StrongHarm Posted January 13, 2010 Posted January 13, 2010 Hello, In practical application within DCS is it ever necessary to alter the RAIM threshold values, exclude satellites, or set the elevation mask angle to force reliable GPS info? How often, if ever, is this necessary. Thanks, StrongHarm It's a good thing that this is Early Access and we've all volunteered to help test and enhance this work in progress... despite the frustrations inherent in the task with even the simplest of software... otherwise people might not understand that this incredibly complex unfinished module is unfinished. /light-hearted sarcasm
Waldo_II Posted January 13, 2010 Posted January 13, 2010 I'm no ABRIS pro, but I doubt it. I've never encountered any error that I have noticed. And it isn't like you have a satellite dish that you can point around. If there are any moving parts within the ABRIS, it will all be done automatically. Errors in positioning should be small enough that you won't notice the difference. Perhaps if you found a day and time when satellites are on the perimeter of the sky, and you went into the mountains, but if the ABRIS doesn't get any satellite info, I can imagine it would just use input from the INS until it can establish a link. I cannot say for sure.
Frederf Posted January 14, 2010 Posted January 14, 2010 I'm not sure if the ABRIS's accuracy is anything less than 100% in the sim currently. I haven't noted any inconsistencies between what part of the map I'm over and the chartplotter image. I have been in good GLONASS coverage though. The RAIM threshold is designed to notify you of the positional confidence of the GNSS so it's more of a warning feature than a performance enhancing feature. The manual does state that the RAIM Threshold function will drop an unreliable satellite for a more reliable one, but I'm failing to think of a scenario where that would give any improved performance. I'm pretty sure satellite availability (on/off) is something that can be set in the mission editor but I'm not sure about "faulty" states. If, for example, the mission designer decided that all NAVSTAR (USA) satellites were off limits then life gets more interesting. Later on I read that a low-elevation satellite that is being partially terrain masked can give compromised data. To answer your question, the Auto RAIM Threshold values are not that good at 0.3nm landing and 2.0nm route. Being 3.7km off is not OK in my book. Personally I'd like to be notified on 500m RAIM values in route and 50m around the airfield. One might exclude a satellite where it is expected that it will become problematic later perhaps due to terrain and wish to merely operate without it now as opposed to receiving problematic signals later. Terrain mask is done when expecting interfering terrain (ex: flying down a steep canyon). There is also the benefit that the terrain mask condition will be used by the predictive calculator in estimating future GNSS performance. By doing this you can see that perhaps flying through the route through a canyon will have poor GNSS coverage but 15 minutes later the coverage improves. For the most part all of this isn't necessary as the INU doesn't drift and the ABRIS/GNSS is a secondary navigation system.
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