/usr/include/osgEarthSplat/ is in libosgearth-dev 2.9.0+dfsg-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/osgEarthSplat/Coverage
/usr/include/osgEarthSplat/Export
/usr/include/osgEarthSplat/GroundCover
/usr/include/osgEarthSplat/GroundCoverLayer
/usr/include/osgEarthSplat/LandUseTileSource
/usr/include/osgEarthSplat/NoiseTextureFactory
/usr/include/osgEarthSplat/RoadSurfaceLayer
/usr/include/osgEarthSplat/SplatCatalog
/usr/include/osgEarthSplat/SplatCoverageLegend
/usr/include/osgEarthSplat/SplatLayer
/usr/include/osgEarthSplat/SplatOptions
/usr/include/osgEarthSplat/SplatShaders
/usr/include/osgEarthSplat/Surface
/usr/include/osgEarthSplat/Zone