code: function(x,z){
  				var xx = x / this._scale.x + this.width * 0.5,
  					zz = z / this._scale.y + this._depth * 0.5,
  					y = 0,
  					flxx = ~~x,
  					flzz = ~~zz;
  
  				if(xx >= 0 & xx < this.width && zz >= 0 && zz < this._depth){
  
  					var x2 = ~~Math.min(xx + 1, this.width - 1),
  						z2 = ~~Math.min(zz + 1, this._depth - 1);
  
  					var	a = this.getHeightAtCell(flxx, flzz),
  						b = this.getHeightAtCell(x2, flzz),
  						c = this.getHeightAtCell(flxx, z2),
  						d = this.getHeightAtCell(x2, z2);
  
  					y = Interpolation2D.bilinear(xx,zz, flxx, flzz, x2, z2, a, b, c, d);
  				}
  				return y;
  			}
docs: Computes the elevation of the terrain at the given 2D world coordinate
  (based on current terrain scale).
  
  @param {Number} x scaled world coord x
  @param {Number} z scaled world coord z
  @return {Number} interpolated elevation