[MEI-L] coordinates

[Roland, Perry (pdr4h)]

Hello, Thomas,

Welcome to the list!  Thanks for your interest in MEI.

As Johannes and Andrew have already said, if you're working with an existing image, then you can define bounding boxes with the origin at the upper left corner.  Elements representing musical semantics can be related to these bounding boxes using the facs attribute.

If on the other hand, you want to specify where a feature is supposed to wind up in rendered version of the encoding, then x and y coordinates should be used.  Because it's impossible to mandate a single coordinate system for all uses/users, the values of x and y are left to the user.  I suppose these values could be contextual, but it probably would be most useful to employ a single, page-based coordinate system.

MEI provides a page.units attribute on scoredef for recording the real-world units of the output coordinate system.  Currently the values allowed are in, cm, and mm, but this could be extended to include px and other values.

MEI also has a page.scale attribute on the scoredef element that can be used to indicate the relationship between "virtual units" and real-world units given in the page.units attribute.  Virtual units are not currently defined as such, but for relative placement MEI uses half the distance between adjacent staff lines as the basic unit of measurement.  (For example, ho=".5" indicates half of the basic unit or one quarter of the distance between two staff lines.)  Practically speaking, I think this is MEI's "virtual unit".  So a value of 1:1 in page.scale where page.units="cm" indicates that half the distance between adjacent staff lines equals one centimeter.  (Not a realistic example, but you get the idea.)

Of course, all of this stems from my understanding, or lack thereof, of what's needed in MEI for handling graphics.  I freely admit to not being an expert in this area.  If you have suggestions for improvement, please contribute them on this list.

Thanks again for your interest in MEI.  I look forward to hearing from you again soon,

--
p.

__________________________
Perry Roland
Music Library
University of Virginia
P. O. Box 400175
Charlottesville, VA 22904
434-982-2702 (w)
pdr4h (at) virginia (dot) edu
________________________________________
From: mei-l-bounces at lists.uni-paderborn.de [mei-l-bounces at lists.uni-paderborn.de] On Behalf Of Andrew Hankinson, Mr [andrew.hankinson at mail.mcgill.ca]
Sent: Wednesday, February 23, 2011 8:37 AM
To: Music Encoding Initiative
Subject: Re: [MEI-L] coordinates

Hi Thomas,

We're currently using MEI to in an optical music recognition application, and relating the graphical musical symbols (from a scanned book) to the semantic "interpretation" of these symbols via the <facsimile> system that Johannes mentions.

Basically, within facsimile you define a number of bounding boxes using <zone>, defined by ulx,uly/lrx,lry coordinates. These all have a unique ID. Then on every musical element, you use the @facs attribute to refer to the unique ID of the corresponding zone.

We recently did a bit of looking, and apparently in similar applications to ours (METS/ALTO), the standard metric unit is tenths of a millimeter. This gives you the ability to work with integers at a very fine level while maintaining resolution independence. This is not similar to MusicXML's "tenth," which is 1/10th the height of inter-line staff space (i.e., a tenth is equal to 1/40th of a five-line staff).

I don't know if this is at all what you are describing, but I hope it helps!
-Andrew


On 2011-02-23, at 7:20 AM, Johannes Kepper wrote:

> Hi Thomas,
>
> MEI has different approaches to graphics. When you plan to describe an existing image, you should use the @facs-attribute and refer to a zone-element in facsimile (sibling of body). I don't think that this is what you're looking for, but it is surely the better established way to deal with graphics in MEI. The other way is what you already mentioned: Using @x / @y. The unit of this is not clearly defined, but it makes a lot of sense to refer to the unit defined in scoredef. In scoredef/@page.units you can decide whether to use cm / mm or inches. Adding pix to that list would require to specify the resolution (which is not possible yet, I think). There are lots of other interesting attributes for you on scoredef when you consider to render your MEI. The origin for your @x / @y coordinates would be the upper left corner of the page (even though the current documentation does not say so, unfortunately…).
>
> I hope this helps you a bit to get things started. Please ask if you have any further questions – I'm happy to hear more about your project!
>
> Best regards,
> Johannes
>
>
> Am 23.02.2011 um 11:18 schrieb TW:
>
>> Dear MEI list members,
>>
>> I'm exploring different approaches to music encoding and am especially
>> interested in the relationship between graphics and semantics as well
>> as graphical flexibility and precision.
>>
>> One basic question about the graphical capabilities of MEI is how the
>> x/y coordinates are meant to work.  What is the "output coordinate
>> system" that the schema talks about?  Is it page based, staff based
>> like in SCORE, staff/measure based like in MusicXML or maybe dependent
>> on context?  Is there a standard unit like MusicXML's "tenth" or is
>> the encoder free to choose units of his liking?
>>
>> Thanks
>> Thomas Weber
>>
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>
>
> ------------------------
> Dr. Johannes Kepper
> Wiss. Mitarbeiter
> DFG-Projekt Edirom
>
> Musikwiss. Seminar Detmold/Paderborn
> Gartenstr. 20
> 32756 Detmold
>
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> Mail: kepper at edirom.de
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