<br><font size=2 face="sans-serif">Dear All,</font><br><br><font size=2 face="sans-serif">i am having some issues with analysing
MOD09 modis data in grass. I would like to mask out the cloud
pixels using the below quality control band.</font><br><font size=2 face="sans-serif">when i import this band the unsigned
16bit integer is converted in decimal and I am unsure how to use
r.mapcalc to create a mask based on the different bits. </font><br><br><font size=2 face="sans-serif">I am unsure how I should go about this
(see *** section below). I would like to try different selections to see
which would make the best mask but i am unsure how to do this against a
binary field </font><br><br><font size=2 face="sans-serif">eg. r.mapcalc MASK="if(sur_refl_qc_250
== **** clear state **** , 1, null())"</font><br><br><font size=2 face="sans-serif">how do I select out the different bits
to create the mask?</font><br><br><font size=2 face="sans-serif">At this stage i am thinking of trying
to convert the decimal back to binary (not sure how to do this ) and then
subselect columns (bits) eg 0-1 or 2-3 and the placing an if statement
(eg. if column01 == "00" or if column23 = "00").</font><br><br><font size=2 face="sans-serif">Any guidance would be much appreciated.</font><br><br><br><font size=2 face="sans-serif">kind regards</font><br><br><font size=2 face="sans-serif">Andrew</font><br><br><br><font size=2 face="Arial"><b>sur_refl_qc_250m:</b> </font><br><font size=2><br></font><table width=100%><tr><td width=4% bgcolor=white><font size=2 face="Arial"><b>Bit</b></font><td width=95% bgcolor=white><font size=2 face="Arial"><b>Description</b></font><tr valign=top><td bgcolor=white><font size=2 face="Arial">0-1</font><td bgcolor=white><font size=2 face="Arial">MODLAND QA bits;<br>00 -- corrected product produced at ideal quality -- all bands<br>01 -- corrected product produced, less than ideal quality -- some or all
bands<br>10 -- corrected product not produced due to cloud effects -- all bands<br>11 -- corrected product not produced for other reasons -- some or all bands,
may be fill value<br>[Note that a value of (11) overrides a value of (01)]</font><tr valign=top><td bgcolor=white><font size=2 face="Arial">2-3</font><td bgcolor=white><font size=2 face="Arial">cloud state;<br>00 -- clear<br>01 -- cloudy<br>10 -- mixed<br>11 -- not set, assumed clear</font><tr valign=top><td bgcolor=white><font size=2 face="Arial">4-7</font><td bgcolor=white><font size=2 face="Arial">band 1 data quality, four bit
range;<br>0000 -- highest quality<br>1000 -- dead detector; data has been copied from adjacent detector<br>1001 -- solar zenith >= 86 degrees<br>1010 -- solar zenith >= 85 and < 86 degrees<br>1011 -- missing input<br>1100 -- internal constant used in place of climatological data for at least
one atmospheric constant<br>1101 -- correction out of bounds, pixel constrained to extreme allowable
value<br>1110 -- L1B data faulty<br>1111 -- not processed due to deep ocean or clouds</font><tr valign=top><td bgcolor=white><font size=2 face="Arial">8-11</font><td bgcolor=white><font size=2 face="Arial">band 2 data quality, four bit
range;<br>(same values as above)</font><tr valign=top><td bgcolor=white><font size=2 face="Arial">12</font><td bgcolor=white><font size=2 face="Arial">atmospheric correction performed;<br>0 -- no<br>1 -- yes</font><tr valign=top><td bgcolor=white><font size=2 face="Arial">13</font><td bgcolor=white><font size=2 face="Arial">adjacency correction performed;<br>0 -- no<br>1 -- yes</font><tr valign=top><td bgcolor=white><font size=2 face="Arial">14</font><td bgcolor=white><font size=2 face="Arial">different orbit from 500m;<br>0 -- no<br>1 -- yes</font><tr valign=top><td bgcolor=white><font size=2 face="Arial">15</font><td bgcolor=white><font size=2 face="Arial">unused (spare)</font></table><br><br><br><BR>
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