Thank you for the links that helped to understand more how the things are working within GRASS.
For the moment I decided to use r.mapcalc QA_field1="(QA>>bit_position_field1)% bit_length_field1" for the different fields and then combining the files obtained into a mask. Thanks Laura 2009/6/15 Hamish <[email protected]> > > Laura Poggio wrote: > > I am trying to use the QA information of MODIS products. I > > found that this analysis can be done in GRASS with > > r.bitpattern (from Neteler, 2005 with some examples) > > or with r.mapcalc . > > > > From what I understood, the use of r.mapcal seems to be > > more flexible. I am just wondering if there are some code > > examples using the bitwise operators of mapcalc. > > this doesn't answer your question directly, but maybe it is of > interest: > http://grass.osgeo.org/wiki/MODIS > > and quality layer application method here > http://grass.osgeo.org/wiki/AVHRR > > > > Hamish > > > From what I understood, the use of r.mapcal seems to be more flexible. > > I am just wondering if there are some code examples using the bitwise > > operators of mapcalc. I found the following code: > > "lst_filt = (lstmap ~ [XX XX XX 00]) || (lstmap ~ [XX XX 0X 01])" > > but to me it is not really clear how this works, especially compared > > to the code provided (and explained) by Glynn Clements: > > r.mapcalc MASK="if((sur_refl_qc_250 / 16) % 16 == 11 , 1, null())" > > > > Thank you very much for any help. > > > > Laura > > > 2009/6/15 Nikos Alexandris <[email protected]> > >> Hi Laura! >> >> I am sending you some notes of mine off-list. Also, check... >> >> "In the upcoming release of GRASS (version 7) there is an extra module >> to derive such quality layers called i.modis.qc" ; >> >> Yann Chemin, International Rice Research Institute, The Philippines, >> http://svn.osgeo.org/grass/grass/trunk/imagery/i.modis.qc/i.modis.qc.html >> >> Regards, Nikos >> > >
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