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[GEMPAK #RIA-330971]: Ship position rounding via dcmsfc

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  • Subject: [GEMPAK #RIA-330971]: Ship position rounding via dcmsfc
  • Date: Fri, 26 Sep 2014 14:32:34 -0600
> The following is a comparison of ship positions for NOAA Pisces (WTDL)
> from hourly ship data decoded using gempak (real time via ldm) and that
> from high resolution data obtained from the vessel's support staff
> recently for a mission off the coast of FL in August 2013. Gempak data
> are reported to 0.01 deg resolution. It appears that the a rounded
> position from the ship high resolution data would  be nearly
> consistently west by .01 degree in longitude (not assessing that
> latitude offset). This makes me wonder if there is a problem with the
> "rounding" in the gempak decoder. Can this be verified?

Hi Mike,

This is interesting. High resolution I think is the key here.  I took some real 
time ship reports (WMO header SMVD) and found the lat and lon resolution of 
0.01 degree, so while GEMPAK does convert a REAL to INT, in the case of ship 
reports the input lat and lon are already rounded or truncated to 0.01 
resolution.   It appears that dcmsfc is decoding the position accurately and 
that the WMO reports are where the rounding occurs.  

Michael James
Unidata Program Center
Boulder, CO

Ticket Details
===================
Ticket ID: RIA-330971
Department: Support GEMPAK
Priority: Normal
Status: Open