How to draw a primitive ellipse of kind 'arc'?

[Regina Henschel <regina.henschel@libreoffice.org>]

Hi all,

the element draw:ellipse (10.3.9) has the attribute draw:kind with 
values: full, section, cut and arc. In case of section, cut and arc the 
start angle and the end angle of the arc are given by the attributes 
draw:start-angle and draw:end-angle. It is allowed to determine the 
ellipse by position svg:x and svg:y, and size svg:width and svg:height. 
There are no special attributes for radii and center of the ellipse in 
this case. The attached file has such an ellipse on the first slide.

Problem: How is the curve scaled in respect to the size of the given 
svg:width and svg:height? I see different methods in Apache OpenOffice 
and Calligra Stage.
It looks like both start with an unit circle and calculate a circle arc 
with Startpoint(cos(startangle)|-sin(startangle)) and 
Endpoint(cos(endangle)|-sin(endangle)). But then AOO uses a 
transformation that scales the unit circle to the given svg:width and 
svg:height including the arc as part of the ellipse. And Calligra seems 
to transform the resulted circle arc itself. The attached document has 
screenshots of the resulting rendering.
LibreOffice and PowerPoint render the arc the same way as AOO.

I was not able to say which method is correct using ODF1.2 
specification. It comes down to the definition of svg:width and 
svg:height in (19.571.10 and 19.538.8) with the sentence "For drawing 
shapes that have a non rectangular shape, the length refers to the 
drawing shape's bounding box.". That is not really clear to me. What is 
'shape' in case of the ellipse? Is it the ellipse itself or the arc? And 
what is the meaning of 'the length refers to'?

Kind regards
Regina

Attachment: primitive_ellipse_x_y_width_height.odp
Description: application/vnd.oasis.opendocument.presentation