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[Fixed] How is ETA calculated?

 
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JNT



Joined: 10 Jan 2009
Posts: 414
Location: Sweden

PostPosted: Mon Aug 05, 2013 8:43 am    Post subject: [Fixed] How is ETA calculated? Reply with quote

We went sailing in the Baltic for some weeks, where I used Trekbuddy for navigation. As always it worked almost flawless!

One small issue (as it has been in the past) is the ETA value...

I am still puzzled as to how the ETA is calculated. In the wiki it says :"waypoint estimated time of arrival (based on current speed and direction)"

In the screenshot, it shows 1.15 nautical miles to the next waypoint. The speed in that direction (VMG) is 5 knots. That should take about 14 minutes. The current time was 13h15, so ETA should show 13h29... but it shows 14h12.

Generaly, but not always, the ETA seems more accurate in the beginning and gets worse as time goes by and then seems to stabilise on some (wrong) value.



Screenshot_2013-07-24-13-15-19.png
 Description:
Screenshot
 Filesize:  75.19 KB
 Viewed:  8659 Time(s)

Screenshot_2013-07-24-13-15-19.png




Last edited by JNT on Tue Oct 14, 2014 11:15 am; edited 1 time in total
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kruch
Site Admin


Joined: 02 Jul 2006
Posts: 5665

PostPosted: Mon Aug 05, 2013 1:43 pm    Post subject: Reply with quote

Strange... given these values, 13:29 is indeed correct ETA that TB should calculate.

Code:
final long dt = (long) (1000 * (dist / (vmg / 3.6F)));
final long eta;
if (dt >= 0F) {
  eta = timestamp + dt;
} else {
  eta = timestamp + 2 * -dt;
}
ETA_CALENDAR.setTime(eta);
printTime ...


dist = 2129.8 m (1.15 nmi)
vmg = 9.26 km /h (5 knots)
dt = 828000 ms

That is ETA should be really 13:15:19 + 13m48s = 13:29:06 ... Sad
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JNT



Joined: 10 Jan 2009
Posts: 414
Location: Sweden

PostPosted: Mon Aug 05, 2013 3:13 pm    Post subject: Reply with quote

kruch wrote:
Strange... given these values, 13:29 is indeed correct ETA that TB should calculate.


Wonder where it goes wrong then... Confused

Here is another example from the our trip:



Screenshot_2013-07-20-10-26-24.png
 Description:
 Filesize:  86.09 KB
 Viewed:  8636 Time(s)

Screenshot_2013-07-20-10-26-24.png


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kruch
Site Admin


Joined: 02 Jul 2006
Posts: 5665

PostPosted: Tue Aug 06, 2013 11:04 am    Post subject: Reply with quote

Maybe something in the calendar, it is my custom implementation Confused I'll code a test for it.
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oli_v_ier



Joined: 23 Dec 2013
Posts: 1

PostPosted: Sun Jan 05, 2014 7:36 pm    Post subject: Reply with quote

Same bug for me. See picture attached.


DSCN1076_c.JPG
 Description:
Bug ETA
 Filesize:  219.8 KB
 Viewed:  8028 Time(s)

DSCN1076_c.JPG


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JNT



Joined: 10 Jan 2009
Posts: 414
Location: Sweden

PostPosted: Sat Sep 20, 2014 8:50 am    Post subject: Reply with quote

Guess this has not yet made it to the top of the long to-do list...
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kruch
Site Admin


Joined: 02 Jul 2006
Posts: 5665

PostPosted: Mon Sep 22, 2014 9:16 am    Post subject: Reply with quote

Embarassed

In 1.30. 1.29 is almost finished, and this issue will take some time...
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kruch
Site Admin


Joined: 02 Jul 2006
Posts: 5665

PostPosted: Thu Sep 25, 2014 2:30 pm    Post subject: Reply with quote

I've found a scenario with ETA calc error (the error accumulates due to rounding).

Will be fixed in 1.29.
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JNT



Joined: 10 Jan 2009
Posts: 414
Location: Sweden

PostPosted: Mon Sep 29, 2014 6:19 pm    Post subject: Reply with quote

I will test more thoroughly this coming weekend, but it seems to calculate wpt-eta correctly now! Fantastic! Very Happy
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