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

Byrd, Donald A. donbyrd at indiana.edu
Sat Jul 8 20:48:11 CEST 2017 

Before my original suggestion is completely forgotten, I'd like to back up a little. Perry, you said
> 
> I have trouble, as I think most folks would, with values like "2-1/2 half-spaces". I can live with "2-1/2 steps", but still prefer "2-1/2 vu".  We can/should define a "vu" in relation to diatonic steps though.

Gould and Read  rarely if ever saying anything like "2-1/2 half-spaces"; the example I gave, and what they actually say, is "2-1/2 SPACES".  And the fact the "spaces" terminology is used consistently by both in works intended for practical use seems like pretty good evidence that that terminology doesn't bother people much.

Let's see, here's a random note in a random piece of music; I wonder how long its stem is? Ah, it extends all the way across three spaces and halfway across another! :-). It's a standard one-octave stem, with a length of 3 and 1/2 spaces.

--Don


On Jul 7, 2017, at 4:41 PM, "Roland, Perry D. (pdr4h)" <pdr4h at eservices.virginia.edu> wrote:

> Yes, 1 vu = 1 diatonic step.  However, the phrase “diatonic step” doesn’t actually appear in the definition –
>  
> “A single vu is half the distance between the vertical center point of a staff line and that of an adjacent staff line.”
>  
> Even this definition occurs within the description of @vu.height.  This is definitely a place where the Guidelines could use some work.
>  
> --
> p.
>  
>  
> From: mei-l [mailto:mei-l-bounces at lists.uni-paderborn.de] On Behalf Of Craig Sapp
> Sent: Friday, July 07, 2017 2:58 PM
> To: Music Encoding Initiative <mei-l at lists.uni-paderborn.de>
> Subject: Re: [MEI-L] Coordinate system confusion [and terminology]
>  
> > We can/should define a "vu" in relation to diatonic steps though.
>  
> Is that not already the case? Otherwise, I am confused...  In other words 1vu = 1 diatonic step (such as E to F, or G-flat to A-sharp since the chromatic alteration does not matter).
>  
>  
>  
> On 7 July 2017 at 20:45, Roland, Perry D. (pdr4h) <pdr4h at eservices.virginia.edu> wrote:
> 
> I have trouble, as I think most folks would, with values like "2-1/2 half-spaces". I can live with "2-1/2 steps", but still prefer "2-1/2 vu".  We can/should define a "vu" in relation to diatonic steps though.
> 
> --
> p.
> 
> 
> > -----Original Message-----
> > From: mei-l [mailto:mei-l-bounces at lists.uni-paderborn.de] On Behalf Of Byrd, Donald A.
> > Sent: Friday, July 07, 2017 11:23 AM
> > To: Music Encoding Initiative <mei-l at lists.uni-paderborn.de>
> > Subject: Re: [MEI-L] Coordinate system confusion [and terminology]
> >
> > Sure. As I said, both Gould and Ross talk about "half spaces".  --DAB
> >
> > On Jul 7, 2017, at 11:03 AM, "Roland, Perry D. (pdr4h)" <pdr4h at eservices.virginia.edu>
> >  wrote:
> >
> > >
> > > Hi Don,
> > >
> > > You make a good argument for the term "staff-space" or "space".  However, MEI doesn't
> > use this distance as its unit of measurement. Instead, MEI uses *half the distance* between
> > adjacent staff lines, hence the need for a different term.  Perhaps "interline distance" and
> > "virtual unit" aren't intuitive, but they accurately describe the situation, which "staff-space"
> > or "space" do not.  Of course, we could start using the entire distance between staff lines
> > as the unit, but that would mean changing all existing MEI markup and software.
> > >
> > > --
> > > p.
> > >
> > >
> > >> -----Original Message-----
> > >> From: mei-l [mailto:mei-l-bounces at lists.uni-paderborn.de] On Behalf Of Byrd, Donald
> > A.
> > >> Sent: Tuesday, July 04, 2017 11:26 AM
> > >> To: Music Encoding Initiative <mei-l at lists.uni-paderborn.de>
> > >> Subject: Re: [MEI-L] Coordinate system confusion [and terminology]
> > >>
> > >> 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

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