How to use the osgEarth::RTTPicker.

osgEarth documentation is a little light. The following code snippets show how to setup a node for picking via the RTTPicker.

The key to this is that each node that you wish to pick must be tagged. The method addPlaceNode() does this.

void addPlaceNode(osg::Group *labelGroup, PlaceNode *placeNode)

{

    // Tagging the placeNode makes it selectable by the RTT Picker

    auto objectId = osgEarth::Registry::objectIndex()->tagNode(placeNode, placeNode);

    placeNode->setUserValue("registryId", objectId);

    labelGroup->addChild( placeNode );

}

void placemarkers(osg::Group *labelGroup, osg::ref_ptr<osgEarth::MapNode> mapNode_)

{

    // A lat/long SRS for specifying points.

    const SpatialReference* geoSRS = mapNode_->getMapSRS()->getGeographicSRS();

    // A series of place nodes (an icon with a text label)

    Style pm;

    pm.getOrCreate<IconSymbol>()->url()->setLiteral( "../data/placemark32.png" );

    pm.getOrCreate<IconSymbol>()->declutter() = true;

    pm.getOrCreate<TextSymbol>()->halo() = Color("#5f5f5f");

    // bunch of pins:

    addPlaceNode(labelGroup, new PlaceNode(mapNode_, GeoPoint(geoSRS, -74.00, 40.71),

                 "New York"      , pm));

    addPlaceNode(labelGroup, new PlaceNode(mapNode_, GeoPoint(geoSRS, -77.04, 38.85),

                 "Washington, DC", pm));

    addPlaceNode(labelGroup, new PlaceNode(mapNode_, GeoPoint(geoSRS,-118.40, 33.93),

                 "Los Angeles"   , pm));

    addPlaceNode(labelGroup, new PlaceNode(mapNode_, GeoPoint(geoSRS, -71.03, 42.37),

                 "Boston"        , pm));

    addPlaceNode(labelGroup, new PlaceNode(mapNode_, GeoPoint(geoSRS,-157.93, 21.35),

                 "Honolulu"      , pm));

    addPlaceNode(labelGroup, new PlaceNode(mapNode_, GeoPoint(geoSRS, 139.75, 35.68),

                 "Tokyo"         , pm));

    addPlaceNode(labelGroup, new PlaceNode(mapNode_, GeoPoint(geoSRS, -90.25, 29.98),

                 "New Orleans"   , pm));

    addPlaceNode(labelGroup, new PlaceNode(mapNode_, GeoPoint(geoSRS, -80.28, 25.82), 

                 "Miami"         , pm));

    addPlaceNode(labelGroup, new PlaceNode(mapNode_, GeoPoint(geoSRS,-117.17, 32.72), 

                 "San Diego"     , pm));

    // test with an LOD:

    osg::LOD* lod = new osg::LOD();

    auto placeNode = new PlaceNode(mapNode_, GeoPoint(geoSRS, 14.68, 50.0), "Prague",

                                   pm);

    auto objectId = osgEarth::Registry::objectIndex()->tagNode(placeNode, placeNode);

    placeNode->setUserValue("registryId", objectId);

    lod->addChild( placeNode, 0.0, 2e6);

    labelGroup->addChild( lod );

    // absolute altitude:

    addPlaceNode(labelGroup, new PlaceNode(mapNode_, GeoPoint(geoSRS, -87.65, 41.90,

                                           1000, ALTMODE_ABSOLUTE), "Chicago", pm));

}

In the main setup the above is called thus:

  // Make a group for labels

  osg::Group* labelGroup = new osg::Group();

  mapNode_->addChild( labelGroup );

  placemarkers(labelGroup, mapNode_);

The picker code is started:

   // start with a picker running
   startPicker();
   // Hightlight features as we pick'em.
   installHighlighter();

The picker code is from the osgearth_pick.cpp example (slightly reworked for my application).

Notes:

• RTTPicker halves the framerate at best.
• You can only pick one item at a time.
• Not really for editing.