PostGIS WKT Raster Home Page

Quick Links

• Planning & Funding

• Beta 0.1.6 Working Specifications
• Beta 0.1.6 Final Specifications
• Beta 0.1.6 Documentation

• Beta 0.2.4 Working Specifications
• Working Specifications for Future Versions

Welcome to the WKT Raster project home page!

PostGIS WKT Raster is an ongoing project aiming at developing raster support in PostGIS. It is a new project very different from the previous PGRaster project and also very different from ​Oracle Spatial GeoRaster.

The goal of WKT Raster is to implement the RASTER type as much as possible like the GEOMETRY type is implemented in PostGIS and to offer a single set of overlay SQL functions (like ST_Intersects) operating seamlessly on vector and raster coverages.

Development Info

• Planning - Beta 0.1.6 PostGIS WKT Raster should happen by september 2009. Look at the planning page for a detailed schedule and to know how to contribute.

• Specifications - To know more about or contribute your ideas about the design of WKT Raster consult the working specification page. Accepted specifications are aggregates into the final specification page.

• Source Code - PostGIS WKT Raster source code is available from the OSGeo Subversion repository at ​https://svn.osgeo.org/postgis/spike/wktraster

• PowerPoint - Original Project Presentation - rationale, examples and preliminary specifications: ​PPT, ​PDF (v1.0)

• More Info - For more details and examples of application:
  
  
  • Search for "WKT Raster" in the ​PostGIS mailing list archive or in ​Nabble
  • Write to ​Pierre Racine

Overview of PostGIS WKT Raster Functionalities

WKT Raster…

…is as simple as PostGIS…

• one table = one raster coverage (like a vector coverage)
• one row = one tile or one raster object (like a vector coverage where one row = one geometry)
• only one new type: RASTER (like the PostGIS GEOMETRY type)
• each raster tile has a pixel size, a width and a height, a variable number of band, a pixel type per band and a nodata value per band. Everything essential to do base raster GIS operations.

…is an extension of PostGIS to be installed separately

• merge with PostGIS might occur in the future…

…has an import/export mechanism similar to shp2pgsql

• raster2pgsql and pgsql2raster utilities allowing import/export of a single raster or a batch of raster into a tiled coverage.

…allows easy conversion from/to geometry/raster…

• RT_AsPolygon(raster) → geometry
• RT_AsRaster(geometry, pixelsize) → raster

…implements base GIS raster operations available in most GIS…

• RT_Resample(raster, pixelsize, method) → raster
• RT_Clip(raster|geometry,geometry) → same type as first argument
• RT_Reclass(raster|geometry,string) → same type as first argument
• RT_MapAlgebra(raster|geometry, raster), mathematical expression, "raster"|"geometry") → raster/geometry
• etc…)

…introduces raster/geometry seamless geometry constructors…

• so you don't have to bother whether the layers are in raster or vector form when using analysis functions.
• RT_Intersection(raster|geometry, raster|geometry, "raster"|"geometry") → raster/geometry
• RT_Union(raster|geometry, raster|geometry, "raster"|"geometry") → raster/geometry
• RT_Accum(raster set|geometry set, "raster"|"geometry") → raster/geometry
• RT_Transform(raster|geometry, SRID) → same type as input
• etc…

…and seamless geometry operators…

• RT_Intersects(raster|geometry, raster|geometry) → boolean
• RT_Contains(raster|geometry A, raster|geometry B) → boolean
• etc…

…allows raster storage INSIDE the database (as WKB) for efficient overlay analysis operations between vector and raster layers…

…or OUTSIDE the database (as JPEG or TIFF) so desktop and web applications can quickly access and load raster tiles and nevertheless benefits from the powerful PostGIS GiST spatial index. Every WKT Raster SQL functions working with in-db raster tiles work seamlessly with out-db raster tiles.

…introduces the concept of raster objects…

• geographic features are stored as variable size raster tiles instead of polygons.
• allows vector to raster conversion without lost of information.

…is much more simple than PGRaster and Oracle GeoRaster. WKT Raster supports…

• only one type (instead of two: SDO_GEORASTER & SDO_RASTER). In WKT Raster there is no differences between a raster and a tile: a tile is a raster and a raster is a tile. A coverage is a table of tiles.
• no metadata (like PostGIS).
• no masks (you can build a mask as a band).
• no multiple dimensions (only two: x, y). Not to be confused with bands; WKT Raster DO supports multiband raster…
• no pyramids (reduced resolution coverages can be stored as a separate layer).

What do people think about WKT Raster?

​Paul Ramsey:

This proposal is better than any I have seen, addresses solving problems that if solved will provide actual new functionality and benefit to users, and clearly you've thought this through over some time

​Regina Obe:

The functions WKT Raster proposes look pretty cool actually and my vision of the benefits of storing raster in the database are covered in it