getTileHeight() {
    if (this.isTiled) {
      return this.fileDirectory.TileLength;
    }
    if (typeof this.fileDirectory.RowsPerStrip !== 'undefined') {
      return Math.min(this.fileDirectory.RowsPerStrip, this.getHeight());
    }
    return this.getHeight();
  }
Returns the height of each tile.
@returns {Number} the height of each tile