modisfast (version 0.9.1)

mf_get_url: Build the URL(s) of the data to download

Description

Builds the OPeNDAP URL(s) of the spatiotemporal datacube to download, given a collection, variables, region and time range of interest.

Usage

mf_get_url(
  collection,
  variables = NULL,
  roi,
  time_range,
  output_format = "nc4",
  single_netcdf = TRUE,
  opt_param = NULL,
  credentials = NULL,
  verbose = TRUE
)

Value

a data.frame with one row for each dataset to download and 5 columns :

id_roi

Identifier of the ROI

time_start

Start Date/time for the dataset

collection

Name of the collection

name

Indicative name for the dataset

url

https OPeNDAP URL of the dataset

Arguments

collection

string. mandatory. Collection of interest (see details of mf_get_url).

variables

string vector. optional. Variables to retrieve for the collection of interest. If not specified (default) all available variables will be extracted (see details of mf_get_url).

roi

object of class sf. mandatory. Area of region of interest. Must be a Simple feature collection with geometry type POLYGON, composed of one or several rows (i.e. one or several ROIs), and with at least two columns: 'id' (an identifier for the roi) and 'geom' (the geometry).

time_range

date(s) / POSIXlt of interest . mandatory. Single date/datetime or time frame : vector with start and end dates/times (see details).

output_format

string. Output data format. optional. Available options are : "nc4" (default), "ascii", "json"

single_netcdf

boolean. optional. Get the URL either as a single file that encompasses the whole time frame (TRUE) or as multiple files (1 for each date) (FALSE). Default to TRUE. Currently enabled only for MODIS and VIIRS collections.

opt_param

list of optional arguments. optional. (see details).

credentials

vector string of length 2 with username and password. optional if the function mf_login was previously executed.

verbose

boolean. optional. Verbose (default TRUE)

Details

Argument collection : Collections available can be retrieved with the function mf_list_collections

Argument variables : For each collection, variables available can be retrieved with the function mf_list_variables

Argument time_range : Can be provided either as i) a single date (e.g. as.Date("2017-01-01")) or ii) a time frame provided as two bounding dates (starting and ending time) ( e.g. as.Date(c("2010-01-01","2010-01-30"))) or iii) a POSIXlt single time (e.g. as.POSIXlt("2010-01-01 18:00:00")) or iv) a POSIXlt time range (e.g. as.POSIXlt(c("2010-01-01 18:00:00","2010-01-02 09:00:00"))) for the half-hourly collection (GPM_3IMERGHH.06). If POSIXlt, times must be in UTC.

Argument single_netcdf : for MODIS and VIIRS products from LP DAAC: download the data as a single file encompassing the whole time frame (TRUE) or as multiple files : one for each date, which is the behavious for the other collections - GPM and SMAP) (FALSE) ?

Argument opt_param : list of parameters related to the queried OPeNDAP server and the roi. See mf_get_opt_param for additional details. This list can be retrieved outside the function with the function mf_get_opt_param. If not provided, it will be automatically calculated within the mf_get_url function. However, providing it fastens the processing time. It might be particularly useful to precompute it with mf_get_opt_param in case the function is used within a loop for a single ROI.

Argument credentials : Login to the OPeNDAP servers is required to use the function. Login can be done either within the function or outside with the function mf_login

Examples

if (FALSE) {

### First login to EOSDIS Earthdata with username and password.
# To create an account go to : https://urs.earthdata.nasa.gov/.
username <- "earthdata_un"
password <- "earthdata_pw"
log <- mf_login(credentials = c(username,password))

### Get the URLs to download the following datasets :
# MODIS Terra LST Daily (MOD11A1.061) (collection)
# Day + Night bands (LST_Day_1km,LST_Night_1km) (variables)
# over a 50km x 70km region of interest (roi)
# for the time frame 2017-01-01 to 2017-01-30 (30 days) (time_range)

roi <- sf::st_as_sf(data.frame(
id = "roi_test",
geom="POLYGON ((-5.82 9.54, -5.42 9.55, -5.41 8.84, -5.81 8.84, -5.82 9.54))"),
wkt="geom",crs = 4326)

time_range = as.Date(c("2017-01-01","2017-01-30"))

(urls_mod11a1 <- mf_get_url(
collection = "MOD11A1.061",
variables = c("LST_Day_1km","LST_Night_1km"),
roi = roi,
time_range = time_range
))

## Download the data :

res_dl <- mf_download_data(urls_mod11a1)

## Import as terra::SpatRast

modis_ts <- mf_import_data(dirname(res_dl$destfile[1]), collection = "MOD11A1.061")

## Plot the data

terra::plot(modis_ts)
}