TMG angle offset

Started by Holton181, August 20, 2017, 07:49:25 PM

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Holton181

August 20, 2017, 07:49:25 PM Last Edit: January 01, 1970, 01:00:00 AM by Guest
Hi,



I noticed that the TMG line always has an angle offset. To me it appears like this offset is the TC + declination, but it's only my guess.



I have taken a screen dump of OM with heading and TC on the dashboard (don't bother about the compass values), a pic of that road section and a screen dump from another application (FlyIsFun, other road section) with a correct TMG for comparison it's not my device causing the offset somehow.



BR

/Hhttps://uploads.tapatalk-cdn.com/20170820/d4e8fad2b0a643ec28234af5aeb85272.jpg">https://uploads.tapatalk-cdn.com/20170820/f1f0cdf176522c24fa19256a9ea76e05.jpg">https://uploads.tapatalk-cdn.com/20170820/4d4e49a7a05c68b62460d72e2b632fd8.jpg">

orux

#1
August 21, 2017, 07:51:39 PM Last Edit: January 01, 1970, 01:00:00 AM by Guest
Quote from: "Holton181"Hi,



I noticed that the TMG line always has an angle offset. To me it appears like this offset is the TC + declination, but it's only my guess.



I have taken a screen dump of OM with heading and TC on the dashboard (don't bother about the compass values), a pic of that road section and a screen dump from another application (FlyIsFun, other road section) with a correct TMG for comparison it's not my device causing the offset somehow.



BR




Hello!



I think it is a problem with the map. Could you share it, or the map projection/datum?



Have you tested the app with an online map?





orux

Holton181

#2
August 21, 2017, 08:05:33 PM Last Edit: January 01, 1970, 01:00:00 AM by Guest
Here is the maps:

http://www.bengt.nolang.se/kartor/">http://www.bengt.nolang.se/kartor/

Based on official and free Swedish map information from the Lantmäteriet, the Swedish mapping agency. Its not I who put them together tough.



The particular map I was using at this time was the "Topografiska kartan", but I have experienced this issue with several different maps, most likely with online maps too. But I will try it with an online map again next time I'm on the road again.

But I actually have had this issue for a long time, but remembered to take the screen dumps yesterday when my wife was driving and we passed some long, straight road sections.

orux

#3
August 21, 2017, 10:23:12 PM Last Edit: January 01, 1970, 01:00:00 AM by Guest
Quote from: "Holton181"Here is the maps:

http://www.bengt.nolang.se/kartor/">http://www.bengt.nolang.se/kartor/

Based on official and free Swedish map information from the Lantmäteriet, the Swedish mapping agency. Its not I who put then together tough.



The particular map I was using at this time was the "Topografiska kartan", but I have experienced this issue with several different maps, most likely with online maps too. But I will try it with an online map again next time I'm on the road again.

But I actually have had this issue for a long time, but remembered to take the screen dumps yesterday when my wife was driving and we passed some long, straight road sections.


Thanks;



It should work fine in online mercator maps.



That map is a transverse mercator map. And it is very large. Because of that, lines of constant bearing (rhumb lines) are not parallel.



I have to find a solution for that kind of maps.





orux

Holton181

#4
August 21, 2017, 10:35:33 PM Last Edit: January 01, 1970, 01:00:00 AM by Guest
Okay, I (...will pretend I...) understand.



Actually I do know the difference between mercator and transverse mercator maps, but not so much how it affects the TMG. No need to explain though, I trust you completely on this subject.



Do you have an online mercator map covering northern Sweden to recommend for testing?

(not the best kind of projection for this part of the world)

Holton181

#5
August 24, 2017, 02:04:01 PM Last Edit: January 01, 1970, 01:00:00 AM by Guest
Quote from: "orux"
...

It should work fine in online mercator maps.

...


Indeed it does. Tested with openstreetmap cyclemap, attached screen dump (sitting on a train).

Good to know, hope you can find a fix for other projections though.



BR

/H

https://uploads.tapatalk-cdn.com/20170824/fc81320759670c46a03fb48ad7644bd2.jpg">

orux

#6
August 24, 2017, 05:00:09 PM Last Edit: January 01, 1970, 01:00:00 AM by Guest
Quote from: "Holton181"
Quote from: "orux"
...

It should work fine in online mercator maps.

...


Indeed it does. Tested with openstreetmap cyclemap, attached screen dump (sitting on a train).

Good to know, hope you can find a fix for other projections though.



BR

/H


Hello;



could you try laste beta version?



if you go to maps-->map tweaks-->map mode, and then select 'north up' you should see that the map (the large one) rotates if you move it from East to West.



try then the TMG line.





orux

Holton181

#7
August 24, 2017, 06:23:44 PM Last Edit: January 01, 1970, 01:00:00 AM by Guest
Downloaded, installed, 'north up', the large map and  TMG activated.

But unfortunately I will be on a hiking trip in the mountains untill Saturday 2:nd. I will try it out if a good opportunity comes ahead, but not many long, straight trails to use as a reference I'm afraid.



I get back when I have something to report.



BR

/H

Holton181

#8
September 09, 2017, 12:52:29 PM Last Edit: January 01, 1970, 01:00:00 AM by Guest
So, finally did the tests.



With map mode 'Normal' the TMG seams to be correct in 7.1.3betta1.

But with 'Map North up' both the TMG and map itself start to jump back and forth a few degrees, independent of each-other. Very distracting, no confidence about correctness of TMG and actual map north.



What direction up is used when map mode is 'Normal'?

If you find a robust solution to TMG on transverse mercator maps (and other), how correct will the bearing and distance measurement be (when scrolling the map while GPS tracking on)? Are they even affected by map projection?
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