[MEI-L] Coordinate system confusion

[Daniel Alles]

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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