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ckurz7000
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There are a few facts which maybe ought to be all together on one page: - The shortest course between to points on a sphere is a GC route. A RL is a course of constant heading between two points, which will always be longer than the corresponding GC course.
- To follow a GC track, one has to fly a constantly changing heading, beginning to end. This brings up conceptual problems in how to represent the leg on the PLOG, since you don't have one single heading describing it.
- For the vast majority of pilots there will not be a perceptible difference between RL and GC courses. Because the difference between them only becomes apparent on long (> 500-1000 miles) mostly east-westerly legs.
- The bigger problem arises when you plan your flight as a RL (e.g., on SD) and fly it as a GC (e.g., a Garmin GPS) or vice versa. In this case you could potentially infringe on some airspace which looked like you would clear it during planning. This also is only a factor on long, predominantly east-westerly legs.
- Apparently it is not a conceptual problem for SD to incorporate either RL (which it does at present) or GC (which it did to some extent in the past). The only question is how to integrate RL and GC into the user interface in a consistent and intuitive way which doesn't confuse those 99% of GA VFR pilots (and SD customers) who are not concerned with this issue.
There are two solutions which I find acceptable with a slight preference for the second one: - Keep everything as it is and, by default, plan and navigate a RL course (so no perceptible change to 99% of users). However, if at any point the RL course deviates by more than a given amount (i.e. 0.5 nm) from the GC course, or if the RL course is more than a set amount (i.e., 5 nm) longer than the GC course, issue a warning under the "Warnings" tab. Alongside with the warning, offer the user the option to show the GC course (maybe as a faint line) so that the leg can be conveniently split into several RL sections, thereby approximating the GC course.
- Alternatively, you could switch over to GC navigation and plot everything as a GC course. The switch would not be noticed by 99% of SD customers anyway. In the PLOG use the average heading over the course for display and computational purposes. You would not need to issue a warning since navigation would always be by GC. There will be an ever so slight error in the PLOG, but hardly noticable since one has to correct for wind anyway which is only a forecast guess. And navigation is done by "following the line", so steering a changing heading isn't an issue in practice. Furthermore, no need to introduce the issue of GC vs RL to unsuspecting pilots who don't know what to do with this. The interface presented to the pilot would be consistent, correct and intuitive.
Greetings, -- Chris.
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Tim Dawson
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Peter, this thread has made it very apparent that the vast majority of PPL flying is conducted using a PLOG with rhumb lines, i.e. a leg with a constant heading to fly. It has also made it apparent (by its duration) that the vast majority of customers are happy with the way things are.
However, we still make efforts to accommodate your original request in some way.
Please try to see this from the perspective of other pilots.
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peter@luthaus.de
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As I started this thread and saw there is another reply: I see still the original points valid and there needs to be no choice between RL and GC, just use GC and there would be no discussion. The arguments are all given before. The option to select between the two would only be nice for training purposes, in real flying RL is not needed. I still find it a pity that SkyDemon behaves against all other industry standard in this respect.
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Tim Dawson
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It should be a solvable problem. Those who have been around these forums a while know that SkyDemon does support GC routes, and I released a beta once where all routes were GC just to test our code. It's finding the right UI to make the feature available but make no impact for the majority, which as SemperFi correctly says really don't know or care about the difference.
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Sky Painter
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+xThe challenge I see with only showing a GC track (without the corresponding RL) is that it is impossible to create a GC-plog due to the varying heading that must be flown. That's why I favour keeping the RL as the core of both the SkyDemon chart and plog, but to additionally show the GC (in blue - I like that idea) on the chart to allow long RL sectors to be broken into shorter sectors which more closely approximate the shortest path. You make a good and valid point.
Mike _________________________________________ Samsung Galaxy Tab A8 – Android 11.0 & SD 4.0.2.0 Huawei P30 – Android 11.0 & SD 4.0.2.0
PC – Windows 10 (Home Ed) Version 2009, Build 19045.5917, SD 4.0.2.0
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T67M
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The challenge I see with only showing a GC track (without the corresponding RL) is that it is impossible to create a GC-plog due to the varying heading that must be flown. That's why I favour keeping the RL as the core of both the SkyDemon chart and plog, but to additionally show the GC (in blue - I like that idea) on the chart to allow long RL sectors to be broken into shorter sectors which more closely approximate the shortest path.
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Sky Painter
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In the UK, at least, since the majority of routes are likely to be North/South, I think a GC option would be of limited value and I personally, don't see the need for it. However, I can understand only too well, the desire of others to have this option, so, how about:- 1. Show one or the other – user selectable option in Settings, but default should be RL; 2. When selected, show the RL route in magenta, as currently; 3. When selected, show the GC route in blue; I know that displaying a route line in a colour other than magenta it is a radical departure from the norm, but at least there could be no mistaking which is being displayed. Tim – In the case of someone loading a route created by another, would it be possible to check each user's setting and convert the downloaded route if necessary, or would this just be a coding nightmare?
Mike _________________________________________ Samsung Galaxy Tab A8 – Android 11.0 & SD 4.0.2.0 Huawei P30 – Android 11.0 & SD 4.0.2.0
PC – Windows 10 (Home Ed) Version 2009, Build 19045.5917, SD 4.0.2.0
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ckurz7000
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+xI certainly don't think the show-GC option should be on by default, and if having a "bump" on the RL confuses people who have actively chosen to show GC to the point that they're calling your helpdesk then I'm disappointed and the level of PPL navigation being taught. To help get around the helpdesk calls, maybe the GC line could be hidden completely using some simple algorithm, for example if the GC heading at either end of the leg differs by less than 1° from the RL, or if the mid-point cross track difference is less than 0.5nm? Couple that with a description of the line on the "what's here" popup and surely most pilots won't feel the need to call? What's wrong with showing either one or the other? And if you are showing RL in a case where the course separation to GC is larger than, say, 0.5 nm, issue a warning in the "Warnings" tab. -- Chiris.
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T67M
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I certainly don't think the show-GC option should be on by default, and if having a "bump" on the RL confuses people who have actively chosen to show GC to the point that they're calling your helpdesk then I'm disappointed and the level of PPL navigation being taught.
To help get around the helpdesk calls, maybe the GC line could be hidden completely using some simple algorithm, for example if the GC heading at either end of the leg differs by less than 1° from the RL, or if the mid-point cross track difference is less than 0.5nm? Couple that with a description of the line on the "what's here" popup and surely most pilots won't feel the need to call?
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rg
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Fair point. So it’s route level then and leave everything as rl with gc hidden by default
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