Advanced track topics

Custom symbolizer parameters

Styling values assigned to tracks are assumed to remain constant. This allows very fast style caching and reuse of style elements between individual tracks. Two exceptions to this rule exists:

• The symbol field "SymbolKeyField" references a track property that may be different between two tracks with the same styling
• Within composite "CustomSymbolizerParams", the value part of a style item may reference the contents of a track field

Example:

<compositeitem name="CustomSymbolizerParams">
    <valueitem name="SomeColor" value="255,0,0,128"/>
    <!-- {<fieldname>} is used to reference value in track data.
         It is only expanded to track data within compositeitem 
         CustomSymbolizerParams due to styleitem caching considerations -->
    <valueitem name="MyParamName" value="{myfield}"/>
</compositeitem>

Resolved property values within CustomSymbolizerParams are passed to custom symbol providers implementing IRasterSymbolProvider as customParameters to GetSymbol

Display priorities

Track sybmols are assigned an initial, fixed display priority between 0.0 and 1.0. If the priority is adjusted for a group of tracks using the same value, their internal ordering will be unchanged. Using the style item "RelDispPri", the display priority can be adjusted.

<stylecategory name="TrackSymbol">
  <!-- ... -->
  <style>
    <statecondition key="Selected" scope="PerItem" state="Active"/>
    <valueitem name="RelDispPri" value="10.0"/>
  </style>
  <!-- ... -->
  <style>
    <fieldcondition field="cargoclass" value="hazardous"/>
    <valueitem name="RelDispPri" value="1.0" action="add"/>
  </style>
  <!-- ... -->
</stylecategory>

Using the above style setup, it is possible to combine display priorities in a very fine-grained manner. Consider track A and B, A has hazardous cargo, B does not. Basic display pri assigned by the system is A:0.2, B:0.6. If both are unselected, resulting disp pri is A:1.2, B:0.6, A on top. If B is selected, A:1.2, B:10.6, B on top. If both selected, A:11.2, B:10.6, A on top.

Note action="add" in the last valueitem. This causes any occurence of RelDispPri to be added to the existing value rather than just replacing it.

Custom track renderers

The system integrator has the option to implement custom track renderers in order to draw specialised graphics not supported by the provided renderers. Implement ITrackRenderer and override "void Render(ITrackDisplayItems items, IViewportLabelsLayer labelsLayer, DrawingContext dc)". The implementation of "void Render(ITrackDisplayItems items, IWriteableBitmapWrapper target)" can be left empty, it is a legacy interface intended for high performance raster data and should be ignored.

After implementing a custom renderer, it must be added to the list of rendrers. The order is significant, rendering is performed in sequence for each tracks, ie all symbols/icons are rendered in the same pass. Renderers are added in application override of "ITrackRendererFactory".

In some cases, renderers can be grouped in order to control rendering sequence. By doing this it is possible to render multiple parts per track rather than per list of tracks:

        public ITrackRenderManager New()
        {
            ITrackRenderManager _trackRenderManager = new TrackRenderManager(_viewportLabelsLayerFactory);
            _trackRenderManager.Renderers.Add(new TrackCellStatisticsRenderer());
            _trackRenderManager.Renderers.Add(new TrackAreaOfUncertaintyRenderer());
            _trackRenderManager.Renderers.Add(new TrackHistoryRenderer());

            _trackRenderManager.Renderers.Add(new TrackRenderGroup(
                new List<ITrackRenderer>{
                    new TrackCourseSpeedVectorRenderer(),
                    new TrackSymbolRenderer()
                }));

            _trackRenderManager.Renderers.Add(new TrackLabelSetupRenderer(_geoUnitsSetting, _trackRenderManager));
            _trackRenderManager.Renderers.Add(new TrackLabelDecorationRenderer());
            _trackRenderManager.Renderers.Add(new TrackLabelRenderer());

            return _trackRenderManager;
        }

In this example, the speed vector and the symbol is rendered per track, potentially causing the speed vector to be drawn on top of some symbols.

When implementing custom rendrers, please use existing rendrers (for instance TrackCourseSpeedVectorRenderer) as template. Note that styling elements can be added freely in track style xml, these can be used as input to custom renderers in order to set styles, determine level of detail etc. These values should be cached in the same way as for existing renderers.