Re: [thredds] Constraint expression when choice of longitudinal extent spans prime meridian

• Subject: Re: [thredds] Constraint expression when choice of longitudinal extent spans prime meridian
• From: ashwinD12 <winash12@xxxxxxxxx>
• Date: Sun, 19 Jun 2016 11:43:42 +0530

I  finally settled with this algorithm for queries that span the prime
meridian. If incorrect - please go ahead and comment

Assume minLon and maxLon are the longitudinal extent for input to THREDDS
server(assume 0 to 360 range)

Step 0  Calculate difference between maxLon and minLon

Step 1 - if difference of longitude (min lon, max lon) is greater than 180


Step 2 -  Form two constraint expression with  these extents - [0:minLon]
and [maxLon:357.5]


Step 3 - Send two queries to THREDDS server and combine the results of the
two into one file.



On Fri, Jun 3, 2016 at 9:30 PM, Roy Mendelssohn - NOAA Federal <
roy.mendelssohn@xxxxxxxx> wrote:

> Hi Ashwin:
>
> Well that is almost correct, it depends on how the data are setup.  Th
> more accurate statement is that the query can not loop around any of the
> coordinate bounds. If the prime meridian is one of the longitude limits ,
> than you can not cross it in a request.  but if it is not on the boundary
> than it can be crossed.  So if a dataset has longitudes (0,360) you can’t
> cross it, but if it is (-180,180) you can, but you can’t cross the dateline.
>
> -Roy
>
>
>
> > On Jun 3, 2016, at 8:44 AM, ashwinD12 . <winash12@xxxxxxxxx> wrote:
> >
> > Hello,
> >            I had an associate of mine inform me that when an OpenDAP
> expression's longitudinal extent spans the prime meridian then we must
> query the data on both sides of the prime meridian and join the results. Is
> that accurate ?
> >
> > Regards,
> > Ashwin.
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• References:
  • [thredds] Constraint expression when choice of longitudinal extent spans prime meridian
    • From: ashwinD12 .
  • Re: [thredds] Constraint expression when choice of longitudinal extent spans prime meridian
    • From: Roy Mendelssohn - NOAA Federal