get_bitgrid: Extract the value of a particular bit at each pixel
In modiscloud: R tools for processing Level 2 Cloud Mask products from MODIS

Description Usage Arguments Details Value Author(s) References See Also Examples

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

1	get_bitgrid(grd, bitnum)

`grd`	A SpatialGridDataFrame, derived from e.g. readGDAL
`bitnum`	The bit you would like to extract

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

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

Nicholas J. Matzke matzke@berkeley.edu

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. <URL: http://modis-atmos.gsfc.nasa.gov/_docs/MOD35_ATBD_Collection6.pdf>.

GoldsmithMatzkeDawson2013

extract_bit

get_bitgrid_2bits

#######################################################
# 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)