How Acurate Are Our GPSs

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How Acurate Are Our GPSs

Postby kfxnando » Sat May 28, 2011 6:29 pm

the topic comes up from time to time and have even a discussion with some very clever people, just goes to prove that one can not know every thing about every thing!!

have used certain test over time, self made tests, nothing scientific over a period of time that has led me to come to my own conclusion!!

are they 100% accurate, possibly not 100%!! however very close!!

at some stages drove our vehicles on the limit before we get a fine!!
so if the speed limit was 120km/h drove 129km/h and did not receive any fines and that included driving past the speed traps at such speeds!!

compared to other GPSs in the house, and they are read the same, 3 Garmins and 1 Magellan

have even been told that car speedometers are the accurate one, as they are mechanical devices and thus can not make mistakes when calculating like a GPS
the above was not my statement and did argue against!!

is a GPS the most accurate way of measuring speed?? NO
dont recall the exact name, however the instrument that is used to calibrate GPSs has been used to check to check speeds when records are at stake and concrete proof is needed!!

my latest test, and was not the 1st time that I have done this was a GPS on a commercial flight!!
and then comparing with what the pilots had been doing up front!!

had to hold the GPS by the window all the way to keep signal(suction cup takes a while to settle down and stay on!!), to the displeasure of the one hair hostess!!
the captain was aware of my GPS being on, he had been asked by another air hostess and all was fine!!

on the way to Cape town plane picked up speed as norm, and then slowly lost speed, my thought was that maybe I was holding the GPS in such a way that it was not getting a good signal!!
however the time we took to fly to cape town was consistent with the speed displayed!!
on the way back, the speed was higher and at the one stage it went up and peaked, and my thought maybe the GPS has lost some satellite visibility!!
was holding it by hand and often changed between screens to look at various things!! maps satellite signal levels arrival time . . . . . .!!
the speed climbed and climbed and by now was very convinced the GPS had lost a few things on the way with poor reception and my constant fiddling!!
was very tempted to switch it off and just enjoy the flight and be board!!

however!!
kept the GPS on and we arrived ahead of time!!
so no I was very curious(me)!!
while walking out the cabin was open and asked the flight crew, what speed we were traveling??
what a shocker!!
they quickly explained that in terms of ground speed, they peaked at ''around'' 980km/h
now they had my attention!!
asked why it was slower on the way to CapeTown, they explained that there was often head winds on the way down and obviously back winds on the way up!!

sadly at the peak lost signal and nothing logged!!!! :evil: :evil: :evil:

however do have the end of the one log and the start of the next!!

[quote1 2011/05/27 08:30:39 PM 11529 m 242 m 0:00:01 871 km/h 48° true S30 48.535 E23 09.847
2 2011/05/27 08:30:40 PM 11529 m 15.0 km 0:01:02 870 km/h 47° true S30 48.448 E23 09.960
3 2011/05/27 08:31:42 PM 11529 m 11.6 km 0:00:48 872 km/h 47° true S30 42.981 E23 16.880
4 2011/05/27 08:32:30 PM 11529 m 25.8 km 0:01:46 875 km/h 47° true S30 38.708 E23 22.214
5 2011/05/27 08:34:16 PM 11530 m 10.0 km 0:00:41 881 km/h 47° true S30 29.255 E23 34.061
6 2011/05/27 08:34:57 PM 11533 m 20.4 km 0:01:23 884 km/h 47° true S30 25.568 E23 38.650
7 2011/05/27 08:36:20 PM 11536 m 3.2 km 0:00:13 890 km/h 44° true S30 18.051 E23 47.966
8 2011/05/27 08:36:33 PM 11537 m 4.5 km 0:00:18 890 km/h 44° true S30 16.814 E23 49.369
9 2011/05/27 08:36:51 PM 11538 m 6.0 km 0:00:24 893 km/h 43° true S30 15.084 E23 51.294
10 2011/05/27 08:37:15 PM 11541 m 5.7 km 0:00:23 895 km/h 43° true S30 12.739 E23 53.830
11 2011/05/27 08:37:38 PM 11545 m 9.8 km 0:00:39 901 km/h 44° true S30 10.490 E23 56.269
12 2011/05/27 08:38:17 PM 11548 m 7.0 km 0:00:28 905 km/h 45° true S30 06.725 E24 00.516
13 2011/05/27 08:38:45 PM 11549 m 19.7 km 0:01:18 909 km/h 45° true S30 04.043 E24 03.619
14 2011/05/27 08:40:03 PM 11553 m 8.2 km 0:00:32 918 km/h 45° true S29 56.547 E24 12.328
15 2011/05/27 08:40:35 PM 11558 m 8.7 km 0:00:34 920 km/h 45° true S29 53.455 E24 15.936
16 2011/05/27 08:41:09 PM 11563 m 9.2 km 0:00:36 924 km/h 45° true S29 50.146 E24 19.762
17 2011/05/27 08:41:45 PM 11564 m 10.3 km 0:00:40 927 km/h 45° true S29 46.642 E24 23.841
18 2011/05/27 08:42:25 PM 11565 m 9.5 km 0:00:37 929 km/h 45° true S29 42.735 E24 28.379
19 2011/05/27 08:43:02 PM 11565 m 7.0 km 0:00:27 930 km/h 45° true S29 39.107 E24 32.581
20 2011/05/27 08:43:29 PM 11566 m 8.3 km 0:00:32 932 km/h 45° true S29 36.452 E24 35.645
21 2011/05/27 08:44:01 PM 11568 m 7.3 km 0:00:28 933 km/h 45° true S29 33.293 E24 39.272
22 2011/05/27 08:44:29 PM 11570 m 8.3 km 0:00:32 934 km/h 45° true S29 30.525 E24 42.451
23 2011/05/27 08:45:01 PM 11572 m 10.1 km 0:00:39 935 km/h 45° true S29 27.358 E24 46.082
24 2011/05/27 08:45:40 PM 11574 m 11.4 km 0:00:44 935 km/h 45° true S29 23.498 E24 50.514
25 2011/05/27 08:46:24 PM 11575 m 9.4 km 0:00:36 937 km/h 45° true S29 19.142 E24 55.515
26 2011/05/27 08:47:00 PM 11573 m 11.5 km 0:00:44 938 km/h 45° true S29 15.567 E24 59.602
27 2011/05/27 08:47:44 PM 11575 m 10.7 km 0:00:41 940 km/h 45° true S29 11.189 E25 04.597
28 2011/05/27 08:48:25 PM 11578 m 8.1 km 0:00:31 942 km/h 45° true S29 07.101 E25 09.261
29 2011/05/27 08:48:56 PM 11578 m 7.6 km 0:00:29 944 km/h 45° true S29 03.998 E25 12.786
30 2011/05/27 08:49:25 PM 11575 m 8.7 km 0:00:33 946 km/h 45° true S29 01.083 E25 16.080
31 2011/05/27 08:49:58 PM 11576 m 9.7 km 0:00:37 948 km/h 45° true S28 57.759 E25 19.833
32 2011/05/27 08:50:35 PM 11576 m 8.7 km 0:00:33 950 km/h 45° true S28 54.019 E25 24.043
33 2011/05/27 08:51:08 PM 11579 m 10.1 km 0:00:38 953 km/h 45° true S28 50.674 E25 27.804
34 2011/05/27 08:51:46 PM 11580 m 5.3 km 0:00:20 955 km/h 45° true S28 46.810 E25 32.146
35 2011/05/27 08:52:06 PM 11580 m 2.9 km 0:00:11 956 km/h 46° true S28 44.780 E25 34.442
36 2011/05/27 08:52:17 PM 11582 m 3.7 km 0:00:14 958 km/h 47° true S28 43.684 E25 35.732
37 2011/05/27 08:52:31 PM 11583 m 6.4 km 0:00:24 959 km/h 47° true S28 42.306 E25 37.399
38 2011/05/27 08:52:55 PM 11583 m 4.8 km 0:00:18 961 km/h 46° true S28 39.936 E25 40.253
39 2011/05/27 08:53:13 PM 11586 m 6.1 km 0:00:23 962 km/h 46° true S28 38.137 E25 42.374
40 2011/05/27 08:53:36 PM 11586 m 6.7 km 0:00:25 962 km/h 45° true S28 35.818 E25 45.067
41 2011/05/27 08:54:01 PM 11588 m S28 33.285 E25 47.979
][/quote]

and the next one started

1 2011/05/27 08:55:39 PM 11576 m 271 m 0:00:01 975 km/h 45° true S28 23.284 E25 59.345
2 2011/05/27 08:55:40 PM 11585 m 5.9 km 0:00:22 966 km/h 45° true S28 23.181 E25 59.463
3 2011/05/27 08:56:02 PM 11589 m 12.1 km 0:00:45 965 km/h 45° true S28 20.929 E26 02.015
4 2011/05/27 08:56:47 PM 11590 m 9.4 km 0:00:35 967 km/h 45° true S28 16.291 E26 07.196
5 2011/05/27 08:57:22 PM 11591 m 12.9 km 0:00:48 967 km/h 45° true S28 12.678 E26 11.228
6 2011/05/27 08:58:10 PM 11592 m 7.8 km 0:00:29 968 km/h 45° true S28 07.722 E26 16.759
7 2011/05/27 08:58:39 PM 11593 m 8.6 km 0:00:32 968 km/h 45° true S28 04.741 E26 20.114
8 2011/05/27 08:59:11 PM 11593 m 10.7 km 0:00:40 967 km/h 45° true S28 01.476 E26 23.844
9 2011/05/27 08:59:51 PM 11592 m 11.3 km 0:00:42 965 km/h 45° true S27 57.390 E26 28.490
10 2011/05/27 09:00:33 PM 11597 m 11.5 km 0:00:43 966 km/h 45° true S27 53.104 E26 33.356
11 2011/05/27 09:01:16 PM 11596 m 8.3 km 0:00:31 964 km/h 45° true S27 48.719 E26 38.340
12 2011/05/27 09:01:47 PM 11599 m 8.0 km 0:00:30 964 km/h 45° true S27 45.547 E26 41.905
13 2011/05/27 09:02:17 PM 11600 m 8.3 km 0:00:31 962 km/h 44° true S27 42.468 E26 45.342
14 2011/05/27 09:02:48 PM 11601 m 10.4 km 0:00:39 962 km/h 44° true S27 39.278 E26 48.872
15 2011/05/27 09:03:27 PM 11600 m 7.5 km 0:00:28 962 km/h 45° true S27 35.268 E26 53.313
16 2011/05/27 09:03:55 PM 11603 m 3.7 km 0:00:14 958 km/h 44° true S27 32.392 E26 56.501
17 2011/05/27 09:04:09 PM 11573 m 3.4 km 0:00:13 951 km/h 44° true S27 30.960 E26 58.087
18 2011/05/27 09:04:22 PM 11448 m 4.2 km 0:00:16 944 km/h 43° true S27 29.626 E26 59.534
19 2011/05/27 09:04:38 PM 11244 m 5.5 km 0:00:21 939 km/h 43° true S27 27.978 E27 01.280
20 2011/05/27 09:04:59 PM 10962 m 3.3 km 0:00:13 925 km/h 43° true S27 25.816 E27 03.546
21 2011/05/27 09:05:12 PM 10866 m 3.8 km 0:00:15 912 km/h 43° true S27 24.492 E27 04.921
22 2011/05/27 09:05:27 PM 10794 m 4.6 km 0:00:18 913 km/h 43° true S27 22.982 E27 06.479
23 2011/05/27 09:05:45 PM 10709 m 2.8 km 0:00:11 919 km/h 44° true S27 21.179 E27 08.366
24 2011/05/27 09:05:56 PM 10653 m 4.3 km 0:00:17 918 km/h 45° true S27 20.092 E27 09.550

this goes on till landing, however think post is already long enough!!
if someone would like the rest of the info can post it!!

and as can seen by this time we started descending for landing!!

so our off the shelfs GPSs are not so bad after all!!
sorry for the long post
just though I would share!!
enjoy!! :twisted: :mrgreen:
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kfxnando
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