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Great Circles


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Tim Dawson
Tim Dawson
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Ok, I just wanted to make sure we were on the same page. The cross track error is only an issue if you are steering great circles. SkyDemon helps you plan, and steer, rhumb lines. At present we have no plans to help you plan and steer great circles. Helping the user to form a route comprised of consecutive rhumb lines that follow a larger great circle is something I'm open to however.
Tim Dawson
Tim Dawson
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I took a look around inside our routing engine to remind myself of how we used to allow the switch between rhumb lines and great circles, and it turns out the architecture is all still there. For anyone interested, I have produced a beta build of SkyDemon Plan which treats all legs as great circles instead of rhumb lines. That doesn't mean we will necessarily ship something, but it would be nice to get some feedback on how it works. Since supporting this might be much cheaper than I originally thought, we just need to come up with a way of the user selecting which they would prefer.

www.skydemon.aero/start/beta.aspx

T67M
T67M
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[quote]
Tim Dawson - 8/15/2016 2:10:24 PM
I took a look around inside our routing engine to remind myself of how we used to allow the switch between rhumb lines and great circles, and it turns out the architecture is all still there. For anyone interested, I have produced a beta build of SkyDemon Plan which treats all legs as great circles instead of rhumb lines. That doesn't mean we will necessarily ship something, but it would be nice to get some feedback on how it works.
Thanks Tim - the difference in the ground track on long legs is clearly noticeable, but the confusion of having the reverse leg not being a reciprocal heading is clearly apparent, and obviously the heading given on the PLog is only valid at the point of departure.

I like your idea of keeping the Rhumb Line as the default and using that for the PLog, but also drawing a (thinner) Great Circle line where the mid-point cross track difference is greater than a user configurable distance to guide the creation of additional waypoints in the leg if/when the user understands and wants Great Circle Navigation. I feel that the the default value for the cross-track threshold should be quite large so that existing users aren't confused by the changed behaviour.
Edited 8/16/2016 7:35:51 AM by T67M
Stratajet
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T67M - 8/15/2016 7:07:20 PM
[quote]
Tim Dawson - 8/15/2016 2:10:24 PM
I took a look around inside our routing engine to remind myself of how we used to allow the switch between rhumb lines and great circles, and it turns out the architecture is all still there. For anyone interested, I have produced a beta build of SkyDemon Plan which treats all legs as great circles instead of rhumb lines. That doesn't mean we will necessarily ship something, but it would be nice to get some feedback on how it works.
Thanks Tim - the difference in the ground track on long legs is clearly noticeable, but the confusion of having the reverse leg not being a reciprocal heading is clearly apparent, and obviously the heading given on the PLog is only valid at the point of departure.

I like your idea of keeping the Rhumb Line as the default and using that for the PLog, but also drawing a (thinner) Great Circle line where the mid-point cross track difference is greater than a user configurable distance to guide the creation of additional waypoints in the leg if/when the user understands and wants Great Circle Navigation. I feel that the the default value for the cross-track threshold should be quite large so that existing users aren't confused by the changed behaviour.

I'd like to +1 the Great Circle line with heading as a Rhumb on the PLog. It's really frustrating having the GPS being better at getting me there more direct. It was a particular pain when I was in Greenland a few months ago.

ckurz7000
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Stratajet - 1/18/2017 4:53:03 PM
T67M - 8/15/2016 7:07:20 PM
[quote]
Tim Dawson - 8/15/2016 2:10:24 PM
I took a look around inside our routing engine to remind myself of how we used to allow the switch between rhumb lines and great circles, and it turns out the architecture is all still there. For anyone interested, I have produced a beta build of SkyDemon Plan which treats all legs as great circles instead of rhumb lines. That doesn't mean we will necessarily ship something, but it would be nice to get some feedback on how it works.
Thanks Tim - the difference in the ground track on long legs is clearly noticeable, but the confusion of having the reverse leg not being a reciprocal heading is clearly apparent, and obviously the heading given on the PLog is only valid at the point of departure.

I like your idea of keeping the Rhumb Line as the default and using that for the PLog, but also drawing a (thinner) Great Circle line where the mid-point cross track difference is greater than a user configurable distance to guide the creation of additional waypoints in the leg if/when the user understands and wants Great Circle Navigation. I feel that the the default value for the cross-track threshold should be quite large so that existing users aren't confused by the changed behaviour.

I'd like to +1 the Great Circle line with heading as a Rhumb on the PLog. It's really frustrating having the GPS being better at getting me there more direct. It was a particular pain when I was in Greenland a few months ago.


+1 for optionally showing a faint version of the GC course (if the deviation is significant) because it gives me the option to approximate it using several shorter RL segments.

-- Chris.‌‌

greg
greg
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+1.
‌Imagine you plan a transatlantic flight, this would be most useful!

ckurz7000
ckurz7000
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Dou you really rely on a VFR only tool like SD (with probably no map coverage for a transatlantic route) to perform such a flight??????? And if you really perform such a flight in an aircraft with sufficient range not to require at least 4-5 intermediary stops, I bet that aircraft will have more sophisticated means of navigation. But, hey, people do all sorts of crazy things Wink)

-- Chris.‌‌

Edited 1/29/2017 8:21:40 PM by ckurz7000
Stratajet
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ckurz7000 - 1/29/2017 8:21:40 PM
Dou you really rely on a VFR only tool like SD (with probably no map coverage for a transatlantic route) to perform such a flight??????? And if you really perform such a flight in an aircraft with sufficient range not to require at least 4-5 intermediary stops, I bet that aircraft will have more sophisticated means of navigation. But, hey, people do all sorts of crazy things Wink)

-- Chris.‌‌


I have used SD for two transatlantic VFR crossings and can confirm it works fine! The GC plot would have made it much better though since otherwise you have to use a different tool to work out what the track should look like and kind of make it up as you go! I also just did a trip to Norway where it would have been useful.
rg
rg
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I think the option to work either with GC or RL would be a nice addition to the software.  Particularly for planning and knowing that the lines will be in the same place as when the FPL gets entered into the Garmin. 

Personally I'd like to see 2 options. 
1 - use RL or GC (default to using RL).
2 - display both (default to off)

So if you select RL you have the option to also display the GC line in thinner or feint magenta.‌‌

Tim Dawson
Tim Dawson
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So for every trip you'd like the option to specify whether to use GC or RL?
GO

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