modiscloud (version 0.14)

get_bitgrid: Extract the value of a particular bit at each pixel

Description

Given an input grid (as a SpatialGridDataFrame object), extract a single desired bit value from all of the pixels

Usage

get_bitgrid(grd, bitnum)

Arguments

grd

A SpatialGridDataFrame, derived from e.g. readGDAL

bitnum

The bit you would like to extract

Value

grdr_vals_bits, a list of 0/1 values for the bit in question (numeric)

Details

Note: this means that, when interpreting the two 2-bit strings in the MODIS image, you would have to extract each bit separately.

References

Ackerman S, Frey R, Strabala K, Liu Y, Gumley L, Baum B and Menzel P (2010). "Discriminating clear-sky from cloud with MODIS algorithm theoretical basis document (MOD35)." MODIS Cloud Mask Team, Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin - Madison. .

GoldsmithMatzkeDawson2013

See Also

extract_bit

get_bitgrid_2bits

Examples

#######################################################
# Load a TIF
#######################################################
# Code excluded from CRAN check because it depends on modiscdata
## Not run: 
# library(devtools)
# # The modiscdata (MODIS c=cloud data=data) package is too big for CRAN (60 MB); so it is available on github:
# # https://github.com/nmatzke/modiscdata
# # If we can't get install_github() to work, try install_url():
# # install_github(repo="modiscdata", username="nnmatzke")
# install_url(url="https://github.com/nmatzke/modiscdata/archive/master.zip")
# library(modiscdata)
# tifsdir = system.file("extdata/2002tif/", package="modiscdata")
# tiffns = list.files(tifsdir, pattern=".tif", full.names=TRUE)
# tiffns
# 
# library(rgdal)	# for readGDAL
# 
# # numpixels in subset
# xdim = 538
# ydim = 538
# 
# 
# # Read the grid and the grid metadata
# coarsen_amount = 1
# xdim_new = xdim / floor(coarsen_amount)
# ydim_new = ydim / floor(coarsen_amount)
# 
# fn = tiffns[1]
# grd = readGDAL(fn, output.dim=c(ydim_new, xdim_new))
# 
# grdproj = CRS(proj4string(grd))
# grdproj
# grdbbox = attr(grd, "bbox")
# grdbbox
# 
# #######################################################
# # Extract a particular bit for all the pixels in the grid
# #######################################################
# bitnum = 2
# grdr_vals_bits = get_bitgrid(grd, bitnum)
# length(grdr_vals_bits)
# grdr_vals_bits[1:50]
# ## End(Not run)