GetSubset: Subset download using MODIS web service method.

Description

Internal function that uses the MODIS SOAP Web Service (see references) getsubset method to download a requested time-series subset of a MODIS product for a given area surrounding many locations. This function is used by the MODISSubsets function, which is the main subset download tool for the user.

Usage

GetSubset(Lat, Long, Product, Band, StartDate, EndDate, KmAboveBelow, KmLeftRight)

Arguments

Lat

Numeric; a decimal degrees latitude in WGS-1984 coordinate system.

Long

Numeric; a decimal degrees longitude in WGS-1984 coordinate system.

Product

A character string; a product code to request the subset from. The MODIS product table shows all available products and their respective product titles (see references).

Band

A character string; a code or vector of codes to retrieve the desired data band(s) within the specified product to be requested. To get a list of the available bands in a product of interest use GetBands().

StartDate

Character; in MODIS date format, listing the date to begin the time-series for each corresponding location.

EndDate

Character; in MODIS date format, listing the date to end the time-series for each corresponding location.

KmAboveBelow

An integer; the distance, in kilometres, from the centre of the tile of pixels to the top and bottom of the tile. So, if KmAboveBelow=1, the total distance from top to bottom of the tile will be 2km.

KmLeftRight

An integer; the distance, in kilometres, from the centre of the tile of pixels to the left and right sides of the tile. So, if KmLeftRight=1, the total distance from side to side of the tile will be 2km.

Value

A data frame containing: xll=The x coordinate, in the MODIS coordinate system, of the lower left corner of the pixel in which the location data falls. yll=The y coordinate, in the MODIS coordinate system, of the lower left corner of the pixel in which the location data falls. pixelsize=The actual calculated width of the pixels of interest, in metres. nrow=Corresponds to KmAboveBelow argument. ncol=Corresponds to KmLeftRight argument. band=Corresponds to band argument. scale=The number by which raw downloaded data values can be scaled by. Specific to each band. lat=Corresponds to the Lat argument. long=Corresponds to the Long argument. subset=The downloaded data, as a vector of character strings, with length number of time-steps requested, that include data attached to metadata. This data frame is then passed to MODISSubsets.

References

https://daacmodis.ornl.gov/cgi-bin/MODIS/GLBVIZ_1_Glb/modis_subset_order_global_col5.pl

Examples

Run this code

## Not run: ------------------------------------
# # dontrun() used because running the example requires internet access,
# # and takes over a minute to run.
# data(SubsetExample)
# GetSubset(Lat=SubsetExample[ ,1], Long=SubsetExample[ ,2], Product="MOD13Q1",
#     Band="250m_16_days_EVI", StartDate="A2001001", EndDate="A2001025",
#     KmAboveBelow=0, KmLeftRight=0)
## ---------------------------------------------