Re: [las_users] LAS unable to catch errors

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi Upendra,
Thank you for the report, and I understand your concern. When LAS reads this time series (via Ferret), the software is not returning any error code, so LAS doesn't have any way to report that anything is wrong.  In general, I would say that if you see errors such as

  Malformed or inaccessible DAP DATADDS 

with any slice of a dataset, it's an indication of problems with the dataset or aggregation or the thredds server (as you know).

However I can do a few things to check into this.

Following the Info link from this dataset in your LAS, the URL for the data is shown to be
http://data.nodc.noaa.gov/thredds/dodsC/pathfinder/testdata/crw/oa_data/aggregations/yearly_aggregate_2000.ncml

If I look at that URL directly in Ferret, using the latest official release of Ferret,  I see the kind of thing that's showing up in your LAS. This version of Ferret is linked with NetCDF4.1.1 for reading NetCDF files and OPeDNAP url's.  Here are the Ferret commands to list the NetCDF version, and list a time series from the data.  The netCDF library is making a data request, and data is read from the URL without any error flags.

yes? show symbol netcdf*
NETCDF_VERSION = "4.1.1 of Sep 16 2010 10:42:11 $"

yes? use "http://data.nodc.noaa.gov/thredds/dodsC/pathfinder/testdata/crw/oa_data/aggregations/yearly_aggregate_2000.ncml"

yes? list/x=60w/y=22 pH
             VARIABLE : NOAA Coral Reef Watch Experimental Ocean Acidification Product Suite - pH 25km (Total Scale)
             DATA SET : Archived NOAA Coral Reef Watch  25km Ocean Acidification Product Suite for the Greater Caribbean Region -monthly, 2000
             FILENAME : yearly_aggregate_2000.ncml
             FILEPATH : http://data.nodc.noaa.gov/thredds/dodsC/pathfinder/testdata/crw/oa_data/aggregations/
             SUBSET   : 12 points (TIME)
             LONGITUDE: 60.1W
             LATITUDE : 21.9N
                    60.13W
                    121
 15-JAN-2000 /  1:   82.2
 14-FEB-2000 /  2:  257.0
 16-MAR-2000 /  3:   82.4
 15-APR-2000 /  4:  151.1
 16-MAY-2000 /  5:   82.2
 15-JUN-2000 /  6:  295.5
...

When the same Ferret code is linked with the most-recent beta NetCDF library, I see what looks like to be the correct result

yes? show symbol netcdf*
NETCDF_VERSION = "4.1.2-beta2-snapshot2011010522 of Jan  6 2011 10:14:32 $"

yes?  use "http://data.nodc.noaa.gov/thredds/dodsC/pathfinder/testdata/crw/oa_data/aggregations/yearly_aggregate_2000.ncml"

yes? list/x=60w/y=22 pH
...
             SUBSET   : 12 points (TIME)
             LONGITUDE: 60.1W
             LATITUDE : 21.9N
                    60.13W
                    121
 15-JAN-2000 /  1:  8.100
 14-FEB-2000 /  2:  8.100
 16-MAR-2000 /  3:  8.100
 15-APR-2000 /  4:  8.100
 16-MAY-2000 /  5:  8.100
 15-JUN-2000 /  6:  8.100
...

So it seems that the upcoming netCDF4.1.2 release does something that is more robust with respect to whatever is wrong with the dataset. Unidata is planning a release of netCDF4.1.2 very soon, and we will be releasing a new version of Ferret which will be linked with that.

Ansley

On 1/7/2011 11:02 AM, Upendra Dadi wrote:

Hi,

On 1/7/2011 11:02 AM, Upendra Dadi wrote:

Hi,
 I have a dataset which is not being read properly by THREDDS due to some issues with the file holding the dataset. But when plotting a time-series graph involving a data point from this file, it still generates a graph. But the plot is wrong. I am not sure where LAS is getting data for this plot. As an example, choose the following dataset from http://data.nodc.noaa.gov/las/getUI.do :
 NODE > Archived NOAA Coral Reef Watch 25km Ocean Acidification Product Suite.... > Aggregation by year > 2000 > pH 25km

When plotting the latitude-longitude map for April with this dataset, I get an error (though the error message itself doesn't seem to be representative of the problem).  But when plotting time series plot, it doesn't give any error message. But, the values in the plot are wrong. The pH values as far as I know should be between 0-14, but the plot shows that the values are between 80 and 300. You will also see that the latitude-longitude maps for all other months is fine. Apparently, the problem is occurring due to data from the month of April. LAS is not catching the problem.

The solution for me would be to replace the dataset on THREDDS with correct datasets. I just wanted to let you know anyway since LAS is not catching the problem.

Upendra