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Yaqian,<br>
<br>
I think you need to specify all ranges for each file since the grids
are different. You only define the lat/lon based on the first file
(GIMMS). To be safe you should set the lat/lon/z/t for each data
set. So, add the 'set lat 13 20' and 'set lon -15 20' after 'set
dfile 2' to ensure your two grids are the same.<br>
<br>
Jim<br>
<br>
<div class="moz-cite-prefix">On 6/20/14 3:48 AM, Yaqian He wrote:<br>
</div>
<blockquote
cite="mid:CAKbvkVUoE2W9SFOo2dSdUL7E5n1RT4VNEmaruB4E9c_V8jZVLQ@mail.gmail.com"
type="cite">
<div dir="ltr">Hi,<br>
<div class="gmail_quote">
<div dir="ltr">
<div>
<div>
<div><br>
</div>
I want to calculate the average seasonal (Dec to Feb)
mean difference between GIMMS and MODIS NDVI, here is
script I wrote:<br>
<br>
'reinit'<br>
*gimms<br>
'sdfopen /Users/geog493/ndvi/<a moz-do-not-send="true"
href="http://ndvi0.5deg.2006.nc" target="_blank">ndvi0.5deg.2006.nc</a>'<br>
'sdfopen /Users/geog493/ndvi/<a moz-do-not-send="true"
href="http://ndvi0.5deg_modis_westafrica.nc"
target="_blank">ndvi0.5deg_modis_westafrica.nc</a>'<br>
'set lat 13 20.0'<br>
'set lon -15.0 20.0' <br>
* DJF<br>
'define gy01=ave(ndvi.1,t=467,t=472)' <br>
'define gy02=ave(ndvi.1,t=491,t=496)'<br>
'define gy03=ave(ndvi.1,t=515,t=520)'<br>
'define gy04=ave(ndvi.1,t=539,t=544)' <br>
'define gy05=ave(ndvi.1,t=563,t=568)'<br>
'define gy06=ave(ndvi.1,t=587,t=592)' <br>
'define gyclim=(gy01+gy02+gy03+gy04+gy05+gy06)/6.'<br>
*'modis ndvi'<br>
'set dfile 2'<br>
'set t 1 307'<br>
* DJF<br>
'define my01=ave(ndvi.2,t=15,t=20)' <br>
'define my02=ave(ndvi.2,t=38,t=43)'<br>
'define my03=ave(ndvi.2,t=61,t=66)'<br>
'define my04=ave(ndvi.2,t=84,t=89)' <br>
'define my05=ave(ndvi.2,t=107,t=112)'<br>
'define my06=ave(ndvi.2,t=130,t=135)'<br>
'define myclim=(my01+my02+my03+my04+my05+my06)/6.'<br>
'define difyclim=gyclim-myclim'<br>
'd gyclim-myclim'<br>
<br>
</div>
However, it always shows the error "Error in gagchk: axis
sizes are not the same<br>
Operation error: Incompatable grids"<br>
<br>
</div>
<div>The two datasets have the same resolution (0.5X0.5),
the original information for the two datasets are:<br>
modis<br>
xdef 81 linear -20 0.5<br>
ydef 81 linear 0 0.5<br>
gimms<br>
xdef 720 linear -179.75 0.5<br>
ydef 304 linear -61.75 0.5<br>
</div>
<div> Are there something wrong here? Could you help me?<br>
<br>
</div>
<div>Thanks in advance!<br>
<br>
</div>
<div>Best wishes!<span class="HOEnZb"><font color="#888888"><br>
</font></span></div>
<span class="HOEnZb"><font color="#888888">
<div>Yaqian<br>
</div>
</font></span></div>
</div>
<br>
</div>
<br>
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<br>
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</blockquote>
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