code: function () {
              ElevationModel.call(this);
  
              this.addCoverage(new GebcoElevationCoverage());
              this.addCoverage(new AsterV2ElevationCoverage());
              this.addCoverage(new UsgsNedElevationCoverage());
              this.addCoverage(new UsgsNedHiElevationCoverage());
          }
docs: Constructs an EarthElevationModel consisting of three elevation coverages GEBCO, Aster V2, and USGS NED.
  @alias EarthElevationModel
  @constructor