Hello all We started to port the org.apache.sis.referencing.operation.transform package recently. Conceptually, those "math transform" implementations rely extensively on matrix for many kind of operations, including axis flipping, unit conversions, etc. In the implementation details, some classes use more straightforward code for performance reasons, but those details are hidden from the API - conceptually, we have matrix pretty much everywhere.
Matrices are powerful, and it would be difficult to design a robust Apache SIS without them. Inconvenient is that not every developer feel comfortable with them, which may increase the entry barrier in the sis-referencing and (upcoming) sis-coverage modules. In order to help developers to get their hands in, I don't think that it would be a good idea to avoid matrix usage - in my experience, "intuitive" replacements have more limitations and sometime fuzzy behaviour. This leave us documentation. A while ago I wrote a document for an OGC working group about how we could handle "axis swapping". I don't think that the proposal had been adopted, so all the discussion about Web Map Server (WMS) can be ignored. However the mathematical discussion is still valid: http://people.apache.org/~desruisseaux/discussion/AxisFlip.pdf The above is about one specific matrix usage - there is more to said in other aspects. My concern is: can we structure this kind of information in some Apache SIS document? Not just a copy-and-paste of the above, but some well structured document. Maybe something like my "book" attempt, but in English. Would we have a volunteer for such work? This document would not be that much about Apache SIS classes, but rather about the mathematical concepts that we use in SIS, like the mathematical parts in the above document. About where to put such document: I'm not a big fan of wiki... I think wiki is fine for small drafts, but I'm not sure it is suitable for a "book". Furthermore, our documentation is likely to have many matrix and mathematical equations. I would feel more attracted by "HTML + MathML" or "Docbook + MathML", or maybe epub if it allows MathML (but I do not know epub enough). I would like to know what peoples think? Martin
