Storage of vertex data

For quite a number of the shape primitives, it is possible to support 3D very simply–we just increase the number of dimensions in each vertex, and that’s it (obviously just for storage; it will still require some work for rendering). From the point of view of storing the list of vertices, it would be nice if we could specify the dimensions being used e.g. XZT, and then allow missing dimensions to be specified as constants as we now do for theZ. This will also mean that will will be possible to use a 2D primitive with theZ set as equivalent to a 3D primitive with the z value specified separately to the (x,y) points. This would provide one means of keeping the representation compact. Additionally, it is undesirable to have a separate element for each vertex, since for complex shapes e.g. meshes, this would waste a lot of space: when scaling up to thousands of vertices, this would waste multi-megabytes of XML markup for no good reason.

XML schema

Shape type and representation are stored as unsigned 16 bit integers, counts as unsigned 32 bit integers, and vertices and vectors as double-precision floating point.

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
    <xsd:simpleType name="shapeDetailElement">
        <xsd:union memberTypes="xsd:unsignedShort xsd:unsignedInt xsd:double" />
    </xsd:simpleType>
    <xsd:simpleType name="shapeDetail">
        <xsd:list itemType="shapeDetailElement"/>
    </xsd:simpleType>
    <xsd:element name="shape">
        <xsd:complexType>
            <xsd:simpleContent>
                <xsd:extension base="shapeDetail">
                </xsd:extension>
            </xsd:simpleContent>
        </xsd:complexType>
    </xsd:element>
</xsd:schema>

Properties

Store at the level of the ROI, not the shape. Since all the shapes within a ROI describe a single entity, there is no need for separate properties (colour, line thickness/style/endings etc.) on each shape.

Note

J-M Burel: previous discussion about that. Need to review the notes taken at the time.