6

For geographic vector data (Features) there is an OGC standard that defines geometries and their different annotations such as WKT and WKB.

For raster image data however, I was not able to find comparable standards. PostGIS uses something like WKB represenations in their PostGIS Raster, but even for the PostGIS raster I did not find a document that would describe the Raster Type other than the PostGIS manuals which are more user oriented and do not explain the standard in the same way as a standardization document would.

Does anyone know if there is such a standard for Raster?

Links to detailed definitions of the PostGIS raster would also be useful here if there is no standard.

3

Good question and not one I've really given thought to before. This might be the sort of thing you're interested in:

Some searching show's that there's ISO19123:2005 - "Geographic information -- Schema for coverage geometry and functions" - needless to say, being an ISO standard it's decidedly not "Open" - they cost a small fortune to access - http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=40121

ISO 19123:2005 defines a conceptual schema for the spatial characteristics of coverages. Coverages support mapping from a spatial, temporal or spatiotemporal domain to feature attribute values where feature attribute types are common to all geographic positions within the domain. A coverage domain consists of a collection of direct positions in a coordinate space that may be defined in terms of up to three spatial dimensions as well as a temporal dimension.

There's also the GML 3.2.1 Application Schema for Coverages - http://www.ogcnetwork.net/node/1592 which:

has been developed jointly by the GML, WCS, and SWE groups, defines OGC's unified coverage model. GML serves both as conceptual model, ensuring a concisely defined semantics, and as one of many possible encoding formats. This way, coverages can be transported across different services, such as WCS, WCPS, WPS, and SOS.

As you can guess, being GML based, they're both rather verbose unlike WKT.

  • Please remember that open and free are different things :-) – Ian Turton Jan 14 '15 at 11:58
  • @iant - Fair point. Wikipedia goes into some length to basically say "everyone has a different definition of open-ness" - en.wikipedia.org/wiki/Open_standard – GIS-Jonathan Jan 14 '15 at 12:29
  • Rasters are basically just X and Y coordinates and an attribute value M at that location with one or more bands. There are loads of image standards about how to save this information into database or files. Some standards are open (png, tiff, gif, jpeg), some proprietary (ECW, MrSID) but what makes formats different is mainly the use of compression and indexes and how the X-Y-M information is encoded into binary code. Some organizations have defined which formats they accept (NITF, INSPIRE inspire.jrc.ec.europa.eu/documents/Data_Specifications/…). – user30184 Jan 14 '15 at 13:59
  • Thanks Jonathan the GML standard is along the lines of standards I was looking for. @user30184 - I have not thought of the image formats as raster standards, but I guess they can be considered as standards for some of the formats that allow GIS metadata. However, for my use-case those formats are too complex. Ultimatively I was looking for a simpler and truely GIS focused standard that is not as verbose as GML. – yellowcap Jan 14 '15 at 15:02
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For PostGIS' implementation, see these documents that describe the WKB formats for raster data. Similar is also documented here. There is no text equivalent for this data that I'm aware of, despite early naming of the effort as "WKTRaster".

As for OGC, they retired their Grid Coverage Service standard which defined things like "WKBGeoTIFF".

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