How to download the MODIS data from R using MODISTools library

Question

I want to download MODIS product MOD13Q1 to use the Scientific Data Sets (SDS) layers of "250m_16_days_EVI", "250m_16_days_pixel_reliability". MODISTools library in R software provides the capability to download the MODIS data from LP DAAC data center.

I have read the MODISTools pdf guide which provides the basic understanding of how to use the library to subset the MOD13Q1 data layers by using the points location. The following subset function which I want to use:

library(`MODISTools`)
MODISSubsets(LoadDat = modis.subset, Products = "MOD13Q1",
Bands = c("250m_16_days_EVI", "250m_16_days_pixel_reliability"),
Size = c(1,1))

Here LoadDat = modis.subset is the data frame of latitude and longitude points in decimal format and according to Size = c(1,1) parameter that is used to extract the 1 Km left and 1 Km right from the focal point as extent. But I want to used the extent of whole study area like

lat <- c(23.6947, 37.0894)
long <- c(60.8786,  79.3074)
period <- data.frame(lat=lat,long=long, start.date=2013,end.date=2014,id=1)
MODISSubsets(LoadDat = period, Products = "MOD13Q1", Bands = "250m_16_days_EVI", "250m_16_days_pixel_reliability", Size = c(0,0), TimeSeriesLength = 1)

But here I am confused about using Size parameter that is used to extract the point values. How can I use it to extract all the available data in this extent? And second one is can I use this point information in ASCII file to display a raster in R software? I don't want to download the full tile which contains 250MB and in my case this will be 250GB data if I download all the available data starting from 2000 to 2015.

Answer 1

It seems the size data will be used to select the surrounding pixel and around the center pixel of your choice.

Size = c(1,1) will give you the output not only of the center pixel(or the point) but also 8 neighboring pixels.

So if you want to download the data only for the concerned point then give 'Size' value as c(0,0). See the Vignettes for more detail.

Now as for downloading the data, you can create a matrix of the coordinates of the raster. Then perhaps use it to download all the necessary data.