[thredds] Stride not working with ncml aggregation

• To: thredds@xxxxxxxxxxxxxxxx
• Subject: [thredds] Stride not working with ncml aggregation
• From: Upendra.Dadi@xxxxxxxx
• Date: Fri, 01 Jul 2011 11:27:54 -0400

Hi,
  I am getting wrong results with OpenDAP requests on ncml aggregation when 
using strides. THREDDS sometimes give an error message and sometimes the output 
is plain wrong.  It seems to be working fine with regular netCDF files. 
To demonstrate this I have created two files  the first file is a regular 
netcdf file with one variable (with name "time") and one dimension of size 14:
  
http://data.nodc.noaa.gov/thredds/catalog/testdata/strides/catalog.html?dataset=testdata/strides/agg.nc
The values for the variable range from 1 to 14.

The second is an ncml aggregation which is equivalent to the first file, 
aggregated along the single dimension. The ncml aggregation has four files- 
first file with dimension 5, second with 3, third with 2 and fourth with 4 
(adds up to 14):
  
http://data.nodc.noaa.gov/thredds/catalog/testdata/strides/catalog.html?dataset=testdata/strides/agg_thredds.ncml

Now, when I issue OpenDAP requests with strides, I get the following output

Request                                Output from the regular NetCDF           
                  Output from the NCML aggregation(- - - - - | - - - | - - | - 
- - -)
------------                               
---------------------------------------------                            
-------------------------------------------------
time[0:1:13]                    1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14   
                1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14    (correct)
time[0:2:13]                                    1, 3, 5, 7, 9, 11, 13           
                                                   1, 3, 5, 7, 9, 11, 13        
            (correct)
time[0:3:13]                                         1, 4, 7, 10, 13            
                                                            1, 4, 8, 12, 0      
                   (incorrect)
time[0:4:13]                                            1, 5, 9, 13             
                                      message = "NcSDArray 
java.lang.ArrayIndexOutOfBoundsException=null for request= NcSDArray read time 
time(0,4,13) ... 
time[0:5:13]                                              1, 6, 11              
                                                                     1, 6, 11   
                          (correct)            
time[0:6:13]                                               1, 7, 13             
                                                                      1, 0, 0   
                           (incorrect)
time[0:7:13]                                                 1, 8               
                                                                          1, 0  
                               (incorrect)
time[0:8:13]                                                 1, 9               
                                                                          1, 9  
                               (correct)
time[0:9:13]                                                 1, 10              
                                                                         1, 0   
                              (incorrect)
time[0:10:13]                                               1, 11               
                                                                        1, 11   
                           (correct)
time[0:11:13]                                               1, 12               
                                                                        1, 0    
                            (incorrect)
time[0:12:13]                                               1, 13               
                                                                        1, 0    
                            (incorrect)
time[0:13:13]                                               1, 14               
                                                                        1, 0    
                            (incorrect)
time[0:14:13]                                                 1                 
                                                                             1  
                                (correct)

There seems to be some pattern to whenever it gives incorrect results.  After 
jumping from one dataset to a subsequent one in the aggregation, if the new 
index doesn't correspond to the first value in the subsequent dataset, it gives 
incorrect results. 

Upendra

• Follow-Ups:
  • Re: [thredds] Stride not working with ncml aggregation
    • From: John Caron