Changes between Version 3 and Version 4 of udg/ecoms/dataserver/web

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Timestamp:
Jun 13, 2013 11:04:05 AM (9 years ago)
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 v3 Afterwards, the different datasets described in [#s.thredds TDS section] are listed as links in the web browser window. [[Image(fig01.png,align=center,width=320px,title=Catalog of the EUPORIAS-SPECS System4 datasets. Note that although they only include a few variables, their size range from one to four Terabytes)]] [[Image(fig01.png,align=center,width=520px,title=Catalog of the EUPORIAS-SPECS System4 datasets. Note that although they only include a few variables, their size range from one to four Terabytes)]] By clicking in any of the datasets, a new window will appear providing information on the variables and geospatial and time coverages, and offering different options for data access and/or visualization. [[Image(fig02.png,align=center,width=320px,title=Detail of a particular dataset with information on the included variables and geospatial and time coverages. The different options for data access and visualization are also shown.)]] [[Image(fig02.png,align=center,width=520px,title=Detail of a particular dataset with information on the included variables and geospatial and time coverages. The different options for data access and visualization are also shown.)]] Currently, only the OPeNDAP access service is fully operative in the portal. Therefore, in this example, we will illustrate the use of this service, which allows selecting time/spatial data slices from the OPeNDAP data access form shown in figure and downloading the resulting data in both ''ASCII'' and ''Binary'' formats. [[Image(openDAPwindow.png,align=center,width=320px,title=Detail of the OPeNDAP dataset access form for a particular dataset.)]] [[Image(openDAPwindow.png,align=center,width=520px,title=Detail of the OPeNDAP dataset access form for a particular dataset.)]] Note that, as explained before, the variables provided by the data portal (e.g. minimum temperature) are stored as gridsets. Thus, in addition to these variables, also auxiliary coordinate variables (lat, lon, run, time, member) should be handled for geo-temporal data referencing ([attachment:openDAPwindow.png see Figure]). Moreover, three time coordinates are included as referece for different grid variables because they are defined for different forecast times (one extra time for precipitation and different temporal resolution for mean sea level pressure). Note that this highly complicates the direct analysis of the data and, hence, this options is only recommend for data exploration. In the following we show how to use this service to explore the structure of the datasets and to obtain simple pieces of information in ASCII format. The main disadvantage of the OPeNDAP service from the end-user point of view is that the specifications for subsetting dimensions are not given in their original magnitudes (i.e., latitudes and longitudes are not given in decimal degrees), but by the indexes of their position along their respective axes (note that first index value is always 0). Thus, to find out the indexes for the desired selection, we need to dump and analyze the particular values defined in the coordinate variable. For instance, this figure shows the 241 values defined for the lat (latitude) coordinate, as provided by the ''Get ASCII'' option (selecting the corresponding check-box). [[Image(latlonDump.png,align=center,width=320px,title=Text file displaying the values for the lat (latitude) coordinate variable.)]] [[Image(latlonDump.png,align=center,width=520px,title=Text file displaying the values for the lat (latitude) coordinate variable.)]] Using these facilities it can be obtained after some calculations that the closest lat and lon coordinates for a particular location of interest (e.g. Madrid) are 66 and 475, respectively. Thus, the time series for Madrid corresponding to the example described in the previous section (minimum temperature forecasts for January with one-month lead time, i.e. from the simulations started the first of December) could be requested as shown in Figure [[Image(opendapquery.png,align=center,width=320px,title=Detail of the query from the OPeNDAP dataset access form to retrieve a subset (a time series for a single gridbox) of minimum temperature.)]] [[Image(opendapquery.png,align=center,width=520px,title=Detail of the query from the OPeNDAP dataset access form to retrieve a subset (a time series for a single gridbox) of minimum temperature.)]] Note that the indices selected for the run coordinate correspond to the December initilizations (index positions 11, 23,...; note that indexes start in 0) and for the time coordinate correspond to January (positions, 31 to 62, in days after the run time). Note that the proper use of this service requires a full understanding of the data structure and, therefore, it is only advised for data exploration. Note that the indexes selected for the run coordinate correspond to the December initializations (index positions 11, 23,..., and that indexes start in 0) and for the time coordinate correspond to January (positions, 31 to 62, in days after the run time). The proper use of this service requires a full understanding of the data structure and, therefore, it is only advised for data exploration.