code: function determineGroundResolution(res) {
    
    //iterate over all resolutions
    for (let int = 0; int < res.length; int++) {
      let r = res[int];
  
      //calculate the resolution if not available
      if (!r.groundResolution) {
        r.groundResolution = (0.0254 * r.scale) / r.dpi;
      }
    }
  
  }
docs: Calculates the ground resolution from scale and dpi.
  If `groundResolution` is not set, it will be calculated and set into the array.
  
  @param {Array<Object>} res Resolutions defined with scales like `[ {'dpi': 72, 'scale': 5000 },  {'dpi': 72, 'scale': 10000 } ]`
  @example
  const res = [ {'dpi': 72, 'scale': 5000 },  {'dpi': 72, 'scale': 10000 } ];
  
  determineGroundResolution(res);
  console.log(res);
  // [ { dpi: 72, scale:  5000, groundResolution: 1.7638888888888888 },
  //   { dpi: 72, scale: 10000, groundResolution: 3.5277777777777777 } ]