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 Planned 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