We just finished the first draft of the last chapter of our book: First look at PostGIS WKT Raster. This completes our hard-core writing and now on to more drafting,
polishing all the chapters.
In Chapter 13 we demonstrate how to use PostGIS WKT Raster functions by example and cross breed with PostGIS geometry functionality. I was pleasantly surprised to see how nicely the raster and geometry functions play together.
We had intended this chapter to be short about 20 pages in length, because how much can one say about pixels and pictures. As it turns out, a lot.
Rasters are more versatile than their picture portrayal on a screen. Rasters are a class of structured storage suitable for representing any numeric,
cell based data where each cell has one or more numeric properties (the bands). This covers quite a bit of data you collect with remote sensing and other electronic instrumentation. We had to stretch to over 30 pages; even then we felt we were missing some critical examples.
There is a lot of useful functionality in PostGIS WKT Raster
already and should make a lot of people looking for raster support in PostgreSQL very happy. Although the chapter may portray some scenes of violence and torture inflicted on elephants, you can rest assured
that it is pure illusion and no real elephants or blue elephant dolls were harmed in the making of this chapter.
As a side note -- our book is now listed on Amazon PostGIS in Action.
It is not available in hard-copy yet,but you can pre-order and of course you can order from PostGIS in Action from Manning directly
to get the chapter drafts we have posted, updates as we polish them, and the final book when it comes out in hard print.
The Amazon listing would have been so much more exciting, had they not stripped me of my last name or had Leo married to himself.
UPDATE: It appears I now have a last name again
In hind sight, I suppose OBE is more commonly seen as a title of honor rather than a last
name, so its only fitting that I should be stripped of mine and Tim Berners-Lee gets it tacked on at the end of his name.
To find out more about PostGIS WKT Raster, we encourage you to check out these links.
Now we'll itemize 10 things you can do now with PostGIS WKT Raster. In order to use PostGIS WKT Raster, you need PostGIS 1.3.5 or above. Preferably 1.4 or 1.5 or 2.0 alpha.
PostGIS WKT Raster is currently packaged as a separate library and we have windows binaries available.
10 things you can do now with PostGIS WKT Raster
PostGIS WKT Raster introduces a new PostgreSQL datatype called raster which is a companion to PostGIS geometry and geography with its own set of functions for working with raster data and
interoperating with geometry like objects.
- You can load most any kind of raster in your PostgreSQL database with GDAL and the gdal2wktraster.py packaged loader, including
whole coverages, chopping bigger rasters into smaller rasters, or creating overview tables as part of the load process.
- You can also store raster data outside the db and just reference it from inside. Speed doing processing will be slower, but you can share the files.
- You can export your raster data and portions of it or select bands of it to pretty much any format that GDAL supports. Caveats, some kinds of raster band pixel types just don't port well to some raster formats and the exporter
doesn't currently support irregularly blocked rasters (though you can store such things in your database).
- You can read pixel values easily and you can do pixel sampling for selelct areas to make things go much much faster at loss of some precision, as well as other raster properties like geometric extent, pixel size in geometric coordinate units, raster width/height in pixels .
- You can georeference the rasters as well as setting some other properties. The ST_SetValue function for setting individual pixels is still in the works.
- You can intersect rasters with PostGIS geometries.
- You can polygonize rasters or portions based on pixel values and other attributes. Right now you have to write some sql or plpgsql to do this, but as we speak - Jorge Arevalo and others in the
Raster team are working on a ST_DumpAsPolygons, ST_Polygon, as well as others in that family to streamline this process.
- The new raster type supports 13 different pixel band types as documented ST_BandPixelType which includes pixel band types that store floating
- No real limit on the number of bands you can have per raster to my knowledge.
- You can view regularly blocked rasters in Mapserver by defining a PostGIS WKT Raster layer.
We would like to thank all those who have worked on the PostGIS WKT Raster subproject and who have responded to our endless questions:
General monetary or related support Sponsors not already mentioned
Just finished writing the first draft of the last chapter of PostGIS in Action title First look at PostGIS WKT Raster. We now have in place drafts of all the chapters we planned to write. It was probably the most fun chapter to write of all and was lon
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This post was mentioned on Twitter by planetpostgres: Leo Hsu and Regina Obe: PostGIS Raster its on: 10 things you can do NOW with raster http://bit.ly/dpUkX9
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