added tutorial for ogGetElevationAt
added tutorial for ogGetElevationAt

robhawkes/WebViewer,OpenWebGlobe/WebViewer,Hvitnov/WebViewer,OpenWebGlobe/WebViewer,robhawkes/WebViewer,Hvitnov/WebViewer,OpenWebGlobe/WebViewer,Hvitnov/WebViewer,robhawkes/WebViewer,OpenWebGlobe/WebViewer,Hvitnov/WebViewer,robhawkes/WebViewer