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RobertAeiouy

Format for coordinates makes no sense to me

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I notice that coordinates of caches are displayed as degrees, minutes, and decimal fractions of a minute.

Why not either straight decimal (i.e. degrees and decimal fractions of a degree) or straight sexagesimal (i.e. degrees, minutes, and seconds) ?

In other words, why not pick either base 10 or base 60, instead of this unsightly amalgam?

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Decimal minutes vs. Decimal degrees:  Because, historically, consumer handheld GPS units are shipped in boxes from the factory with the decimal minutes coordinate format as the default.  It was easier to "go with the flow" rather than educating new users on how to change the default format setting.

 

Decimal minutes vs. DMS (Degrees, Minutes, Seconds):  Because DMS is terrible for geocaching, due to its lack of precision. On my part of the globe, 1 second represents about 100 feet latitude and 76 feet longitude . That means your coordinates could indicate a spot anywhere within a 7,600 square foot area. Obviously, that lack of precision is not acceptable for geocaching.  Decimal minutes is precise to about six feet (or about a 36 square foot area).

Edited by Keystone
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13 hours ago, Keystone said:

Decimal minutes is precise to about six feet (or about a 36 square foot area).

Of course, that depends on how many decimal places you are using.

As for degrees, minutes, and seconds, if that is not precise enough, one could extend it to a third sexagesimal place. In practice, though, I believe one uses decimal fractions of an arcsecond.

In preparation for my first geocaching outing, I created an app (nothing fancy, I used App Inventor) to display my latitude and longitude in degrees, minutes, seconds, and tenths of an arcsecond. I admit, it was a bit of work to get the formatting right. Also, for testing purposes, I created another version of that app, to display latitude and longitude in degrees and decimal fractions of a degree, to five decimal places. And then I go to the Geocaching site and find out that you use degrees, minutes, and decimal fractions of an arcminute (aargh!) and that there is apparently no option to change the formatting (double aargh!).

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14 hours ago, RobertAeiouy said:

I notice that coordinates of caches are displayed as degrees, minutes, and decimal fractions of a minute.

Why not either straight decimal (i.e. degrees and decimal fractions of a degree) or straight sexagesimal (i.e. degrees, minutes, and seconds) ?

In other words, why not pick either base 10 or base 60, instead of this unsightly amalgam?

 

You are right. The coordinate format used in geocache pages is terrible hybrid system. All positions have different radix and meaning.

 

Some time ago there was an option to show coordinates also in a pure desimal format but that feature was used so rarely that someone desided to remove it.

 

Anyway, coordinates are always stored in a binary desimal format which is more precise than the DMM format used on the cache page. When you download caches into your GPS receiver the GPX file contains these precise decimal coordinates.

 

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33 minutes ago, arisoft said:

When you download caches into your GPS receiver

I think that would be more trouble than just multiplying a number by 60.

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I think you might be overstating the value of adding a few decimal points in order to improve accuracy:

 

image.png.2d7948537349130975415dc30984b6e2.png

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1 hour ago, RobertAeiouy said:

As for degrees, minutes, and seconds, if that is not precise enough, one could extend it to a third sexagesimal place. In practice, though, I believe one uses decimal fractions of an arcsecond.

The convention is to use DDD MM SS.S(S), which works just fine.
The reality is that it doesn't matter what coordinate format you use, they'll all convert in the GPS and get you to the right spot. And since you download the cache listing rather than enter it in manually, you can set your GPS to display whatever coordinate format you want. When first creating a geocache, you can actually use any coordinate format. I do wish that the "edit" geocache page would also allow this method to move and update the coordinates prior to publishing.

Personally, I find the UTM system to be the most "accurate", or rather the most intuitive because it simply resolves to a 1m by 1m grid. Yes, it has it's problems given that the larger woldwide grid isn't perfectly square, but that's why it's divided into smaller quadrants which works just as well.

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1 hour ago, RobertAeiouy said:

In preparation for my first geocaching outing, I created an app (nothing fancy, I used App Inventor) to display my latitude and longitude in degrees, minutes, seconds, and tenths of an arcsecond. I admit, it was a bit of work to get the formatting right. Also, for testing purposes, I created another version of that app, to display latitude and longitude in degrees and decimal fractions of a degree, to five decimal places. And then I go to the Geocaching site and find out that you use degrees, minutes, and decimal fractions of an arcminute (aargh!) and that there is apparently no option to change the formatting (double aargh!).

 

Curious why you'd go through all this.  Did you read the basics in  Geocaching 101 ?

The site's app is free, there are a few partnered apps similar, and thousands of people are playing without issue.  

I load caches I'd do to a GPSr, but many today simply load the app and go.   :)

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2 minutes ago, cerberus1 said:

Curious why you'd go through all this.

Some people like to reinvent the wheel? 

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16 minutes ago, Mineral2 said:

Some people like to reinvent the wheel? 

 

For some of us reinventing the wheel is just fun. My first GPS receiver was fixed to DMS.S format. At that time the cache page showed coordinates also in this format, but not any more.

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3 minutes ago, arisoft said:

 

For some of us reinventing the wheel is just fun. My first GPS receiver was fixed to DMS.S format. At that time the cache page showed coordinates also in this format, but not any more.

But I still don't see why it's an issue. It's not as though when you're navigating you're watching your coordinates to see when they match the coordinates of your destination. You're generally just counting down the direct euclidean distance to your destination.

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11 minutes ago, Mineral2 said:

But I still don't see why it's an issue. It's not as though when you're navigating you're watching your coordinates to see when they match the coordinates of your destination. You're generally just counting down the direct euclidean distance to your destination.

 

Earlier this was a real issue when new cache edit page allowed many formats but users didn't know how to enter coordinates in the correct format. The result was quite random. Today the new cache allows only DMM format but still sometimes one tries to use it as DM.S and again, the cache is not where it should be.

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49 minutes ago, arisoft said:

 

Earlier this was a real issue when new cache edit page allowed many formats but users didn't know how to enter coordinates in the correct format. The result was quite random. Today the new cache allows only DMM format but still sometimes one tries to use it as DM.S and again, the cache is not where it should be.

No, new caches (for the initial coordinate that you enter on the first page) give you a flexible coordinate entry option. This drops down on the "learn about coordinate formats" link:

 

Quote

Coordinate Formats

Coordinates can be entered in any of the formats below (degree, minute and second symbols are optional):

  • N 39 03.857 W 145 12.263
  • N 26 42.773 E 174 32.406
  • N 39° 03' 51.420" W 145° 12' 15.780"
  • 39.064280, -145.204380
  • S 48.8690° E 003.8225°


So you can use DD MM.MMM, DD MM SS.SSS, or DD.DDDDDD. I often use the latter (especially for events) because that's what Google Maps reports back, though I'll take the DD MM.MMM format from my GPS or Basecamp for physical hides.

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I tried to edit the coordinate. It states that DMM must be used. Corrected coordinates allows also many formats.

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Yeah, that's what I was referring to in my first comment. Editing coordinates after creating the listing, but before submitting for publication. That needs to be fixed to allow multiple coordinate formats.

Edited by Mineral2

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On 11/3/2018 at 3:35 PM, cerberus1 said:

Curious why you'd go through all this.  Did you read the basics in  Geocaching 101 ?

 

From Geocaching 101 (emphasis mine):

Quote

Geocaching is a real-world, outdoor treasure hunting game using GPS-enabled devices. Participants navigate to a specific set of GPS coordinates and then attempt to find the geocache (container) hidden at that location.

 

On 11/3/2018 at 4:04 PM, Mineral2 said:

But I still don't see why it's an issue. It's not as though when you're navigating you're watching your coordinates to see when they match the coordinates of your destination.

The last GPS device I owned was a grey box which showed a pair of Roman numerals. You could walk around with it and watch the Roman numerals change. If you wanted to find a place with specific coordinates, you would convert the coordinates to Roman numerals, write those Roman numerals on a scrap of paper, and then carry the box around with you until the Roman numerals on the box matched the Roman numerals on the paper.

 

Old habits die hard.

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3 hours ago, RobertAeiouy said:

The last GPS device I owned was a grey box which showed a pair of Roman numerals.

 

And DDM coords don’t make sense?! 😉

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9 hours ago, IceColdUK said:

 

And DDM coords don’t make sense?! 😉

Those I have to multiply by LX on my abacus.

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On 11/2/2018 at 8:28 PM, RobertAeiouy said:

I notice that coordinates of caches are displayed as degrees, minutes, and decimal fractions of a minute.

Why not either straight decimal (i.e. degrees and decimal fractions of a degree) or straight sexagesimal (i.e. degrees, minutes, and seconds) ?

In other words, why not pick either base 10 or base 60, instead of this unsightly amalgam?

My first order answer is that any of the three possibilities is an arbitrary choice, none with a clear advantage. So it's good enough for me that geocaching.com picked DD MM.mmm for whatever reasons they had.

 

Beyond that, in playing with all three formats for several years now, I find DD MM.mmm more convenient for a few reasons, although all minor. For example, DD.ddddd ends up with a string of decimal places where it's easy to make mistakes like dropping one without noticing, and DD MM SS.s gives me 3 fields to deal with instead of just 2. As a said, minor, really just a matter of taste, but a matter of taste I consider more important than your somewhat arbitrary logical points about straight decimal or straight sexagesimal (well, except SS.s is decimal seconds, so, oops, not any more straight sexagesimal than MM.mmm).

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