Hi,
in this mail I would like to discuss a "mini" proposal, a new feature for
CSW (you tell me if you believe
it's going to be big enough to warrant a formal proposal): direct download
links for file based layers.
Direct downloads are a request we keep on seeing in the Metoc/EO world,
layers are based on complex NetCDF/Grib files, and the protocols we have to
output them, WCS in particular, are setup to allow slice, rescale,
reproject data, but not exactly to preserve the original data as is.
Certainly the data could be provided via FTP too, but it's combersome to
have to publish data twice, and it can be somehow hard to locate as FTP
provides no metadata at all.
So, for these layers, we would like to provide a direct download of the raw
data from CSW, that
makes the downloads searchable and there is already room foreseen in that
protocols for direct
download, via the "term-references" entry in dublin core metadata, and
OnlineResource in ISO
The idea would be that we create a link pointing back to the CSW service,
to a vendor request that will assemble the files for the requested
resource, zip them, and send the result back to the requestor, something
like:
http://host:port
/geoserver/ows?service=CSW&version=2.0.1&request=DirectDownload&resourceId=<layerName>
In order to locate the files we'd be using the information provided by
FileResourceInfo/FileServiceInfo, as discussed recently on geotools-devel.
Of course we would not automatically create those links, we'll have
configurations at the CSW level, and at the layer level as an override, to
allow direct download to be available.
Multidimensional Image mosaics are also of interest, and they add an
interesting twist: they are a aggregate resource, and we already expose the
granule of the mosaic in WCS-EO extended describe calls.
However, for direct downloads, we are looking not for the granules, but for
files, and when the mosaics are made of NetCDF/Grib files, the file
contains many granules.
So the idea is to have many download links associated to the mosaic, one
per file contained in it.
Now, there is a catch... how does the user find out which dimension ranges
are contained in each file? In ISO OnlineResource we could many abuse the
description field to stick some json payload describing the ranges, but it
would be ugly, and would not work for dublin core regardless.
So here is the idea: the link to the direct downolad will contain extra
parameters, not used by the DirectDownload method, that do describe the
file information ranges, something like:
http://host:port
/geoserver/ows?service=CSW&version=2.0.1&request=DirectDownload&resourceId=<layerName>:<fileName>&time=from/to&elevation=from/to&bbox=xmin,ymin,xmax,ymax&custDim=from/to
The link will contain dimensions represented as ranges to keep it brief, we
cannot build a url that contains all the single values, it would get too
long.
For completeness sake, we also thought about generating a stand alone
metadata record for each file in case of mosaics: it would have looked
good, but there is a serious catch, it would have broken big time record
paging, basically in order to discover what's at page 10 or the record list
one would have had to go, locate all resources that might have generated
extra records in the first 9 pages, expand them... making paging over CSW
unbearably slow.
So the idea, while nice from other points of view, got canned
Anyways... opinions?
Cheers
Andrea
--
==
Meet us at the INSPIRE Conference in Lisbon 25-29 May 2015! Visit
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==
Ing. Andrea Aime
@geowolf
Technical Lead
GeoSolutions S.A.S.
Via Poggio alle Viti 1187
55054 Massarosa (LU)
Italy
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