rstac package can be obtained by typing ?rstac in R console.

Citation

To cite rstac in publications use:

R. Simoes, F. C. de Souza, M. Zaglia, G. R. de Queiroz, R. D. C. dos Santos and K. R. Ferreira, “Rstac: An R Package to Access Spatiotemporal Asset Catalog Satellite Imagery,” 2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS, 2021, pp. 7674-7677, doi: 10.1109/IGARSS47720.2021.9553518.