Okay - unfortunately i am now totally confused. I have tried to read up on
binary data (to little or no avail!!!). My understanding is the MODIS
suf_refl_qc data that i have import is a unsigned 16 bit integer number. I
would like to select out pixels using this raster to create a cloud mask
based on some of the bit codes.
for example identify " band 1 quality = missing input" would have the
following
* * * * 1 0 1 1 * * * * * * * * * - where * represents placeholder
If i try and follow Glynn's logic he is saying divide the number by 16 and
then take the modulus 16 and then equate it to "11" to get the subset.
I am unsure how I choose the "11" and how do i change the syntax to pull
out the different masks i may be interested in.
0 0 * * * * * * * * * * * * * * ideal quality all bands
0 1 * * * * * * * * * * * * * * less than ideal quality
* * 0 0 * * * * * * * * * * * * clear
* * 0 1 * * * * * * * * * * * * cloudy
* * 1 0 * * * * * * * * * * * * mixed
* * * * 0 0 0 0* * * * * * * * highest quality band 1
* * * * * * * * * 0 0 0 0* * * highest quality band 2
etc...
Any help would be greatly appreciated. At this stage im plugging in the
decimal numbers into binary calculator and using r.reclass to create a
MASK.
best regards
Andrew
Glynn Clements <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
05/28/2007 09:14 AM
To
Hamish <[EMAIL PROTECTED]>
cc
grassuser@grass.itc.it
Subject
Re: [GRASS-user] help to use r.mapcalc with decimal/binary (modis data)
Hamish wrote:
> > Oops; I could have sworn that r.mapcalc understood hex. Sorry; you'll
> > need to use decimal values, e.g.
> >
> > r.mapcalc MASK="if(sur_refl_qc_250 & 240 == 176 , 1, null())"
>
> so r.mapcalc can do bitwise & |? (nothing about that in the help pages)
Damn, no, that neither.
Third attempt:
r.mapcalc MASK="if((sur_refl_qc_250 / 16) % 16 == 11 , 1,
null())"
I'll look at adding the missing functionality to r.mapcalc.
--
Glynn Clements <[EMAIL PROTECTED]>
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