When to use createWorldToLocal of osgEarth::GeoPoint?

Does createWorldToLocal of osgEarth::GeoPoint use the ECEF coordinate system?

osg::Matrixd mat;
osgEarth::GeoPoint mapPt(pMap->getSRS()->getECEF(),lon,lat,alt,ALTMODE_ABSOLUTE);
mapPt.createWorldToLocal(mat);

Yes.
Throughout osgEarth, the term "world" refers to the actual XYZ coordinate system used for rendering. For a round-earth map, the world coordinate system is ECEF. (For a projected map, world coordinates are the same as map coordinates.)

The createWorldToLocal function creates a matrix that transforms a point from World coordinates into a local tangent plane centered on the GeoPoint.

Hope this helps!

Thank you for your question and answer.