[MEI-L] Coordinate system confusion [and terminology]

[Byrd, Donald A.]

This reminds me of another source of coordinate system confusion, namely the term for the distance between staff lines. Verovio source code calls it a "double unit", and half that distance a "virtual unit" or "VU" or just "unit"; none of those terms is at all intuitive. Johannes calls it the "interline distance", which is much better, but rather long, and "half interline distance" is way too long (and clumsy). Well, look at Chapter 1 of _Behind Bars_. Her term is "stave-space", or just "space" for short; half that distance, of course, is a "half space". Ross' _Art of Music Engraving and Processing_, the only other book I know of that says much on the subject, just uses the term "space'. So, for example, both might describe a certain stem length as "2-1/2 spaces".

I submit "stave-space" (or "staff-space" on my side of the Puddle) as the full term and "space" for short are both the most standard and the best terms.

--Don


On Jul 4, 2017, at 11:16 AM, Daniel Alles <DanielAlles at stud.uni-frankfurt.de>
 wrote:

> Thank you, Johannes, that really helped and made that clear. So I can continue using the Edirom-coordinates for ulx etc.
> 
> 
> 
> Zitat von Johannes Kepper <kepper at edirom.de>:
> 
>> Dear Daniel,
>> 
>> that's a real confusion, and we need to make it clearer in the guidelines. *Pixel* coordinates are always with the origin in the top left corner. *Music* coordinates, however, are always bottom up. @ulx and so on are always in pixel units, but @vo (vertical offset) is specified in interline distances (half the distance between two staff lines, or, in other words, the vertical distance between a C4 and a D4, or any other two adjacent notes). If you want to specify that a dynamic is written above its default position, it seems more natural that values go up (i.e., @vo="3"). This means that for musical units the origin has to be bottom left. I know it's confusing in the guidelines, and we will address this at some point. If you don't mind, you're invited to prepare something on Git and submit a pull request ;-)
>> 
>> Hope this helps,
>> jo
>> 
>> 
>>> Am 04.07.2017 um 14:48 schrieb Daniel Alles <DanielAlles at stud.uni-frankfurt.de>:
>>> 
>>> Dear all,
>>> 
>>> at the moment, I am a little bit confused about how MEI defines its coordinate system: It is possible to add the attributes @ulx, @uly, @lrx and @lry to for example a surface, as written in part 12 of the Guidelines, which places the origin of the coordinate system in the upper left corner. All the examples in that part show that behavior, ulx/uly is always 0/0. This would correspond to the coordinate systems used in SVG and DOM and (which is what I use for my work) Edirom Editor. On the other hand it is written in part 22.3, that MEI uses a coordinate system in which "the y-axis points from bottom up". That would mean, that ulx/uly could never be 0/0.
>>> 
>>> So now my questions: Is it sufficient to use the coordinates like in the examples, with the origin in the upper left corner? Would that "override" MEIs original coordinate system? If not: Isn't the possibility to encode areas from top-left to bottom-right corners a semantic error in MEI, if the coordinate system is pointing from bottom-left to top-right?
>>> 
>>> Best,
>>> Daniel
>>> 
>>> 
> 
> 
> 
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---
Donald Byrd
Woodrow Wilson Indiana Teaching Fellow
Adjunct Associate Professor of Informatics
Visiting Scientist, Research Technologies
Indiana University Bloomington