Barend Gehrels from the Boost.Geometry project has posted an interesting analysis comparing available versions of the same vector data. It is Shapefile with borders of the World countries. The data is the same but different and sometimes the differences are very surprising.
Here is part 1 and part 2 of the excellent comparison made by Barend.
Regina Obe has just announced that PostGIS in Action book website launched. It is http://postgis.us
I am happy I belong to the hordes of PostGIS users. Recently I asked for a very small addition to the PostGIS manual that will explain the three basic terms of the geospatial geometry: interior, boundary and exterior.
Kevin Neufeld delivered a very well written chapter about Dimensionally Extended 9 Intersection Model (DE-9IM) with series of excellent visualisations of the non-trivial mathematics.
Moreover, Kevin started completing the PostGIS Functions Reference with visual presentation of geometric problems together with SQL commands using various PostGIS functions that can be applied to solve particular situations. For example, what does the ST_Buffer function, how boolean predicates like ST_Contains check spatial relation of two geometries or what’s the difference between ST_Difference and ST_SymDifference.
Clearly, I’ve got way way more than I asked for or I expected. On behalf of myself and users who are about to start their adventure with PostGIS, I’d like to give big kudos to Kevin for this fantastic work!
Together with the recently documented PostgreSQL PostGIS Types and Function Support Matrix, PostGIS team is making abrupt manual a pleasant reading book.
By the way, here is a bunch of references about DE-9IM I found very useful myself:
Quick forward of important announcement to all who care about future of the OpenAerialMap project.
Schuyler Erle called on Facebook:
Join the conf call on restarting OpenAerialMap at the Random Hacks of Kindness code jam!
My countryman Bartosz Milewski – the author of one of the best C++ introductory books – the C++ In Action posted video with very interesting talk about Ownership Systems against Data Races (video is here).
Interestingly, Bartosz proposes to understand the battle with data races as a discipline-driven programming that helps, mostly C+ programmers, to avoid all this horrible pitfalls. Moreover, Bartosz presents programmers with a well-designed methodology based on types system as a tool that may guard programs against injury from data races problem and with success.
Basically (and not surprisingly) Bartosz recommends think first, act later kind of approach based on detailed analysis of what might be causing data races in your program, on identification of potential sources of data race problems. This approach is a contrary to spending hours searching for data races conditions using debugger.
The data race problem is a complex subject, but – in my opinion – Bartosz explains it in a very accessible step-by-step form. Three words summary of Bartosz’ lecture and the presented methodology is: sharing + mutability + no synchronisation = data race
My friend Jo asked on GEOS mailing list for approachable explanation of spatial relations and Dale Lutz from Safe Software suggested something I’ve not came across myself before and what (in generalised form) I’d consider as a great idea for…a book really :-)
It really must be very hot and fresh news, so the virtual devil spirit of social networking hasn’t fished it out yet and also Google (check this if you haven’t heard yet about this local family company) lists less than 15 pages.
PostGIS provides over 300 spatial operators, spatial functions, spatial data types and spatial indexing enhancements. If you add to the mix the complimentary features that PostgreSQL and other PostgreSQL related projects provide, then you’ve got one jam-packed powerhouse at your disposal well suited for hardcore work as well as a valuable training tool for spatial concepts.
Three words: PostGIS In Action. The first book about PostGIS spatial database being written by Regina O. Obe and Leo S. Hsu with release planned for the beginning of 2010. First chapter of the book has been published and is freely available as PDF file through the Manning Early Access Program. Chapter two and three are also available for MAEP subscribers.
Next to the early access, another cool thing about the way Manning Publications release their books is possibility to comment chapters and discuss with authors directly through Manning Sandbox forums. There is no exception for the PostGIS in Action :-)
Update 2009-05-08T23:08:21+00:00: The book official announcement has been posted on postgis-devel and postgresqlonline.com.
I’m looking forward to grab the book!
Pierre, check the TOC for chapter thirteen. Cool, isn’t it?