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What is the interest of the reference View of the SDM engine?
The reference view is essentially the main view, while additional views like the overview are considered secondary views. Usually, for the reference view, we specially handle transformer issues (for example: there is special handling when you zoom in or out of the reference view.
Usually this is only important with nonzoomable objects. Remember that the relative sizes of nonzoomable objects depends on the transformer. For example, a nonzoomable object demagnified by a factor 2 may appear 2 times larger than a corresponding zoomable object. The reason for this is because the zoomable object appears demagified while the nonzoomable object is not. In detail:
- Zooming the reference view may trigger a relayout of the links if a link layout is specified and if the links (or their end nodes) are nonzoomable. This is needed because when you have orthogonal links with nonzoomable end nodes, the link shape does not stay orthogonal when you zoom.
- Label layout of nonzoomable objects is done with respect to the transformer of the reference view.
- Swim lanes of IlvSwimLanesRenderer are adjusted to the dimensions of the reference view.
- The IlvMapRenderer zooms to fit the map inside the reference view after loading the map.
- The IlvDecorationRenderer sets the specified background color or background pattern only at the reference view, not at the secondary views.
- The IlvLegendRenderer places the legend according to the zoom in the reference view if the legend is specified as nonzoomable (see LegendZooming parameter).
- The IlvDrillDownRenderer adjusts the zoom-visibility filter (see the DrillDownZoom parameter) to the transformer of the reference view.
That's why a reference view is needed.
In general: if all graphic objects are zoomable, the reference view has little or no effect. If some objects are nonzoomable, then the reference view shows the best drawing, while the secondary views show a drawing where the nonzoomable objects occupy more or less space than formally specified in the parameters. (That is: any spacing parameters are only guaranteed for the reference view, not for the secondary views).