vsi_time_specific_orbits_wkt: Utilizing Virtual File Systems (vsi) and Well Known Text...

In IceSat2R: ICESat-2 Altimeter Data using R

Utilizing Virtual File Systems (vsi) and Well Known Text (WKT) to access the 'time specific orbits'

Description

Utilizing Virtual File Systems (vsi) and Well Known Text (WKT) to access the 'time specific orbits'

Usage

vsi_time_specific_orbits_wkt(
  date_from,
  date_to,
  RGTs,
  wkt_filter = NULL,
  download_zip = FALSE,
  verbose = FALSE
)

Arguments

date_from	a character string specifying the 'start' date in the format 'yyyy-MM-dd' (such as '2020-01-01')
date_to	a character string specifying the 'end' date in the format 'yyyy-MM-dd' (such as '2020-01-01')
RGTs	a character vector (consisting of one or more) Reference Ground Track (RGT). See the Examples section on how to come to these RGTs based on the "vsi_nominal_orbits_wkt()" function
wkt_filter	either NULL, or a Well Known Text (WKT) character string to allow a user to restrict to an area of interest rather than processing all data. It is possible that the WKT won't intersect with any of the available time specific orbits due to the sparsity of the coordinates (the output in that case will be an empty list)
download_zip	a boolean. If TRUE the .zip file will be first downloaded and then the .kml files will be returned, otherwise the 'gdalinfo' function will be used as input to the R 'system2()' function to read the .kml files without downloading the .zip file. The 'gdalinfo' command requires that the user has configured GDAL properly. Set the parameter 'download_zip' to TRUE if GDAL is not (properly) installed.
verbose	a boolean. If TRUE then information will be printed out in the console

Details

In case that this function does not return any results (empty list object) for a specified 'wkt_filter' parameter, then use a bigger Well Known Text (WKT) area. This is required because the 'time specific orbits' (points) are quite sparse.

Moreover, set the parameter 'download_zip' to TRUE if the 'gdalinfo' function returns internally an empty character string. In that case also a warning will be shown in the R session.

Value

a list of 'sf' objects where each sublist will represent a different RGT cycle

References

https://icesat-2.gsfc.nasa.gov/science/specs

https://gdal.org/user/virtual_file_systems.html

Examples

## Not run: 

require(IceSat2R)
require(magrittr)

#...........................................
# extracting nominal orbits only for the WKT
#...........................................

WKT = 'POLYGON ((-14.765 18.979, -11.25 18.979, -11.25 21.943, -14.765 21.943, -14.765 18.979))'

dat_rgt = vsi_nominal_orbits_wkt(orbit_area = 'western_hemisphere',
                                 track = 'GT3R',
                                 rgt_repeat = 8,
                                 wkt_filter = WKT,
                                 download_method = 'curl',
                                 download_zip = FALSE,
                                 verbose = TRUE)
str(dat_rgt)

out_rgt = dat_rgt[[1]]$RGT

#.........................................
# time specific RGTs (for a time interval)
# request using a single RGT cycle
#.........................................

date_start = '2020-01-01'
date_end = '2020-02-01'

orb_cyc_single = vsi_time_specific_orbits_wkt(date_from = date_start,
                                              date_to = date_end,
                                              RGTs = out_rgt,
                                              wkt_filter = WKT,
                                              verbose = TRUE)
str(orb_cyc_single)

#.........................................
# time specific RGTs (for a time interval)
# request using more than one RGT cycles
#.........................................

date_start = '2019-11-01'
date_end = '2020-01-01'

orb_cyc_multi = vsi_time_specific_orbits_wkt(date_from = date_start,
                                             date_to = date_end,
                                             RGTs = out_rgt,
                                             wkt_filter = WKT,
                                             verbose = TRUE)
str(orb_cyc_multi)
table(orb_cyc_multi$cycle)


#.......................................................
# visualization of the output cycles (including the WKT)
#.......................................................

orb_cyc_multi$cycle = as.factor(orb_cyc_multi$cycle)
mp_orb = mapview::mapview(orb_cyc_multi, legend = TRUE, zcol = 'cycle')

sf_aoi = sf::st_as_sfc(WKT, crs = 4326)
mp_aoi = mapview::mapview(sf_aoi, alpha.regions = 0.3, legend = F)

mp_orb + mp_aoi


## End(Not run)

IceSat2R documentation built on April 12, 2025, 1:44 a.m.