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

In modisfast: Fast and Efficient Access to MODIS Earth Observation Data

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
)

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

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

Examples

## Not run: 

### 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)

## End(Not run)

modisfast documentation built on Sept. 11, 2024, 8:15 p.m.