[gradsusr] GDS date-time standard

[James T. Potemra]

Hi all:

I'm wondering if anyone knows how GDS derives a date-time value from a 
GrADS style binary file?  For example, a contributed data set could have 
a descriptor file with a TDEF defining a start-date of Jan 1, 2013 and 
increment of 1dy.  If this file were served via GDS, the OPeNDAP 
date-time becomes "days-since-1-1-1".  In experimenting with some 
GDS-served files, it seems that this conversion is off by two days.

Here's an example.  The following is daily measurements from QUIKSCAT:
http://apdrc.soest.hawaii.edu:80/dods/public_data/satellite_product/QSCAT/qscat_daily

The data descriptor file has the following:
TDEF 3776  linear  20JUL1999  1DY

and the DDS page seems to have the correct values for time:
*time*: 	Array of 64 bit Reals [time = 0..3775]
grads_dim: "t"
grads_mapping: "linear"
grads_size: "3776"
grads_min: "00z20jul1999"
grads_step: "1dy"
units: "days since 1-1-1 00:00:0.0"
long_name: "time"
minimum: "00z20jul1999"
maximum: "00z19nov2009"
resolution: 1.0


However, the OPeNDAP supplied first time-step is 729956 (obtained either 
through python call or ncdump).  I think that this corresponds to July 
22, 1999 rather than the actual July 20, 1999 as defined in the 
descriptor file.

Can anyone comment on what's going on here?  I found the same behavior 
with two other daily files, same apparent 2-day off-set. Thanks,

Jim
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://gradsusr.org/pipermail/gradsusr/attachments/20131007/b4edba3b/attachment.html