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

[Byrd, Donald A.]

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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---
Donald Byrd
Woodrow Wilson Indiana Teaching Fellow
Adjunct Associate Professor of Informatics
Visiting Scientist, Research Technologies
Indiana University Bloomington