Help with Coordinates in Avenza

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Help with Coordinates in Avenza

Postby CraigVIC » Sun 02 Feb, 2020 8:46 pm

I've been doing most of my walking off track lately. I've got a bunch of paper maps with points of interest, mainly waterfalls, and by using the contour lines etc I just drop a pin on the Avenza map where it matches and off I go no dramas so far.

Today I was looking for something but I only had the coordinates 38°35'19.4"S 143°44'60.0"E. So, I just found that spot in Avenza, dropped a pin and set off. I didn't check it too thoroughly because it looked right on the face of it. When I got there I obviously wasn't in the right spot. I checked it against the coordinates (the page where i got them has a google map plugin) only to find I was 650m off. 650m is not a trivial distance where I was and I had to chuck it in.

Anyway, clearly I was kidding myself I knew what was going on.
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Screenshot_20200202-090812_Avenza Maps_copy_768x1664.jpg
Avenza, seems normal.
Screenshot_20200202-090823_Maps_copy_768x1664.jpg
Google maps. Same coordinates?
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Re: Help with Coordinates in Avenza

Postby tom_brennan » Mon 03 Feb, 2020 5:58 am

Your spot in Avenza is not the same as the one in your post.

In Avenza, you've used Degrees and Minutes only - but you're using the seconds as decimals, which is wrong.

In Google, you've used Degrees, Minutes, and Seconds - as per the original co-ordinate.

If I plot those two (different) points on a map, they're around 600m apart, which is pretty much what you are getting!
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Re: Help with Coordinates in Avenza

Postby CraigVIC » Mon 03 Feb, 2020 8:27 am

Thanks, how do I go about converting the minutes and seconds to decimals for avenza? Just use an online tool? Or is there a simple calc?
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Re: Help with Coordinates in Avenza

Postby Warin » Mon 03 Feb, 2020 10:08 am

CraigVIC wrote:Thanks, how do I go about converting the minutes and seconds to decimals for avenza? Just use an online tool? Or is there a simple calc?


Simple relation.

60 seconds = 1 minute (time or arc)

60 minutes (or arc) = 1 degree (of arc)
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Re: Help with Coordinates in Avenza

Postby CraigVIC » Mon 03 Feb, 2020 10:29 am

That's obvious of course. There is two methods of representing the seconds if I am following tom_brennan's comment? Ie 19.4" does not equal .194 in the decimal

Is it as simple as 35'30" equals 35.5' ?
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Re: Help with Coordinates in Avenza

Postby Son of a Beach » Mon 03 Feb, 2020 11:32 am

yes :-) Although I reckon decimal degrees are nicer than whole degrees and decimal minutes:

38°35' 19.4" = 38.58872222222222°

The whole degrees/minutes/seconds thing is fine until you require sub-second accuracy and start using decimal seconds, at which point you're then mixing two number formats, which hurts my tiny brain. Just use one format for a single value!

Degrees with decimal minutes is even worse. Again just pick one format - either add the seconds if you need more accuracy (and not more accuracy than seconds provides), or use just decimal degrees.

(Not having a go at you, or Avenza or Google... just whining in general. I work with coordinates all the time in my job, and I can't figure out how anybody thought that using decimals in either minutes or seconds was a good idea.)
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Re: Help with Coordinates in Avenza

Postby CraigVIC » Mon 03 Feb, 2020 12:18 pm

Ok, I'm pretty sure I have it now. Thankyou for all your help everyone.

After all that I have just figured out how to change the coordinates format in Avenza. Probably better to have learnt something from the whole episode though. It was certainly an exercise in humiliation, I walked more than 15 km all up to fall short by 600m. Lucky there's always another day.
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Re: Help with Coordinates in Avenza

Postby CraigVIC » Mon 03 Feb, 2020 12:22 pm

Son of a Beach wrote:The whole degrees/minutes/seconds thing is fine until you require sub-second accuracy and start using decimal seconds, at which point you're then mixing two number formats, which hurts my tiny brain. Just use one format for a single value!


Yes, it's weird for sure but I guess we're stuck with at as long as there's competitive sports...
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Re: Help with Coordinates in Avenza

Postby Son of a Beach » Mon 03 Feb, 2020 1:05 pm

CraigVIC wrote:
Son of a Beach wrote:The whole degrees/minutes/seconds thing is fine until you require sub-second accuracy and start using decimal seconds, at which point you're then mixing two number formats, which hurts my tiny brain. Just use one format for a single value!


Yes, it's weird for sure but I guess we're stuck with at as long as there's competitive sports...


True, I hadn't thought of it like that. Not for sports, but I also use times in programming a lot, and decimal seconds doesn't bother me there when formatting times mixed with minutes, hours, days, years, etc. Maybe because the base unit built into most APIs is seconds and it's optional (depending on the situation) how many larger units you include, whereas with geographic coordinates, the base units is (at least in my head) degrees. Or maybe I'm just odd.
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Re: Help with Coordinates in Avenza

Postby Rai » Mon 03 Feb, 2020 9:35 pm

(Not having a go at you, or Avenza or Google... just whining in general. I work with coordinates all the time in my job, and I can't figure out how anybody thought that using decimals in either minutes or seconds was a good idea.)

Using decimals of minutes on the latitude scale makes sense in marine navigation. Since 1 minute equals one nautical mile, it is easy to work with tenths of mile rather than tenths of degrees (60 miles). Most of the world is covered in water so this may be the reason why decimals of minutes are commonly quoted. Can't see much value in dealing with seconds though.
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Re: Help with Coordinates in Avenza

Postby Son of a Beach » Wed 05 Feb, 2020 10:59 am

Thanks for educating me. This is genuinely interesting to find that there are good reasons for at least some of the conventions that are just an annoyance to me.
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Re: Help with Coordinates in Avenza

Postby slparker » Wed 12 Feb, 2020 8:33 pm

Why not use MGRS? The coordinates work out in metres and finding the Grid Reference from a gps to paper map couldn't be easier.
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