Re: [las_users] LAS 8.6 error using Compute Average

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

Hi Penny,

The analysis operations - averaging, min, max, etc. as well as differences between variables or datasets use F-TDS to set up the new transformed variables. In order for these to work when datasets have init scripts, we're going to have to change the init scripts around a bit.

The change to init scripts is that we need to define a renaming for the variable name, and make the custom definition with the original name.

   SET DATA ($data_url)  
   set variable/name=varname_in varname
   let/d=1 varname = [_expression_ operating on varname_in]

So the example commands converting to Celsius, will look like this:

   SET DATA ($data_url)  
   set variable/name=analysed_sst_in analysed_sst
   let/title="Daily Sea Surface Temperature"/units="Celsius" analysed_sst = analysed_sst_in - 273.15

There is no longer the need to define the symbol DATA_VAR.   I've made a start at documenting this here, and we'll be getting more examples on that page.

There is also one change within LAS that is needed. Penny has the update but if anyone else needs this please contact us and we'll work out an update for you.

--Ansley

On 5/3/2017 11:08 AM, Oots, Penny C. (LARC-E3)[Science Systems & Applications, Inc.] wrote:

Yes, you have the correct aggregation.  Here is the full init script:

SET DATA ($data_url)

!<custom

let/title="Daily Sea Surface Temperature - GHRSST"/units="Celsius" analysed_sst_C = analysed_sst-273

DEFINE SYMBOL data_var =  analysed_sst_C

 DEFINE SYMBOL usedparam = "LAS  ($CURRENT_DATE) ($CURRENT_TIME) ($data_0_name)"

 MESSAGE/QUIET/CONTIN

On 5/3/2017 8:52 AM, Oots, Penny C. (LARC-E3)[Science Systems & Applications, Inc.] wrote:

Using Ferret 6.9.5 and LAS 8.6, a user reported what looks like an error or bug in computing averages over time using the https:/mynasadata.larc.nasa.gov Live Access Server.  

The user was calculating the average over time for Daily Sea Surface Temperature (GHRSST) under our category Oceans.  I was able to recreate the problem by plotting the individual SST data for Jan, Feb and Mar 2005.  The values for these plots on the color bar ranged from  -1.65 to 32.9 Celsius but when the average over time  was plotted, the range of values was –180 to 3157.   The values are also high when computing average over time.

The data is actually in Kelvin and is converted to Celsius using an init script containing the following:

let/title="Daily Sea Surface Temperature - GHRSST"/units="Celsius" analysed_sst_C = analysed_sst-273

DEFINE SYMBOL data_var =  analysed_sst_C

After commenting out the init script on the development server, the computed averages were still high.

Are other people seeing these kind of results also?

Penny Oots

SSAI, NASA Langley, Hampton, VA