Why osgEarth render map with elevation layer so slowly?

[smarttigerfly]

When I render map with elevation layer using osgearth, it run very slowly, and the result is this:

The main.cpp is:

#include <osgViewer/Viewer>
#include <osgEarth/MapNode>
#include <osgEarth/TMS>
#include <osgEarth/EarthManipulator>
#include <osgEarth/Composite>
#include <osgEarth/GeodeticGraticule>
#include <osgEarth/GLUtils>

using namespace osgEarth;
using namespace osgEarth::Util;

int main(int argc, char** argv)
{
    osg::setNotifyLevel(osg::WARN);
    osgEarth::setNotifyLevel(osg::NotifySeverity::INFO);

    osgEarth::initialize();
    osg::ArgumentParser arguments(&argc, argv);
    // initialize a viewer:
    osgViewer::Viewer viewer(arguments);
    EarthManipulator* manip = new EarthManipulator();
    viewer.setCameraManipulator(manip);

    // create the empty map.
    Map* map = new Map();
    map->setProfile(Profile::create(Profile::GLOBAL_GEODETIC));

    //ImageLayer
    TMSImageLayer* imageLayer = new TMSImageLayer();
    std::string filename("E:\\osgEarthData\\global_TMS\\tms.xml");  
    imageLayer->setURL(filename.c_str());

    //ElevationLayer
    TMSElevationLayer* elev1 = new TMSElevationLayer();
    elev1->setURL("E:\\osgEarthData\\china_TMS\\Elevation\\beijing\\tms.xml");
    elev1->setTileSize(32);
    map->addLayer(elev1);


    map->addLayer(imageLayer);
    map->addLayer(elev1);

    GeodeticGraticule* gr = new GeodeticGraticule();
    map->addLayer(gr);

    // make the map scene graph:
    MapNode* node = new MapNode(map);
    node->open();  
    node->getTerrainOptions().setMinLOD(1);
    node->getTerrainOptions().setHeightFieldSkirtRatio(0.08);
    node->getTerrainOptions().setGPUTessellation(true);
    node->getTerrainOptions().setPriorityScale(3.0);
    node->getTerrainOptions().setConcurrency(8);
    node->getTerrainOptions().setMinNormalMapLOD(10);
    node->getTerrainOptions().setProgressive(true);

    viewer.setSceneData(node);

    // disable the small-feature culling
    viewer.getCamera()->setSmallFeatureCullingPixelSize(-1.0f);
    // set a near/far ratio that is smaller than the default. This allows us to get
   // closer to the ground without near clipping. If you need more, use --logdepth
    viewer.getCamera()->setNearFarRatio(0.0001);
    GLUtils::setGlobalDefaults(viewer.getCamera()->getOrCreateStateSet());
    viewer.setRealizeOperation(new GL3RealizeOperation());

    viewer.realize();
    // zoom to a good startup position
    manip->setViewpoint(Viewpoint(
        "Home",
        116.52, 40.35, 10.88,   // longitude, latitude, altitude
        0, -9, 73100.49), // heading, pitch, range
        5.0);                    // duration

   return viewer.run();
  
}

[smarttigerfly]

When I build the example application in release mode, and it run as expected.
But the display content has background color between different tiles, how to eliminate background color gaps between different tiles?

The gaps may be due to, the near screen display the high LOD tile, the far screen display the low LOD tile, can force the LOD to be the same?

[remoe]

Try to use skirt_ratio. It does not exists in current documentation of osgEarth. Here is an old documentation about it:

https://github.com/gwaldron/osgearth/blob/7d9604ebfc56a16225de5d92b57c4fbc173e2f49/docs/old_rst/source/references/drivers/terrain/mp.rst

[smarttigerfly]

I want to have a try, but can't built the mp terrain driver in osgearth 3.3. The rex driver options has the attribute heightFieldSkirtRatio which can be set by node->getTerrainOptions().setHeightFieldSkirtRatio(0.08);. It's function seems to be the same with skirt_ratio, because there is conf.set( "skirt_ratio", heightFieldSkirtRatio() ); in TerrainOptions.cpp. But the node->getTerrainOptions().setHeightFieldSkirtRatio(0.08); has no effect on result. Set the 'RangeMode' to be osg::LOD::RangeMode::PIXEL_SIZE_ON_SCREEN through node->getTerrainOptions().setRangeMode(osg::LOD::RangeMode::PIXEL_SIZE_ON_SCREEN);, the result will be better, but still have many the background color gaps between different tiles

[jasonbeverage]

How did you build your elevation dataset? You have to take great care to make sure the edges of neighboring tiles share elevation values or you will get the gaps like you are seeing. osgEarth's GDALElevation layer will take care of that for you or look at our commercial ReadyMap server. Using an image based tool like gdal2tiles won't work correctly.

[smarttigerfly]

The elevation dataset is served by local TMS elevation tiles, which may be generated by gdal2tiles. So you may be right. I will have a try to use other elevation dataset.

[smarttigerfly]

Yes, you are right. Thank you very much!
When I use the .tif elevation dataset, the application runs correctly!

And, another question, the GeodeticGraticule's lines can or not to be set AltitudeSymbol::CLAMP_ABSOLUTE, I didn't find the style set function in class GeodeticGraticule.