| Reading individual bits of MODIS BRDF quality files [message #68098] |
Fri, 18 September 2009 02:54 |
emitchard
Messages: 3
Registered: May 2008
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Junior Member |
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I am running IDL 7.0.6 on Windows vista (with ENVI 4.6). I am using
MODIS BRDF corrected 500 m data (MCD43A4). I have sucessfully written
a program to open the HDF files and produce the output vegetation
indices I'm interested in. However, I need to filter out cloud-
contaminated pixels, and am having problem reading the bit-packed
quality control file (MCD43A2).
I have written a program to extract the layer I'm interested in from
the HDF file and save it as a 32-bit unsigned integer. However, I
really need to extract the raw values of the first 12 bits of this
number (the values of the remaining fields do not matter to me). I
started writing a program to list all the numbers (from 0-4294967295)
that result from my required bit combination of these first 12 bits,
but that approach is not going to work as there are several million
'allowable' numbers.
Is there a function in IDL that can read individual bits, or any other
clever way to produce an array of 1s and 0s from a 32-bit integer?
Many thanks for your help,
Edward Mitchard
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