To get rows in multilevel reports, use the command report/get_result_rows:

svc=report/get_result_rows&params={"tableIndex":<uint>,
				   "indexFrom":<uint>,
				   "indexTo":<uint>}

You can find an example of this request in the sample Reports.

[
	{
		"n":<uint>,	/* row index (from 0) */
		"i1":<uint>,	/* number of first message in specified interval */
		"i2":<uint>,	/* number of last message in specified interval */
		"t1":<uint>,	/* time of first message in specified interval */
		"t2":<uint>,	/* time of last message in specified interval */
		"d":<int>,	/* quantity of rows with next nesting level */
		"c":[		/* cells array */
			<text>,		/* text value of cell */
			{		/* or object */
				"t":<text>,	/* cell value */
				"y":<double>,	/* latitude */
				"x":<double>	/* longitude */
			}			
		]
	}
]