Table 2.

Horizontal precision estimates of four GPS instruments in three built environment types

Urban Park
					Accuracy Description
GPS ID	N	Satellitesa	HDOPa	PDOPa	CEPa	H95a	H98a
6	1371	10.3	1.00	1.87	1.40	3.30	4.00
14	1398	10.3	1.00	1.83	2.20	4.40	4.90
15	1380	10.4	1.03	1.89	2.30	4.90	6.20
23	1374	10.3	1.06	1.93	2.10	5.00	6.70
Mean ± SDc	1380	10.3 ± 0.0	1.02 ± 0.02	1.88 ± 0.04	2.00 ± 0.35	4.40 ± 0.67	5.45 ± 1.06
Rooftop
6	17284	9.9	1.07	1.89	2.50	5.10	5.90
14	17947	9.4	1.10	1.85	2.20	5.00	5.90
15	17946	9.2	1.09	1.87	2.30	5.20	6.30
23	17944	9.3	1.06	1.82	2.40	5.60	6.60
Mean ± SDc	17780	9.4 ± 0.3	1.08 ± 0.02	1.86 ± 0.03	2.35 ± 0.11	5.23 ± 0.23	6.18 ± 0.29
Urban Canyon – Wall Test
1	762	7.2	1.43	3.53	11.40	48.00	69.10
2	770	7.3	1.40	2.81	20.10	24.60	24.60
6	755	7.7	1.49	2.95	9.50	57.90	78.00
15	774	7.5	1.43	2.96	13.40	34.10	39.10
Mean ± SDb	764	7.3 ± 0.2	1.49 ± 0.04	3.16 ± 0.32	14.04 ± 4.62	43.46 ± 14.73	53.14 ± 25.06

^a HDOP = horizontal dilution of position; PDOP = positional dilution of position; CEP = circular error probable (50%) in metres; H95 and H98 = horizontal accuracy distribution at the 95 and 98 percent levels in metres. All are averaged values.

^b SD = Standard deviation