Data formats and data exchange protocols
- | OGC-WCS: The Open Geospatial Consortium develops and maintains the interface standard for interoperable protocols such as WCS (web coverage service), WFS (web feature service), and WMS (web map service). The current version of WCS is 1.1 (apparently, version 1.1.2 was deprecated recently due to the lack of a standard testing procedure). Version 2.0 is in preparation. The WCS 2.0 core specification is available, but this contains very limitied specific information on how the standard can actually be implemented. The relevant extensions (for example for netcdf encoding) are still awaiting a committee decision [July 2012]. A summary description how WCS works can be found here: Web Coverage Service (WCS)
- Network Common Data Format (netCDF): Netcdf is a binary file encoding format that allows to store attributes (i.e. metadata information) along with the data variables. For further information check out data model
General metadata specifications for geospatial information
These standards are mainly describing ways to specify the necessary information to find and access a specific data set, including for example information on the responsible contact person. Technically, this is implemented with XML documents that can be validated against XML schema files. The international standard for describing geospatial metadata is ISO 19115. The implementation of ISO 19115 is described in ISO 19139. In Europe, the INSPIRE directive (see ) is establishing another standard, which is largely compatible with ISO19115, but in some areas less and in other areas more stringent (concerning required metadata). Unfortunately, ISO documents are not freely available. However, it is possible to find a good part of information about it on the internet.
- ISO 19139 codelists: These codelists contain the controlled vocabulary defined by ISO 19139
- NOAA GEO-IDE Metadata and Coverages and netcdf attribute convention for dataset discovery including its conformance test at | C-Test. A helpful introduction to ISO metadata is available at ISO Building Blocks
- INSPIRE Implementing Rules provides access to INSPIRE documents including metadata legislation and guidance documents, data specifications, etc.
- [| Climate and Forecasting (CF)] metadata conventions: These metadata conventions are very different from ISO 19115 and INSPIRE in that they establish a standard for describing the information content in a data file (whereas ISO and INSPIRE describe information about a file or service). Nevertheless, there is a close relation between the two: firstly, the information should be consistent, secondly, information contained in the file can be harvested to (automatically) create XML metadata files which should then follow the ISO (and INSPIRE) rules.
- AQ Community metadata "facets" discussion on Solta: In order to enable the air quality data network, the initial approach has been to define so-called metadata facets based on the content requirements that were seen as essential for the dataset discovery (see for example the Core.uFind catalogue at WUSTL or the ACTRIS catalogue at NILU. These metadata facets are not necessarily compliant with the ISO or INSPIRE standards (and they may be incomplete). Discussions to extend the thematic information that should be available in metadata records and how thi sinformation can be mapped onto the existing ISO and INSPIRE standards are at the heart of the GEo AQ CoP Dublin workshop 2012.
Tools for handling (ISO and INSPIRE) metadata
There are commercial and free metadata editors available which include schema specifications for ISO19115 and INSPIRE. The INSPIRE Geoportal also makes a metadata editor and validator available.
- CatMDEdit is an open source metadata editor which is farily straightforward to use and can at least help to obatin a better understanding of the ISO 19115 and INSPIRE metadata structures (see example at ISO_INSPIRE_Metadata_Structure).
Data set type specific issues
- atmospheric models generally use a spherical lat/lon coordinate system. There is a need to define the appropriate coordinate reference system (CRS) in the associated metadata. Terms that are often seen in this context are "WGS84" and "urn:ogc:def:crs:OGC:2:84" or "urn:ogc:def:crs:EPSG::4326". An email exchange with EPSG on this provides some further input to this discussion.