Which coordinate system is used, when svg:viewBox is missing?

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

Hello all,

the element draw:enhanced-geometry (10.6.2, part 1 ODF1.2) has an 
optional attribute svg:viewBox. This attribute establishes a unit-less 
coordinate system. The values in the attribute draw:enhanced-path are 
used in this coordinate system and it is explicitly referred in the 
description of the enhanced geometry equation identifiers.

So what coordinate system is to be used, if the attribute svg:viewBox is 
missing?

For example consider these shapes:

<draw:custom-shape svg:width="4cm" svg:height="2cm" svg:x="1cm" svg:y="1cm">
	<draw:enhanced-geometry draw:type="non-primitive"
	 draw:enhanced-path="M 0 16200 L 21600 0 14400 21600 Z N" />
</draw:custom-shape>

<draw:custom-shape svg:width="4cm" svg:height="2cm" svg:x="1cm" svg:y="1cm">
	<draw:enhanced-geometry draw:type="non-primitive"
	 draw:enhanced-path="M -10000 6200 L 11600 -10000 4400 11600 Z N" />
</draw:custom-shape>

<draw:custom-shape svg:width="4cm" svg:height="2cm" svg:x="1cm" svg:y="1cm">
	<draw:enhanced-geometry draw:type="non-primitive"
	draw:enhanced-path="M 0 1620 L 2160 0 1440 2160 Z N" />
</draw:custom-shape>

I cannot get from the spec how they should be rendered. Do I miss 
something about a user coordinate system in ODF1.2?

This topic was already in the comment 
https://lists.oasis-open.org/archives/opendocument-users/200601/msg00016.html. 
But I think, it was not solved in issue 
https://tools.oasis-open.org/issues/browse/OFFICE-1869.

I know, that AOO uses svg:viewBox="0 0 21600 21600" because that is 
needed for import and export of the predefined custom-shapes of OOXML 
and AOO uses it too for draw:type="non-primitive". But Calligra Stage 
renders them different for example.

Kind regards
Regina