[GRASS-user] bitpattern analysis

[Laura Poggio]

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 <hamish_b at yahoo.com>

>
> 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 <nikos.alexandris at felis.uni-freiburg.de>
>
>> 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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