Accuracy of GPS

Important: These forums are for discussions between SkyDemon users. They are not routinely monitored by SkyDemon staff so any urgent issues should be sent directly to our Customer Support.

Accuracy of GPS

Author	Message
fdemon	fdemon posted 2/22/2022 12:36:17 PM Topic Details Share Topic
Group: Forum Members Posts: 13, Visits: 59	There is a discussion on Flyer Forums about GPS ILS. I understand you are unwilling to extend guidance below 500 feet but it raises the interesting question of how accurate/reliable GPS now is. The impression you get is we are not allowed to use consumer GPSs for precision navigation because 1) there is no separate system that attempts to detect or warn of errors (like RAIM), and 2) there is no specific failure alerting system. As regards 2), it is highly unlikely you would not notice something was wrong. As regards 1), maybe - for the UK - there is virtually no need for error detection because it is virtually impossible that there is a scenario that could impact so many different sources of data. Particularly any risk would be lower than eg VOR, NDB etc You get the impression that typical consumer devices can now track twenty or more satellites from different constellations. This gives the possibility of a huge number of calculations. I am not very familiar with the types of error that effect GPS but you would imagine with a large of number of calculations, it would be trivial to filter out certain systematic errors (eg single faulty satellite). More than that, with so many calculations, you would think just taking an average would be entirely satisfactory. So for a typical tablet, does SD simply get a single calculated position from the host device or does it have access to individual calculations, and if so does it do any processing to pick the best fix?
	Reply Like 1
Tim Dawson	Tim Dawson posted 2/23/2022 10:43:01 AM Post Details Share Post
Group: Forum Members Posts: 7.8K, Visits: 8.5K	The former.
	Reply Like 1
177	1 177 posted 2/23/2022 7:13:21 PM Post Details Share Post
1 Group: Forum Members Posts: 72, Visits: 757	+x Tim Dawson - 2/23/2022 10:43:01 AM The former. Why don't you let people choose what will be the best way of using software? I mean, you can leave it for 500 ft by default and make this limitation switchable in options. This kind of 'Skydemon care' isn't necessary. You know, even with the best pre-planned trips on some days the odds could be really stacked against you. You may be low on fuel, in marginal IMC conditions with an ILS temporarily out of service etc. What would you do? Of course, you're not legally allowed to fly a procedure with a handheld GNSS receiver, but my point is that this kind of emergency situations are happening unintentionally due to weather deterioration. I can assure you from my personal experience that modern GPS chips are far better than most panel-mounted navigators! This $30 L1/L5 signals receiver outperforms my IFR-approved Garmin GNS430 by a MILESTONE! So, just make it as an option and everyone will be happy! It could be a lifesaver some day. Edited 2/23/2022 7:46:10 PM by 177
	Reply Like 4