Re: [thredds] Scan Aggregation vs. Feature Collection

Hi Kyle:

For GRID data aggregations, If they are GRIB format, use Feature Collection, type=GRIB. Otherwise use type=FMRC, even if theres only one runtime. Let us know any problems.


On 10/3/2012 10:09 AM, Kyle Wilcox wrote:
Hi John -

Just trying to clarify a few things when testing 4.3:

If we have a homogenous set of non-forecast GRID FeatureTypes (satellite), we 
should still use an 'old-style' NcML aggregation because there is no GRID 

If we have a heterogeneous set of non-forecast GRID FeatureTypes (satellite 
passes on slightly different grids), there is currently no way to aggregate 
them in 4.3 because there is no GRID FeatureCollection.

Thanks ,

-----Original Message-----
From: thredds-bounces@xxxxxxxxxxxxxxxx [mailto:thredds-
bounces@xxxxxxxxxxxxxxxx] On Behalf Of John Caron
Sent: Monday, July 23, 2012 5:50 PM
To: Roy Mendelssohn
Cc: thredds@xxxxxxxxxxxxxxxx
Subject: Re: [thredds] Scan Aggregation vs. Feature Collection

Well, its complicated.

Old style aggregations, aka "NcML aggegations" remain supported. I think of
these as low level index manipulations. These are embedded in NcML, either
on the client or in TDS config catalog, see:

We can do much better when we know the "feature type", and the new way is
called "feature collections":

1) type=FMRC is for gridded data. Works mostly of in 4.2, but refactored in 4.2
and still testing.
2) type=GRIB is for GRIB data, which is a special kind of gridded data.
This supersedes FMRC when the data is in GRIB. Only in 4.3, ready for beta
3) type=point are for point feature types. Still in alpha in 4.3

NcML works fins when you know what you are doing and you have
homogenous files. feature collections are intededd to be easier to use and
tolerate heterogeneous files.


On 7/23/2012 3:27 PM, Roy Mendelssohn wrote:
But is this just for FMRC aggregation, or for all aggregations?  I could swear I
remember a web age with feature collections that "grid" was a feature type,
but when I looked the other day, it was point, station and grib I believe.
Maybe it was my old age and bad vision seeing "grid" for "grib".  If there is an
aggregation for featureType=grid, can you point me to the page that describes

We do not have any FMRC aggregations, but if there all of our aggregations
should be feature collections, then I have a lot of editing to do on our xml



On Jul 23, 2012, at 1:59 PM, John Caron wrote:

On 7/19/2012 11:50 AM, Roy Mendelssohn wrote:
Hi All:

I have asked this before and am not certain that I ever got a response.
For TDS 3.0 is it correct to assume that scan aggregation is deprecated and we
should be using feature collections for aggregation instead?
Hi Roy:

Yes correct, though we are still debugging the FMRCs in 4.3.

For GRIB files, you really want to use feature collections , type = GRIB.

4.3.12 is the last alpha, next release will be beta. It should be ready this

Would appreciate use and feedback.


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